[MUSIC PLAYING] Stanford University. OK. Let's get going. Various announcements,
procedural things. A number of people want more
information about grading and what the exams
are like, all of that. I think I mentioned
one-third of the points will come from the midterm,
2/3 from the final. In terms of the
style of the midterm, the midterm is
heavily going to be about making sure you
got down all the factoids from the first
half of the course, that you've got the basics of
each of our proverbial buckets. The second half of
the final is all going to be about
integration, thinking across the different categories. So just a sense of that. Readings. Readings, as they
are coming out, the books are not required until
the second half of the course. The handout on
Monday, I think, said which chapters of
the [? Zebra ?] book you should read. We will shortly get to you which
chapters of the [? Chaos ?] book you should read as well. The readings that
are being posted on the CourseWorks, the
downloads of various published papers, those are required. I'm clear on those
whether this is a paper you should read
all of, if this is one you should read the abstract of. Even if you read all
of, do not read it in some obsessive,
detail-oriented way. The goal is probably to be
able to say, in one or two paragraphs, why this paper
has something pertinent to say about the topic they fell into. You're not sitting there
having to memorize techniques, middle names of the authors,
how many animals, anything like that. In terms of that, it
probably makes sense to read those after the
first lecture of whatever block there is. And hopefully, if
I get organized, I'll be able to get you sort
of a list of the readings further in advance than
one week in advance. Nonetheless, you should
probably hold off reading it until after the lecture occurs. Let's see. What else? People wanted to get a
sense of how long things were going to go. As we'll see today, the
evolution lecture topic will cover two classes. Molecular genetics, which is
what we'll pick up on Monday, I'm guessing one
to one and a half. Behavior genetics following
that, one to one and a half, ethology one. Neurobiology,
endocrinology, we'll have one week devoted
to intro to the topics. And again, that's one where this
is so important for everybody to be up to speed rather
than these being in catch-up sections that week. The whole week, Monday,
Wednesday, Friday, will be devoted to that
with the TAs teaching it. The following week, three more
lectures, more advanced ones. And depending on
proximity to the midterm, there may be a half-lecture
in there on statistics, or maybe not. So this is going to depend
on keeping on schedule. This is a rough approximation. The midterm is going
to be a Monday night. You will be responsible for
material up to the previous Wednesday, and there will
be lots of review stuff. Take a look at the extended
notes being posted. What else? OK. I think that covers most
of the procedural stuff. All of this stuff will
get posted as well. So picking up on the other day. What was happening
the other day? Number one, the trouncing of
Darwin inventing evolution, trouncing of survival
of the fittest, probably most
importantly, trouncing of behavior for the good
of the species, group selection-type arguments. What we saw was, number one, the
rationale for the whole thing. There is a vicious,
un-fightable logic to why hearts have to be the
size they are and kidneys have the filtration
rates they have to have in order to solve the
challenges of leaving as many copies of your genes
in the next generation. And making sense of the
evolution of hearts and kidneys and things like that
could be the worlds of bioengineers and biomechanics
folks with an underlying logic that it's got to
be something that increases the number of copies
of genes that you leave. And the whole rationale for
Wednesday's lecture and today is applying the same sort
of logic to behavior. The whole world of just
as you can optimize sort of the way one's neck, how
long it is if you're a giraffe, you can optimize
behavioral strategies. And again, also for
a caveat, no animal is sitting there, maybe with the
exception of some other apes, sitting there consciously
strategizing along those lines. One saying, so what would
you, as this dandelion, want to do at that point with
this ecological challenge, personifying just to
make things easier. OK. What we then barreled into were
the three major building blocks for thinking about the
evolution of behavior in the framework of contemporary
evolutionary thinking. Number one,
individual selection-- passing on as many
copies of your own genes to the next
generation as possible by way of your own reproducing. The individual
selection-- a chicken is an egg's way to
make another egg. I've now rehearsed that, so
I've got that down right. The whole notion of behavior as
just being this epi-phenomenon in order to do what's needed to
get another copy of the genes into the next generation. Building block number two. Some of the time, the best way
to increase the number of genes you pass on to the
next generation is to help your relatives
do so following that logic of Mendelian relatedness. And people in the
catch-up section, I know, went over issues of, why is it
that you share half your genes with a full sibling, a quarter
with a half sibling, et cetera? So sometimes the way to maximize
is by helping out a relative to do so with,
again, constrained by this vicious
mathematical logic of, it depends on how related
you are to the relative. And thus, you will
gladly lay down your life for one identical twin, two
full siblings, eight cousins. Off you go. So the whole notion
there of insight into why social animals the galaxy
over are so obsessed with kinship and
relatedness, the whole world of who counts as an us,
who counts as a them in terms of
cooperative behaviors playing out along
lines of relatedness. Finally, we saw the third piece,
which was reciprocal altruism. You scratch my back,
I'll scratch yours. Many hands make the task
less scratchy or whatever. And what you see in
those cases, there is a whole world
in which you don't have to be related
to have cooperation. And we saw all the
domains of that bringing in the formalization--
biomechanics person figuring out how strong
a leg bone has to be. A game theorist figuring
out within the realm of social behavior
when you cooperate and when you don't and
what sort of strategies. Game theory, of seeing
the prisoner's dilemma as the building block
of that entire field and seeing all the strategies
worked out by mathematicians and economists and diplomats
and seeing which ones optimize under what circumstance. And then going and
look in the real world and seeing there's all
sorts of animals out there that have evolved optimization
strategies of when to cooperate and when to defect. And what we'll get to as a huge,
huge issue by the time we get to the lectures on aggression,
cooperation, et cetera is, well, that's great when you've
got a cooperative system going. How do they ever start? How do you jump start
cooperation in systems? The evolution of
cooperation, that's something we will get to in
great detail down the line. Finally, what we shifted
to was now saying, great, we've got all these
principles in hand here and our big three building
blocks and all of that. How would it be applied to
making sense of animal behavior out in the real world? And we left with the examples
starting someplace there-- where did it go, yes, that's
it-- of us marching through, know one individual
factoid about some species or other species,
know that there's a big difference between
the genders in size or there isn't, know
that there's not high levels of
aggression in males, know that females
always give birth. Whatever those traits are
as we marched through, using these ideas about
individual selection, kin selection, reciprocal
altruism, you could march through
and logically infer what the social behavior
of this particular species was going to be like,
and you would be right. We saw, for example,
in tournament species, tournament species where you
have high levels of aggression among males, male-male
competition for access to females. As a result, males tend to
be a lot bigger than females. They are being selected
for muscle mass, secondary sexual
characteristics, plumage, big sharp canines for
slashing the other guy. Bringing up this issue of,
in a tournament species, who does the male
want to mate with? What sort of female are males
interested in mating with? The answer being,
anyone who will mate with them because
there's like no cost involved. All that's involved is no
parental behavior, none of that, the cost of sperm. And literally, people
analyze the relative cost of sperm versus eggs
in tournament species. Males are dramatically un-choosy
as to who they mate with. In tournament species, males
have dramatic variability in reproductive
success-- 5% accounting for 95% of the matings. Female choice in a
tournament species. What does a female
want out of a male? She certainly is not going
to get good fatherhood out of the guy. All she wants are good
genes because that's all she could hope
for from the guy. A whole world of
female selectivity for markers of good genes. And as we'll see in the
sexual behavior lectures, a whole world of males
trying to fake out females across the animal
world, suggesting they got better genes than
they actually do. So we will come to that. Then tournament species. Do you see female
abandonment of kids? Absolutely not, because
there's nobody else who's going to take care of them. Coupled with that,
you see single births among those species, low level. High levels of aggression
amongst the males, low levels of parenting. And males tend to live a
lot shorter than females. And what we saw
at the other end, the pair-bonded species was a
completely different picture. Males are being
careful who they're mating with because the
wiring there is you mate, you take care of the kids. High levels of male
parenting, females are thus able to abandon them. Females can have
multiple births. Males are selected to
be as close to females as a male can be. So there's not a big
difference in size. There's not a big difference
in secondary sexual characteristics. There's not high
levels of aggression. There's not big
differences in lifespan. Who does a female
want to mate with? Someone who is going to
be a competent father. Thus the whole world
of pair-bonded species, where males court with
rituals of coming up with food and coming up with
things of that sort. So the most striking thing
about that was, again, going back to the
two skulls I brought in, you could know nothing
more about that species other than this is
an adult female. This is an adult male. And working through
the same logic, you know a huge amount about
the private lives of the species and who's messing around
with who in the bushes. And that's merely by
applying these principles. And likewise saying,
here is a picture of a pair in this
species and you can't tell which one
is who by gender, that tells you a whole
world of predictability at the other end. So a first example of how
much explanatory power you can get out of this. And on the website,
I will find all sorts of appropriate pictures of
tournament and pair-bonding species for you to look at. OK. So a first round of
looking at animal behavior and seeing how once we got
these principles in hand, individual selection, kin
selection, reciprocal altruism, suddenly an awful lot
of stuff makes sense. Next domain where
that's the case. And this is one that has
had a real challenge to the, "Ooh, isn't nature
benign and animals behave for the good of the
species" viewpoint. This one domain probably
proves an individual selection framework more than
anything else out there. OK. Back to our inevitable
National Geographic specials. And somewhere at the end
of whatever the special is, about whatever species,
at some point they usually get some narrator with some
deep, baritone voice coming at that stage and
saying something like, man is the only species
that kills for pleasure. Man is the only-- and look
at how wonderful and benign these rosebushes are. They don't kill. They don't have war. Only humans do. And what occurred, by
about the mid '70s or so, was enough field workers from
a different species reporting, hey, wait a second. We're not the only
species that kills. And we will see
plenty of domains where that makes sense
in the lectures to come. But one particular
version really, really demanded some rethinking
about animal behavior, which was as follows. What is one of the universals,
whether you start with us and go all the way
down to slime molds? It's babies are cute. Everybody likes babies. Babies are adorable. You want to take care of babies. Your eyes dilate as soon
as you're around them. And a longstanding notion that
what infants, what babies, what baby features are about
are, among other things, are means to reduce aggression. And we will see in the ethology
lecture something about that. That was the standard
sound bite forever. And suddenly, you
got field biologists coming back from studying
various species saying, something's up there,
because in my species I see individuals murdering
kids all the time. Whoa, what's up with that? Infanticide within a species. Suddenly, not only are humans
not the only species that kills, we're like
not the only one who goes and kills adorable,
little, Disney infants. Suddenly, all sorts
of species popping up where there was infanticide. And the huge challenge then
became to make sense of this. This first emerged in the
1970s, studies of langur monkeys in India by someone named
Sarah Hrdy reporting this. Soon it was reported among
lions, some other species as well. And the first obvious
response to this was, wait, this can't be because I watch
all the wildlife specials. There's something [? wrong. ?] Oh, there's some sort of
psychopathology going on. This is not a normal population. This is not a normal
population because they live close to humans. There's some disturbance. There's a toxic
waste dump somewhere. They're not a normal
species because you've got the wrong color socks on as
the observer, whatever it is. And this is not normal. This is pathological behavior. But long enough
time goes by, and it becomes clear in all
sorts of species, individuals kill infants. So what is this about? You start to look closely,
and there's patterns. There are patterns to it. The first one
being that it tends to be adult males
who kill infants. The next being,
you look closely, and it's not random
who kills who. It's males killing
infants who are most likely to be the
offspring of, you guessed it, individual selection,
most likely to be the offspring of other males. Competitive strategies for
reducing some other guy's reproductive success. So this began to be seen
in these species that had infanticide. It was male
infanticide of kids who were most likely to be the
offspring of other males. But more patterns popped
up at that time, which is, well, why don't you see
that in any social species where you have competition? And what wound up being
clear after a while is there's only a certain pattern
that you see in species that have competitive infanticide,
which is the average interbirth interval among females is
longer than the average tenure of a high-ranking male. What? Here's what that means. That means you're
some low-ranking guy. You've been working out in
the gym for years on end. You're finally in the position
to boot out the alpha male and take over the whole group. And damn, every single
female in the group has a newborn who they're going
to be nursing for the next two and a half years. So they're not going
to be ovulating, and they're not
going to be ovulating for about three years. And you're likely to be alpha
for only a year and a half or so, where the length of time,
on average, that you are going to be able to be
reproductively active is shorter than
the length of time that females in your
species nurse kids and thus are not ovulating. And suddenly, you have
this brutally clear logic that makes perfect sense from
everything on Monday, which is, go and kill the kids. Go and kill the kids
for two reasons. Number one, by killing the
offspring of some other male, you are decreasing
that individual's reproductive success. This competition is leaving
as many copies of your genes, et cetera. Number two, by killing
an offspring, the female, by stopping nursing,
will soon be ovulating. And thus, you see this
pattern in langur monkeys, vervet monkeys,
patas monkeys, lions, mountain gorillas
and such, where it's always this structure. Competitive infanticide-- a
male takes over a breeding group and goes about systematically
trying to kill the infants. So we've got an enormous
violation there of behavior for the good of the species,
and baby animals are cute and suppress aggression,
all that sort of thing. The clearest demonstration of
that is to look at the fact that one of the species
where this goes on by this vicious sort of
logic of competition, this is one of the species on Earth
that is as close to extinction as you can get--
mountain gorillas. There's maybe 600,
700 of them are left. And these are just
like stunning animals, and they are disappearing
because of habitat degradation, and human presence,
and civil war is sweeping through there,
and all that sort of stuff. But also they are
facing, I think, inevitable extinction
in a decade or two because every now and then,
a male mountain gorilla will systematically go and kill
the infants around in a group by this logic. You can't ask for a much
better demonstration of animals not behaving for the
good of the species or the group-- this
individual selection strategy. So immediately we start
applying some rules to this. Well, when's a circumstance that
a male would come into a group and boot out the previous
reproductive male and take over, and
where he wouldn't be all that fast to try to kill
all the infants in the group? When would a male
take over a group and not be all that thrilled to
do this competitive infanticide strategy? Any guesses? When he's a brother. Yeah. Part two, individual
selection, kin selection. Kin selection, you don't see
the competitive infanticide if the males replacing are
close relatives by exactly that logic. So then you begin to see some
more elegant stuff going on. In some cases, in
a bunch of species, instead of males killing
infants, what happens is the presence of
a new male causes females to miscarry,
pregnant females to miscarry. One version of this, and
this is seen in wild horses, the new male in there
harasses pregnant females to the point of
them miscarrying. Same exact logic again. In a whole bunch
of rodent species, you see something
far more elegant. The new male shows up, and if
you were a pregnant female, the smell of a new male causes
you to miscarry a litter. And the biology
that is completely worked out, going from
the olfactory signaling-- and we're going to hear tons
about olfactory signaling in weeks to come-- going
from the olfactory system to release of a
stress hormone that disrupts uterine
maturation, and you abort. Olfaction-induced abortion. What's up with the
female with that? Why is that a strategy
for her to leave as many copies of her own
genes in the next generation? If this guy is around, she's
got a choice at that point, a choice, again, metaphorically. She has a choice at that point. Either she can go through the
rest of the metabolic costs of pregnancy, give
birth to these kids, and then they get killed. Or at least she can take
the lesser of two evils. [? He ?] spontaneously
aborts at that point. And soon after, she is
ovulating and has a chance again to pass on copies
of her own genes. And this is the whole world
of-- you put a male hamster in with a female
who's just had babies, and he goes and eats the kids. Oh, it's psychopathological. It's not psychopathological. Male hamsters are migratory. If there are kids there, they're
not likely to have been mine. That's the logical thing. Females having been
selected for if there is the smell of a
new male, miscarry. And the same logic again
extending, the smell of a new male, unless
he's a close relative of the previous male. You see the exact same
thing playing out there. Now, all of this, of course,
is very sort of male-biased in terms of this. These are females sort of making
the best of the bad situation. You're some female
langur monkey, and some new male
has come in and is intent on being infanticidal. And you've read
evolutionary biology also. What do you want
to do to maximize copies of your own genes
in the next generation? Well, you've got this kid here
who you're trying to protect. Would you protect that child to
the point of your being killed? Probably not. And you don't see
females doing that. Under what circumstance
would a female be most motivated to defend
her child to the point of her being seriously injured? Older females, older
females who are less likely to have
another child after that. You're on the scene there,
and who else from day one would be most willing
to get injured in order to protect the kid? The maternal grandmother, who
has no reproductive potential at that point. And what you see in
these langur monkeys, the females will defend, not
to the point of serious injury. The older the mother is, the
more strenuously she defends, and the grandmothers
defend even more. Following the same logic
here playing out in that way. But you also have
another option, which is to do something
much more clever. And this is not in
the world after you've given birth, but the world
of when you are pregnant. Because even in
these species that have the competitive
infanticide, the new male was also
perfectly happy to harass a pregnant female. What have females evolved in
a number of primate species? One of the great, all-time
ways of manipulating males. So you're this
pregnant langur monkey, and in comes this new male. And you know you're
going to go through like six more
weeks of pregnancy, and they're going to
be enormously costly, and the damn guy is
going to kill your kids as soon as they're born. And what can you
do and all of that? And you come up with something
very clever physiologically. You go into what is called
pseudo-estrus, estrus being the term for when female
primates are ovulating or sexually receptive,
are in heat. And most primate species
give external signs of when they're ovulating. There is engorgement
of all sorts of tissues around the vagina
and rear end and stuff that humans don't do. But they have some of the
physiological residues, of water retention, for example. So you've got all these external
signs of, I am ovulating, except you're not ovulating
because you're pregnant. You are pseudo-ovulating. You are going through
a pseudo-estrus. You generate the picture of it. So what happens at that
point with this new guy who's just shown up, and here's this
like four-month pregnant female who nonetheless looks like
she's going through estrus? Well, these guys sit there
then and say, well, well, that's kind of nice, and
they go and mate with her. And like two and a half
weeks later, she gives birth. And you know what the
guy's going to do. He's going to sit there and
say, what's the gestation period in my species? [LAUGHTER] [INAUDIBLE], what is it, like
five months or something? I've been here three weeks,
and already she's given birth. Whoa, what a guy. [LAUGHTER] And they fall for it. They fall for it every time. Females, by having these
pseudo-estrus things, the males are not
infanticidal afterward when the female gives birth. So this whole world
that initially makes no sense at
all-- oh, my god, animals killing members of
their own species, even babies, making vicious logic
when applying issues of individual selection
and the qualifications by way of kin selection. Next example, another one
with a similar flavor. And yeah? Wouldn't evolution favor a male
that he didn't figure it out that it was his children? Yep. And I think probably the
most technical, Darwinian way of explaining that is the
well-known propensity of blood flow to either go to
male brains or penises. [LAUGHTER] They just get impulsive
at that point. They don't stop to think and
get the gynecology textbook. That there no doubt
is an advantage for the tiny subset
of male langur monkeys who can actually be like
prudent at that point and think through the logic. It works with males. They fall for it. Suggesting that a lot
of what's going on there is not a conscious,
cognitive strategy. And this is sort of not
a facetious answer, when by the end of next week,
we get to looking at, how do animals
recognize individuals? With a lot of species, there's
not a cognitive strategy. You're not able to sit there
and figure out, wait a second, this isn't making any sense. No. I mean, like not that
logically figure it out, but [INAUDIBLE]
just favor the males that, for any reason,
whether they figure it out, they just feel like
[INAUDIBLE] three weeks instead of five months [INAUDIBLE]. I think what it is
is that there's not a whole lot of males
there who could make sense or who have been selected
for making sense of the fact that mating has something
to do with babies down at the other end of things. I think there's not been
much selection for being able to cognitively do that. Or to have some sort of rule--
if I mate with this individual, any time she
produces a baby, I'm going to be unaggressive
to the baby, unless it's within
this sort of time span. I think that's a little too
much, too fast, [? too ?] evolved in sort of
a primate system. The males fall for it. Another version with a
lot of the same logic. And this became clear-- studies
of baboons, Savannah baboons, in the early '60s,
which is you would have some male,
who male was having a tension with
another adult male. And they're about to have
some sort of clear fight, and one guy is
obviously low ranking, and he's going to get trounced. And here comes the
big, high-ranking male, and this guy is terrified. And what does he do? He looks around frantically
and grabs a baby and holds it to his chest. 1950s National
Geographic special. Why is he doing that? Because infants are comforting,
because babies are cute. And everybody becomes
less aggressive when there's a baby
around, because oh, my god, who would attack somebody
holding an infant? What if the infant's injured? OK. So that's the old version. So applying some
contemporary interpretations, what you wind up seeing, along
comes the threatening male. The subordinate male grabs
an infant and holds it. And what you only begin to
see after a while of studying individuals is, it's not
random which infant he grabs. And you know
exactly what's going to come next, a
very similar theme to the competitive infanticide. When males are doing
"kidnapping" like this, and that is the
term to use, they're not randomly grabbing kids. They're grabbing kids
who are likely to be the offspring of that male. And it is very clear at
that point, mess with me, and your kid's going to get it. And it's clearly
not being played out in any sort of conscious
level like that. But what you see
is, it's not random. And it comes with the
sort of qualifiers that show you even more
how the system is working. So you've got some guy who's
a big, high-ranking male and has obviously fathered all
sorts of kids in the troop. And you're about to
trounce this smaller guy who grabs one of the kids
who's more likely to be his than yours. Logical competitive strategy
of essentially blackmail. You've got a big,
high-ranking male who's dominating everybody
else, except he only joined the troop two weeks ago. In other words, there's
not been enough time for him to have kids yet. When he is threatening
lower-ranking guys, they're less likely
to kidnap against him than kidnap against
the high-ranking male with a long residency. And what you find
even more interesting, which throws you into
this world of, well, are these guys consciously
thinking about this, or do they just smell that
that kid is that guy's kid, and do they just know? In primates, they're
thinking about it. And the way to realize
that is when they screw up and make a mistake. And this one, sort of years ago
I was watching some baboons, and there was this
low-ranking guy. He was actually middle ranking,
and this high-ranking guy was coming at him. And he was a middle-ranking guy
who critically was on his way down. He used to be a
high-ranking guy. He was aging. In other words, he used to
be reproductively active. In other words, there's some of
his kids around in the troop. So he's sitting
there, and here comes this terrifying, high-ranking
male who's coming at him. And our guy gets all agitated,
nervous, looks around, and he grabs a kid, and
it's likely to be his kid. He's grabbed his own kid. Oh, my god, you're
sitting there saying, I'm never going to get a
damn thesis out of this. These animals just ruined
all the theoretical models. He's grabbing the wrong kid. So he's holding the kid there,
and you're sitting there. And you could see the guy's
about five steps away, and he-- so he tosses the
kid in the air-- [LAUGHTER] --just as he's attacked. You will see they act as if
they have made a mistake. They are consciously working
around something like this. So this whole notion of coercive
blackmail and kidnapping, again, it only
makes sense once you begin to see the structures
of individual selection, kin selection, reciprocal altruism. Another example, and this one
makes perfect sense instantly. You look at the world
of female primates in lots of different species,
and there's ranking systems. There is a hierarchy. And what's the
hierarchy built around? You get a rank one below
that of your mother. You inherit your rank. Your mom is the alpha female. You're her first daughter,
so you're number two. And as soon as she
has another daughter, your kid sister is
number three, until you have a first daughter, who
pushes your kid sister down one step. In other words,
dominance hierarchies amongst the females are
entirely nepotistic. Whoa. How can you explain that? Part number two, kin selection. Dominance systems in all
sorts of social species are built around the
nepotism of relatedness. So that makes sense. Next one, next
interesting notion here, which is one of those
choices, one of those choices that are not conscious choices. But you're about
to get pregnant, and you have a choice, as
whatever species you are, do you want to have
a male or a female, or do you want to have a
litter of males or females, or do you want have a
litter that's predominantly male or predominantly female? And it comes down to an issue
now of two things, which is, how much does it cost to
have a female versus a male during pregnancy? And what are the
reproductive probabilities of having a male
versus a female? Back to this issue. You are in a big
tournament species. And as we saw, there's high
degrees of male variability in reproductive success. 5% of the guys are accounting
for 95% of the matings. So you sit there,
and what you've got is a rule that if you go for a
son-- like 90% of sons running around there are never
going to reproduce. And you hit the jackpot and you
have the 5% at the very top, and each of them are
going to like father 30 different kids, going for
males in a tournament species is a big gamble. It's a risky move. Going for a female,
however, there is no female primate
out there who has 420 kids because she
lays eggs like a salmon. Most females there, unless they
have some fertility problem, they all have something
roughly one to five kids or so over the course of the
life of an old-world primate. So female variability
is way down. In other words, what's
a conservative strategy to pass on copies of your genes? Have a daughter. What's a riskier strategy? Have a son. And what that immediately
predicts is two things. Number one, you look in
dominance hierarchies, and the prediction is that
females who are high ranking should show more of a
tendency towards having sons than daughters. And females who are low
ranking, exactly the opposite. And that's what you see in
a bunch of primate species that have this
sort of structure. Next prediction. You should then predict that
when ecological circumstances get tough, when
times are tough, you want to go for the
offspring that costs less. A female fetus is
less calorically demanding than a male fetus. Male fetuses cost more to
bring to term than females do. The prediction should be, during
times of ecological pressure, the percentage of females
being born should increase. And as a measure of
the fact that males are more expensive
as fetuses, something like 53% of
fertilizations in humans are males, about a
53% to 47% ratio. And over the course
of pregnancy, the cost, the increased
metabolic vulnerability of male fetuses, are such that
by the time birth comes around, it's around 51-49. And it's not until
adolescence that it flips over to the typical pattern
of female dominance. You've got to have
more male fetuses to start off with because
they are more expensive, more vulnerable. So this prediction during
times of ecological duress, you should get a bias
towards more females being born, the 50/50 ratio
skewing in that direction. And that's precisely
what you wind up seeing. And you see all sorts
of examples of this. In humans, for example,
during periods of famine, food deprivation, the ratio of
births skew towards females. What you also see as a measure
of that is among humans, a boy, giving birth to a
boy, statistically decreases the body weight, is likely
to decrease the body weight, of the next offspring. It's expensive having
one of those males. And what you wind
up getting, then, is fluctuation as a function
of your dominance rank. If you're high ranking,
it's almost always worth the gamble to go for one
of those high-risk, high-payoff boys. If you're low ranking, go
for the far more conservative female. You've got this fluctuation
around this 50-50 ratio. And this was
something worked out by one of the sort
of founding figures [? just through ?] modern
evolutionary thinking-- a guy named Robert
Trivers in the 1970s, sex ratio fluctuation as a
function of social context. And people have gone and
looked, and it's precisely this. And you get an interesting
bit of conservatism in this, though, which is
there's some circumstance where it makes perfect sense for
you to have a gazillion daughters because that's
the time to do it. And at some point, you're
having a gazillion daughters, and everybody else is having
a gazillion daughters. And suddenly, males become
really valuable because there's not a whole lot of them around. So the logical
thing to do then is to switch over and
start having males. And everything else being
equal, after a while, with a predominance of
males, it's going to make sense to switch over to females. You have density-dependent
selection you will always have oscillating around 50%. Whichever sex is in
the smaller number, that one is immediately
more preferable. Poor ecological conditions
pushes you this way. Dominance rank push you
one way or the other. But in any of those
circumstances, you have an oscillation
around the mean. Whichever is more common
is less desirable. So sex ratio fluctuation. More stuff. Role of kinship, for
example, in vervet monkeys. We talked about
that the other day. Play the sound, an
infant alarm call, and the mother
gets all agitated, and everyone else
looks at the mother. They know that
she is the mother. Sort of demonstration of
awareness of kinship there. Now, another very
interesting social structure to some species, which is we've
seen all of these tournament species. You have one high-ranking male
mating with lots of females and all that sort of stuff
and polygamous systems. What about polyandry--
circumstances where a female is mating
with multiple males? What about circumstances
of stable polyandry, where you get, in effect,
the inverse of a harem? You get a single breeding
female with a number of males? And what is seen with a
very, very high predominance is when polyandry occurs,
you get a type which is called adelphic polyandry. And the second I
tell what it is, it will make perfect,
wonderful sense. OK. Two male lions sharing a pride? That's like not what
you're supposed to see. It's one male lion, and
Mufasa and his, like, brother gets pushed out of there. And like, that's
not what you see when you study Disney lions. There's supposed
to be only one male is the breeder in the pride. And occasionally
you see these prides where instead there
were two males. How can they pull that off? They should be doing competitive
infanticide, all of that. Who were the two males? Yes, you guessed it
somewhere up there before. It'll be two brothers. When you see cases of two
male lions sharing a pride, or flip the other
way, when you see a pride being willing to
tolerate two males in there instead of one, very,
very high likelihood that they are brothers. This technical term--
"adelphic polyandry." And you wind up seeing
one totally wild example of this in humans. As I went over the other
day, looking at our humans, tournament species,
[? the ?] pair bonding. We're somewhere
stuck in between. We're terribly confused. What you see is most cultures
traditionally allow polygamy, but most people are not actually
polygamous, all of that. And somewhere in there, you
got to ask the same question. Hey, is there any polyandry
going on with humans? And there is one wild
cultural example of this. And this is seen in
traditional Tibetan society, and there you get
adelphic polyandry. You have the following
structure in rural areas. A woman will marry a man. And in the process,
she will marry him along with all of his
brothers, all his brothers. She marries the
entire lot of them. It is adelphic polyandry. And you see that. And like it's down
to the point where here's this woman
with her husband and his younger brother
and his younger brother, all the way down to
this infant that she's holding, who's the
youngest brother who's now one of her husbands. And that's what you see. What's the explanation for this? This is a pattern that
you get in agriculturally very impoverished areas
where you got a problem. You've got five
sons or whatever. And with a pattern
of land inheritance where you would otherwise split
up the land amongst the five sons, that's going
to put each of them below subsistence level. What you need to do is
have a way in which they remain as one reproductive unit
so you don't split up the land. You see this adelphic
polyandry, a woman marrying this whole bunch of brothers. And it's in
circumstances where it's trying to keep the small farm
plots from being broken up. But again, the logic
there is the same as you see in lions with two
brothers sharing a pride. What else? Now, somewhere in
there, you begin to get in a realization
that not only do you have males competing with
males for reproductive success and females with
females, but there's intersexual competition. How could this be? How could a planet that
comes up with Valentine's Day have intersexual competition? What is obvious is the
reproductive interests of any given
individual may not be exactly the same
as the individual she or he mates with. What would be an
example of this? Here you have a species in
which males are migratory. It's a tournament species. A male shows up during a mating
season, lots of aggression, lots of secondary
sexual whatever. And he mates with a
female, and she has kids. Hooray. They have parented an offspring,
and they've shared their genes and increased their
reproductive success. Except this being
the species, this guy is going to pack up
and leave the next day. In other words, he
has no investment in the future reproductive
health of that female, whereas she sure does. She would be delighted
for this offspring to thrive and prosper, but
perhaps not at the cost of her future reproduction. What we see here is, between
the male and the female, different reproductive
strategies. And this opens up a
whole bizarre world of intersexual competition. Here's one really bizarre
manifestation of this. OK. Basic Mendelian genetics. Those of you who got
the catch-up this week should have a
vague sense of this by now, Hardy-Weinberg ratios. You've got one parent
has one genotype, just to distinguish the parents
and changes the colors there, all of that. What is it that isn't bothered
with from day one when you learn these sorts of things? It doesn't matter
which one is the male and which is the female,
which is the father and which is the mother. This is just one
of them contributes this profile, one that. What pops out the other side? Basic Mendelian genetics. When making sense
of pedigrees, it doesn't matter which
parent is contributing the homozygotic profile,
the heterozygotic. It doesn't matter which parent. But then, there is a whole
world of genetic traits where, in fact, it does matter
which parent it comes from, because the same
combination of alleles will function differently
whether it came from the mother or from the father. And this was a field that sort
of emerged in the early 1990s, and these are called imprinted
genes, imprinted genes. These are genes where, for
our purposes to define them, these are genes which have
different manifestations, different phenotypic
consequences. These are genes that work
differently depending on which parent they came from. Mendel rolling in his grave. This is not how it's
supposed to work. This obscure world of
imprinted genes violates this. They work differently
depending on which parent you get it from. Dramatic foreshadowing-- when
we get to the ethology lecture, the word "imprinting" is
going to come up again in a totally different sense. This is a purely
molecular term right now. OK. So you get imprinted
genes, imprinted genes. People began to figure
this out in the '90s, that, wait a second, we've got
a completely different profile in these individuals
with a mutation and a particular disease. Here we have these two
very different diseases, and they turn out to have
the exact same mutation in the same gene. What's up with that? If you get that gene from this
parent, you get this disease. If you get it from that
parent, you get that disease. Totally boggling,
making no sense at all. First thing to
have to be solved. What's a mechanism for actually
making a gene work differently depending on which
parent it comes from? For those who care about
these sorts of details, it's a biochemical process
called methylation. You methylate the gene in
one parent's genome and not the other. Don't worry about the details. The main way is there is a
genetic mechanism for making genes work differently depending
on which parent it comes from. So OK, we know how to do it. Why should this happen? Why does this make any sense? And it took a while, and people
began to see patterns to this. And finally this
was put together by an evolutionary
biologist at Harvard named David Haig in
the early '90s, who came up with a unifying
theory which explains it all. And it's very cool. Here's what you see. You begin to look
at imprinted genes. And for our purposes, the
way we can describe them is, this is a gene where if
you get it from one parent, it does what it's
supposed to do. If you get it from another
parent, it's silenced. It never works. It's methylated into silence. These are imprinted genes. So he began to notice something. When you look at
imprinted genes where they are active if they
come from the father, they all tend to be genes
that promote fetal growth. They're all genes that
increase fetal metabolism. They're all genes that
make for a thicker uterus. They're all genes driven
by hormones coming out of the fetus. They're all genes that push
for greater fetal development. And then you look at the
imprinted genes coming from the female, and
they're all genes that tend to slow down
fetal development. What have we got here? We've got that intersexual
competition played out precisely there. You've got this
male hamster who's going to mate and
never be seen again because he's in this category. And what does he want? He could care less what happens
to the future reproductive success of this female. He wants this offspring
of his to survive. The male imprinted genes
push for greater amounts of fetal growth. And the female ones
saying, well, that'll be great if this kid
survives, but I also have a future reproductive
life to think about. Her imprinted genes
tend to counter it. What would this look like? One of the imprinted genes,
first ones identified, which comes [? from ?]
active from the male, codes for a protein called
insulin-like growth factor. Who cares what insulin-like
growth factor does? What's clear from the name
is it's a growth factor. It's one of those things
that make fetuses grow more. It promotes fetal growth. And then meanwhile,
the female hamster has a cognate, an
opposing imprinted gene. What's that one for? That codes the gene for the
insulin-like growth factor receptor. And what her
version does is make for a less responsive receptor. The male was pushing for more of
the insulin-like growth factor. She gets a receptor
that's not as responsive. And you literally have this
co-evolutionary arms race there of male imprinted
genes evolving to push for more and more fetal growth. Female ones pushing for
less and less fetal growth. And you see that coming
out most apparently when you see mutations
in some of these genes. For example, another pair
of imprinted genes, one from the father,
one from the mother, and what you see there
is the father's version promotes invasion, placental
invasion, into the uterus. And that's actually
the term that gynecologists use,
invasion of the fetus into the uterine wall. It promotes more of that. The female version
slows it down. So what if you have
a disease where the male gene relevant to this
is mutated and knocked out of action? You solely have
the female input, which is decreasing fetal
implantation into the uterus. What have you got then? You've got a disease where
fertilized eggs don't implant. On the other side,
suppose there's a mutation in the female
part of this pairing. And as a result, all you
have is the male input driving for more and more
aggressive fetal invasion. What do you have? You wind up with one of
the all time bad cancers you don't want to
get, choriocarcinoma, a cancer of the
uterus, because it's growing completely
out of control being prompted by the fetus. When you take out each of the
voices through a mutation, you see that normally
you're having this tilting, this balancing,
of competition between males pushing for more fetal
growth at the expense of the future reproductive
success of the female, females trying to slow it down. All of the imprinted
genes show this. Amazingly, people now have
even identified imprinted genes that don't work
until after birth, and they work in the brain. And what do they do? The male-derived one does
things like make for infants that suckle more. Ooh, get more
calories out of mom. And the female
version tends to blunt some of the suckling reflexes. It's all built around the
strategy of males and females do not necessarily have
exactly overlapping reproductive strategies. So another version
of it is one-- a male gene which is
pushing towards expression of the fetal enzyme fetal
lactogen, placental lactogen. And what that does is it
makes it easier for the fetus to grab sugar out of the
bloodstream from the mother, and the mother
tries to counter it. And if she's not very
effective at doing it, or if she's rather
over-effective, you get pregnancy hypoglycemia,
pregnancy diabetes. Suddenly, this is mom having
a fight with her offspring over how much calories
they're going to get, the offspring being driven by an
imprinted gene from the father. Totally cool,
totally interesting. There should be a problem
lurking here, though, which is this is a pattern you
only see in tournament species. You got a pair-bonding
species, and there's no reason why a male should be
saying something like, ooh, I want to like ruin her
future reproductive success at the cost of her giving birth. I'm a pair-bonding
vole, and I want her to give birth to a child
the size of an elephant who's going to survive, and
who cares about her future? They're pair bonding. They're in it together
for the rest of time. You don't find imprinted
genes in pair-bonding species. You find imprinted genes
in tournament species. And thus, we get back
to that same issue the other day looking at
tournament versus pair. Where do humans fall into this? And what we've already seen
is, if humans can come up with choriocarcinomas
and things like that, we have imprinted genes. Same punchline again
as the other day-- in terms of the
number of genes we have puts us somewhere
in between tournament and pair-bonding species. Again, we are terribly confused. OK. Let's take a five-minute
break, and we will pick up with more examples. OK. Let's get going again. Two good questions just now. One is, where does homosexuality
fit into all of this? And where it fits in
is about 30 minutes worth of the sexual behavior
lecture sometime in mid-May. It is a challenge for
some of this thinking. The second good question was,
am I capable of speaking louder? I will try. I mumble. OK. Pushing on. So we've just brought in this
whole bizarre, unexpected world of trashing the Hallmark cards
of intersexual competition. Another example of it, a
really interesting one. This was work done
by a guy named William Rice at Santa Cruz
over some years looking at a number of
different fly species. Female flies are polyandrous. They mate with a lot
of different males. And you're a male. You've just mated with a female. And what you would
like more than anything in order to pass on
copies of your own genes is, like, not have some
other guy impregnate her, some other male fly
guy who's intimidating you. Not have some other guy do it. And suddenly, what you see is
this interesting world where, because of the mating
frequency of the females, she will have sperm from a
number of different males inside her at the same time. And suddenly, we get this very
strange world, a whole field of research, of sperm
competition-- sperm competition of
[? regal A teams, ?] and gold medals and
all of that, of sperm competing with the
sperm from other males. And what you see is, in fly
species, the sperm of males make toxins that kill
the sperm of other males. Whoa. That's very elegant. That's very elegant
because it, in part, requires you to come
up with a toxin that isn't toxic to yourself. You can solve that. All sorts of molecular
tricks for doing that. But this makes wonderful sense. You increase the likelihood
of you, the sperm, reaching the goal
line and killing the other guys and all of that. Except there is a
problem for the females, which is these toxins
that the male sperm release aren't such a hot
deal for the female's health. And what Rice did with these
really interesting studies-- I won't go into the details
of it, in large part because I still don't
understand what the guy did. But he was able to
somehow take populations of male and female flies,
and he would hold the females so that they could not evolve
in response to whatever was going on with the
males-- male-male competition for reproduction-- while he
held constant the female-female competition. The females were not evolving. The males were. And what he saw over the
course of 30 generations was this male-male
sperm competition was such that the
male sperm were making such powerful toxins that
they were shortening the life expectancies of the females. Whoa. That's not smart. Whoa. That makes perfect sense. House flies are not
your pair-bonding swans dying in each other's arms
for life sort of organisms. It's a classic case
of the male only has an investment in the
current reproductive bout. And if he can wipe out
the competitor's sperm and, oh, bummer,
the female has now got all sorts of rotty
necrotic lesions in her vagina, this is not a very
reproductively effective female fly down the line. What do I care? I'm off to the next pile
of cow dung after that. You have that same
structure there, but this is a bummer
for the females. The males, left to
their own competition, will evolve more and
more toxic sperm, which exacts more
and more of a price on the future reproductive
success of the females. Now Rice flips things. And now he takes
these populations, and he holds the male
evolution constant and allows the
females to evolve. And over the course
of 30 generations, they have evolved a means
of detoxifying the sperm. So here we have male-male
competition inadvertently being played out in an
intersexual realm as well, where, again, this
co-evolutionary arms race-- totally bizarre. Sperm killing each other, and
sperm damaging the female. And that makes no sense if you
do for the good of the species. Again, very logical in the
context of these models, these models of evolution. OK, final example. And here's one that will become
very relevant way down the line when we're are looking at things
like the biology of aggression. So you've got these
social primates. And in lots of social
mammals, you've got this pattern, which is one
of the genders picks up around puberty and moves
to another group. It's to avoid inbreeding and
everybody having six fingers and tails, if you're a species
that doesn't have a tail, and is perfectly logical. And what you need is just
some sort of [? pattern-- ?] is that the females or the males
of the species which disperse? And no one among the
primates has ever found a good rule for
which primate species have female exogamy or male exogamy,
which gender leaves at puberty. But there's
variability in chimps. It's the females who
leave at puberty. In gorillas, it's the
females who leave at puberty. In baboons, macaques, a few
other Old World monkeys, it's the males who leave at
puberty, with a very critical implication. So you've got baboons. Baboons-- you've got the troop,
and you look at the adult males and adult females in there. The adult females
grew up in that group. The adult males grew
up someplace else and emigrated into
here at puberty. In other words, among the
adult females in this group, they're all relatives. Among the males,
there's no relatives. Meanwhile, next door
with the chimps, it's the females who
have left at puberty. You look at the mature
animals in the group, and it's the males who were
there with all the relatives who have been there
all their life, and the females who
have no relatives. So asking a question. Comparing baboons and chimps,
which of those species has higher levels of male-male
aggression within the group? [INAUDIBLE] Baboons, yeah, because
they're all brothers and brothers-at-arms in
the chimp group there. And none of the adult
males in baboon troops are typically related
to each other. Very high levels of intramale
aggression intragroup. So which species,
on a certain level, has put us to
shame when it comes to the invention of warfare,
of fighting between groups? Chimps, because
you've got bunches of males who cooperate
because they are relatives. And what you wind up
seeing with chimps-- and we will eventually
get to this-- is you see things that are now
termed "border patrols," where a bunch of males from
a group will patrol the edge of their territory. If they encounter a male
from the group over there, they will attack. They will kill him, as
documented by Jane Goodall. Taken to an extreme,
the males of one group will eradicate another group. And if the rule is, I
am killing this guy, we are killing this
guy, not because we don't like the look on
his face, but because he is a member of that group,
this is the United Nations definition of genocide. Chimps have not only come
up with organized warfare between groups,
they have come up with a chimp
version of genocide. What's the driving
force on that? One of the truly scary
things on this planet, which is when all the males
living next door are getting along
with each other. Because when they
do, they suddenly start looking over at this side. Organized males driven by
female exogamy in chimps is where the warfare
pattern comes from. And as you can
guess, when we get to thinking about the biology
of aggression with humans, we are suddenly in this
world of taking non-relatives who were military
recruits and convincing them to pseudo-kinship
themselves into being a band of brothers,
increasing the sense of kinship there. Chimps do this all on their own. So now making sense of
which primate species have high levels of
male-male aggression within group versus between
group, between group are ones where it's the
females who leave at puberty. All these guys
have been together since they were terrorizing
other kids in kindergarten. They're an organized
group against each other. You get intergroup organized
conflict in primates that have female exogamy,
females leaving at puberty. OK. So we've now worked our way
through a bunch of examples here and how to apply
individual selection, kin selection,
that sort of thing. A fourth branch has come into
the field in the last decade or so. And this is one that has had
a lot of controversy, in part because what it is built around
is mistaken by a lot of folks as being an outdated concept. But in part because what
it is actually implying is very controversial
in some realms. And this is this business
of group selection somehow sneaking
back in the back door there and becoming
relevant to the evolution of social behavior. Group selection. You remember Wednesday. All the wildebeests there,
and the elderly wildebeest pushes his way forward and
distributes his bank account and then leaps into the river
and the crocs and all of that. And that makes no sense at all
because animals don't behave for the good of the species. In individual selection,
he got pushed in. Nonetheless, a notion
of group selection has come back into thinking, but
it occurs only under a couple of specialized circumstances. The version that we just
trashed, which was the version Marlin-- OK. How many of you guys know
who Marlin Perkins was? It's come to that. Marlin Perkins. How many of you guys know
what-- does Mutual of Omaha, does that still exist? Mutual of Omaha's Wild Kingdom? Is that still a
television program? Yes, no? When you were young
did that exist? Yeah. OK. Is it still sponsored
by Mutual of Omaha? They still do. That's great, OK,
because that one has been going for decades and decades. And they'd somehow always have
to segue to Mutual of Omaha in there doing the
commercials, building it like, just as rhinos will
mate on for hours on end, you want fire insurance for
your home or some such thing. But in its original
couple of decades, it was hosted by a guy
named Marlin Perkins, and Marlin Perkins
taught most of America their evolutionary biology. Marlin Perkins is the
guy who taught everybody behaving for the good of the
species and that sort of thing. The first version of
group selection that got trashed in the '60s was Marlin
Perkins' group selection. The group selection that's
sneaking back into the field is very different, two
different versions. First one, something you will
get in various populations. You've got a population
of something or others, and some biogeographic
event occurs, which causes a subset
of them to get isolated from everybody else. A land bridge disappears,
or somebody drops a lake there, or who knows what. But something isolates a small
subset of the population. So these guys go about
reproducing by their standards, and these guys go about
reproducing by their standards. And what's going to be
a characteristic very soon of the smaller
population, they're going to be more inbred
than this population simply because they're smaller. They're going to have a
higher degree of relatedness among individuals. So now we throw our second piece
of our three building blocks, throw in kin selection. And what that
immediately predicts is levels of cooperation
will be higher in this group than in this group, because the
higher degree of relatedness. That's great. And that's great
because once we see how these sort of cooperative
systems have a larger payoff, you will get a crystallization
so that everybody, the second or third
cousins, are eventually going to have to be just as
cooperative as the siblings are with each other. You are going to fix
a trait of cooperation in that population
at a high rate. So notice here, in this
case, we have a high degree of cooperation driven
by kin selection, whereas these guys are going
about their usual "savage at each other's
throats" business. Biogeographic event
reverses, and these guys get reincorporated into
the main population. And they're so different
by then that they get a different color. And what you've got then is,
here in the large population, here is a nucleus of
animals who are cooperating, and here is the huge, unwashed
mass of the ones who are not. And everything we know
about reciprocal altruism, all of that, means
that these guys are going to start
out-competing these guys. And the model that is
used is cooperation will have to
crystallize outward. Animals will have to join in
in these cooperative patterns because these guys
will outcompete them. What do we have? This is called a founder effect. This is a small population
that, thanks to being inbred, has fixated some trait
that's advantageous. [? Where ?] the evolution
here moves faster than in here because of the smaller
population with the inbreeding, some adaptive trait
comes in there. They get re-induced into
the main population, and this founder-driven
trait quickly spreads throughout
the population. And what you get here is, if
the same thing is occurring in the realm of behavior,
reciprocal, cooperative behavior, somewhere in
here you have a transition from this being a kin
selection phenomenon to this being a reciprocal
altruism phenomenon. So that stands as one of
the models out there for, how do you jump
start cooperation in non-relative populations? You use inbred founder
populations to drive it there. And just to have a metaphor,
all you need to do, think about in some city
there's some occupations, some mercantile something
or other, that there's a gazillion of them, and all
sorts of people work in that. And there's a subgroup
of people there who work in this
who are all related. And as a result, they
do something cooperative and kin selective. They make low-interest
loans to each other. And as a result, they're
more successful at business, and they get
incorporated into here. And what you then have
is this economic force that everybody
else has to join in to this cooperative business
of trusting each other, or low-interest loans, or
I trust you like a sibling. You don't have to pay
me in full next week. Used to be that only
siblings trusted each other like siblings. But a force there
for more cooperation, a driving force of inbred
kin selection initially. So that's one way
in which people are thinking about group selection. And here you now have
this group out-competing this because of this trait. And people actually use
terms like "crystallization." The trait of cooperation will
crystallize outward and fix in the whole population. So that's one version of it. And this is one, again,
we will come back to, this is one of the ways
to jumpstart cooperation in a world in which there
is no reciprocal altruism. Because you see the
problem with that. We all have learned
tit for tat is the best one, except
[? forgiving ?] tit for tat might be better, except
Pavlov might even be better. And all of those who built
around this one requirement, though, which is somebody
has to make the first move of being cooperative. That's got to
jumpstart the system. And what we all
know is, in a system that doesn't go along with
the rules of can't we all sing "Kumbaya," what
happens is the first one in the first round who does
something cooperative is some schmuck who's one
step behind everybody else for the rest of time. There's no way to get these
cooperative systems to evolve initially. We'll see there are ways. And this is one of those--
have it driven initially by kin selection, and then throw
it into the general population. So that's one version of where
group selection has crept back in. Another version is sort of the
more generalized form of it. And it could be illustrated--
OK, the following example. You've got chickens. You've got chickens
with an array of traits, and you can see there's
two types of chickens. One chicken is super aggressive
and beats on everybody else, and she lays lots of eggs. Another chicken-- far more
pacific and introspective and less aggressive
and has fewer eggs. So now you take any one of
the high-aggression females and one of the low-aggression
guys and put them together, and who's going to leave
more copies of her genes? The high-aggression female
laying lots of eggs. Now instead, you
have a whole group of the high-aggression
females and a whole group of the low-aggression females. What's going to happen in
the high-aggression females? They're all so aggressive that
they all injure each other. They all stress each other
into lower fertility rates, all of that. And suddenly you have
this very important world in which A can dominate
B, but where groups of B dominate groups of A.
And it's in that realm that you suddenly get a push
towards group selection. When selection on that level--
a world of any individual being outcompeted because of a trait. But as a "collective"-- and
bringing in that word not randomly, as a collective
in the collectivist future of low-ranking chickens to
throw off their chains-- once you have a group of them,
the same traits that could be disadvantageous on an
individual dyadic level, as a group outcompetes
the others. And when you do that, you've
suddenly got group selection in a classical form,
where these animals, because of their traits,
they are not behaving for the good of the group. But the very traits
that are disadvantageous individually are
advantageous as a group. And it's another way
of thinking about this. If you indiscriminately
make low-interest loans to everybody on earth,
you are very readily falling into this category. If you were part of
a group that makes low-interest loans
to each other, suddenly you
outcompete the other. A fascinating book. An evolutionary biologist
named David Sloan Wilson, who's been the main person pushing
for this idea for decades, has a very broad range of
intellectual interests, including religious history. And a number of years
ago, he published a book called Darwin's Cathedral. And he analyzed the birth
of clusters of new religions over time as examples of
founder effects and group selection-type properties. And he wound up,
in great detail, analyzing Calvin and the
starts of Calvinism and Calvin and his sidekick Hobbes in
Zurich in the 17th century, or whenever it was
that Calvinism started, of analyzing how there were all
sorts of these little religions popping up there in
these little city-states. And what it was about
Calvinism-- in I think it was Zurich--
that took off, where they established some
of these inbred cooperative patterns and then
beat the pants off of all the other city-states. And soon, all of central
Europe was Calvinist. Really interesting
book in that regard. OK. So back has come this whole
possibility of group selection. And out of that has come the
more broad way of thinking about it now, which is
multi-level selection, a very important concept here,
which is sometimes selection occurs entirely on the
level of a single gene. In other words, have a gene
with bad enough of a mutation, and it doesn't matter how
many great other genes you got going for you. Selection will be
decided entirely on the basis of one gene. As we saw in our principles
from the other day, much more common-- selection at the
level of the individual, [? at ?] an aggregation of
the genotype playing out in terms of phenotype all
the different traits there. But what this introduces is some
circumstances where selection is at the group level. And it is never at the level of
how an individual's trait plays out individually in a group. It's how this trait
played out individually emerges as a group behavior
that you get group selection. And this marks this
great peace that's come between this
David Sloan Wilson and the guy who's probably
the most towering figure in this whole field,
this guy EO Wilson, Edward O. Wilson at Harvard. David Sloan Wilson and
EO Wilson spent years not getting along with each
other because Wilson-- Wilson-- because EO Wilson
is very strongly individual
selectionist model guy, and thus he hated
group selection. David Sloan Wilson,
the other way around. Each of them were
endlessly invited to the wrong parties because
of the same shared last name and all sorts of social
awkwardness there. In the last few years, I
don't know what happened. I don't know if they
arranged marriages between their
grandchildren or something. But they arranged
some sort of truce. And Wilson-Wilson
published a paper last year basically saying,
whoa, you know what? Some of the time I'm right, and
some of the time he's right. And isn't that great, and
can't we all get along, and delineating circumstances
where individual selection-- individual selection, kin
selection, reciprocal altruism is going to dominate
circumstances where selection is going to get
played out at the group level. They love each other now. They have formed a new language. They share burial customs. And this sort of constitutes
a great resolution. Yeah, depending on
the circumstances, the most important
thing in evolution might be a single gene, a single
organism, or a single group. And the power of a group
and aggregate traits that work lousy in the
individual is going to be really important
down the line when thinking about aggression
and stopping aggression and things of that sort. OK. So all of this is great. This multi-level
selection now showing sort of a fancier,
more sophisticated way of thinking about
individual, kin, reciprocal circumstances,
where it works, circumstances where this is
the most interesting thing. So that's great. So now we begin to look
for a first pass of where humans fit into this. We've already seen in terms of
all of these traits, tournament versus pair bonding, we're
somewhere in between. In terms of imprinted genes,
we're somewhere in between. These are specifics. How do we begin for
a first pass to think about humans, human behavior,
fitting into these frameworks? Two problems, or two
issues, that are all we'll touch on at this point. The first one is, there
is this temptation, as soon as you think along
these lines, to discover, oh, isn't that interesting? Langur monkeys will
have infanticide. Male langur monkeys will kill
the kids of some other male. Human males do that sometimes. Oh, langur monkeys might be an
interesting evolutionary model for where infanticidal
behavior came from in humans. Oh, isn't this interesting? Dominance is passed
along by males. We do that [? sometimes. ?]
isn't it interesting? Kidnapping somehow occurs. And before you know it, you
have a world in which people are saying, well, damselflies do
something that look like rape. So huh, we've got a damselfly
model of human behavior in that realm. And two things are
happening there. One is taking the traits,
a small number of traits, in some other species and
inflating the relevance it has for understanding us. The other danger
is that somewhere, creeping below the
surface, is you see it happens in other species. It's kind of natural. It's kind of inevitable. This is a whole world in
which people have run off with how this applies to humans
in a completely distorted way. We are unique as a species,
as is every other species. We are unique. By applying the same
evolutionary rules that every other species has,
that's the commonality, not the outcome. The other challenge
is constantly going to be that you get all
these great predictive models, and then humans
go and screw it up by having quirks
and idiosyncrasies and personalities
and stuff like that. All I can say in that realm
is, back to Wednesday, if making sense of
which lions are going to go to the scary speaker
in the bushes there revolves, in some part, around
personalities, humans, by the time you get to us,
blindly assuming these models apply is going to be very shaky. OK. So just a first
pass at how one will have to be cautious
for the rest of course in applying all these models. Now, far more critically,
is looking at, what are the criticisms
that have been brought against this whole framework? This framework of
social behavior has evolved to maximize
the number of copies of genes driven by kin,
driven by reciprocal altruism. Group selection is a rare
trait, but when it does, it follows these properties. This is how you explain
all the behavior. Know these four or
five rules and not only can you look at two
skulls of different sizes, but you can explain all behavior
and all of human behavior, and it's all biology. And eventually,
as EO Wilson said in his landmark
book of his in 1975, Social Biology, eventually
all of the social sciences will be under the wing
of evolutionary biology. No surprise that social
scientists were not very pleased with that
proclamation at that point. But this was this
notion that this was going to explain everything. So what are the criticisms
that have been leveled at this style of thinking? And as we'll see, there
are a lot of them. All of the stuff we've
been thinking about, this basic notion of applying
the Darwinian rules as to why giraffe have to have hearts
of certain size to behavior, there's three features that
are coming through [INAUDIBLE]. The first one is the notion
of heritability of traits. Because what we've
been discussing throughout the last
lecture or so is, there's heritability of the
tendency to kidnap infants at the right strategic time. There's heritability
of the tendency to decide that you like
males with big, fancy plumage and long canines. There's heritability to deciding
that your daughter should be highest ranking in
the troop [INAUDIBLE]. Heritability. An assumption of heritable
behavioral traits runs through every single
one of these discussions. The next theme that runs
throughout all of them is the notion of adaptiveness. If some trait has emerged
out of the evolutionary murk, if some trait has
been selected for, selection implies
adaptiveness-- the notion that everything you see has an
adaptive explanation for why it's emerged evolutionarily. The third principle, which
is not explicitly stated in this field very often but
is implicit to everything about it, is these processes
of evolutionary change are gradual. At every generation, if by
getting into some better behavioral strategy for
playing prisoner's dilemma you leave 1% more copies of
your genes than everybody else, come back in 100
zillion generations and that trait will have spread. All of this is played out in
generation after generation so that evolutionary
change is occurring in gradual, incremental steps. So what do you do with
these three starting points? The first one. An awful lot of
the next two weeks will be looking at how
other disciplines look at the issue of, how
do you figure out when a behavior is genetic? And one of the first
things we'll learn is how that phrase means
absolutely nothing whatsoever. Maybe a better way of
stating it is, how do you figure out when a behavioral
trait has a genetic influence? And as we'll see, even
the safer way of saying it is, how do you
figure out in which environment a
certain behavior has a particular genetic influence? How do other disciplines go
about saying, oh, it's genetic. It's genetic. In this field, among this sort
of sociobiological thinking, what you do is an
inverse style of proof. You say, OK, if a trait
has a genetic component, you would expect it to be
heritable along these lines. If it's more adaptive,
it will increase its frequency, all of that. And look, that explains where
competitive infanticide has come from. Show me a more
explanatory model. Show me a model that
is more predictive. And until you can
show me one, I'm assuming this trait
has some heritability. And we'll see how, by next
week, the more molecular people rip this view to shreds. Tell me, when you're
talking about heritability of some behavior,
show me the damn gene. Show me the sequence of DNA. Show me how that
produces the behavior. This is where this field
ends saying, oh, we can inferentially sort of decide
there's a genetic influence. As we'll see by next
week, this one piece is the main thing attacked
by a number of other fields. Next piece, the
adaptiveness-- the notion that everything
that has evolved has evolved under the scalpel
of evolutionary demand for optimization
and all of that. And the critics
of this view call this the adaptationist
fallacy-- the notion that everything is
there for a good reason. And what they often do in terms
of making fun of that is that, oh, you look at people
who do this kind of evolutionary biology with
this adaptationist emphasis, and it's one big just-so story. Why do giraffe have
hearts with thick muscles? And here's the story I make up,
and if my story is better than yours, I get tenure
and you don't. Why is that the
zebras got stripes? Why is it that
males kill infants in this species or whatever? That everything is adaptive. And what you need to do now
is come up with the story to explain why it's adaptive. And if it fits some of those
principles of individual and group, et
cetera, then you win. You've got the
best just-so story. And what is constantly
brought as a sort of criticism of that is, show me experimental
evidence that it is adaptive. And by the time
we get to looking at the field of ethology,
you'll see a whole way in which people do that. Show me that it's
possible to disprove it. OK, tell me a just-so story,
where if that were the case, that would prove that this
is not what's going on. You got to have the
rules of science. It can't just be you observe
something and come up with the best story and you win. But what's most striking in sort
of terms of criticizing this is some domains
in which there are traits that have not evolved
because they are adaptive. They've just evolved because
they are excess baggage. And this has brought in a whole
sort of criticism of the field. Now, some of the time, when
you begin to see-- it's kind of hard to see where
the adaptiveness is. It's because it's a more
subtle feature of it. For example, you
could look at squid. And someone who is
enamored with fish and how cool and aerodynamic,
aquadynamic, fish are and all of that, will
point out that squid are pretty lousy swimmers
compared to all sorts of fish. They're pretty lousy
swimmers compared to fish, but they're pretty great
swimmers for something starting out evolutionarily
as a mollusk. This adaptiveness has to be
in the context of where it came from and where it got to. OK, so that is a qualifier. Nonetheless, even
factoring that in, of hidden features of adaptation
in evolutionary history, there's lots of traits that
are simply not adaptive. And one of the most
effective critics of this whole view,
Stephen Jay Gould, introduced a term about 30 years
ago that summarized this view. Gould was a
paleontologist at Harvard, and his thinking will come
in a whole lot in next week's lectures. He teamed up with another guy, a
molecular geneticist at Harvard named Richard Lewontin. And in critiquing a lot of
this, they came up with a term saying an awful lot
of traits have evolved that exist not because
they're adaptive, but because they're spandrels. So at that point,
everybody in the field had to go run to
their dictionary because Gould and Lewontin were
all being snotty and coming up with fancy, highfalutin
culture terms, because it turns out "spandrel"
is a term from architecture. So immediately, they already
won points off of everyone else for being all
cultured and stuff. But a spandrel, a spandrel is
you got some medieval building. Remarkably enough, that's a
medieval building, and-- [SIGH] [LAUGHTER] --it's a nice medieval building. [LAUGHTER] And what you get is you have
these arches that-- there winds up being a space
between arches, that's there's space between
arches just because you can't build arches
next to each other without there being
like this space here. This is solid brick or
LEGO blocks or whatever. So you have these arches, and
there's a space in between. And you got this space. It's not there for
any good reason. It's there because you can't put
two arches next to each other without coming up with
this triangular space. And the architectural
term for those triangles are "spandrels." And spandrels, in
architecture, is something that forms between two arches. And as Gould and
Lewontin used the term, a spandrel is some
trait that occurs simply as the unavoidable outcome
of some other traits that are being selected for. You can't put two
arches together without getting some sort of
triangular shape in between. And throughout the history of
architects making spandrels, these would be artistically
built up and all of that, and there would be all sorts
of decorative stuff on that. So if you were an adaptationist
[? folly ?] person, everything has an adaptive
[? purpose. ?] You look at that and, oh, there's got to be
some reason why spandrels have evolved and have these elaborate
secondary sexual features on spandrels, little gossamer
things flying around and stuff. And there's got to be
an adapt-- oh, I know, because people in church will
look up at it a whole lot, and their necks will get sore. And when their necks
stop being sore, they will decide this
is the glory of God, and they will increase
their [? belief. ?] That's why architects
put in spandrels. No, you can't build
buildings like this without spandrels happening. And just because
they were there, why not let's decorate them. That's the evolution
of spandrels. And in Gould and
Lewontin's critique, an awful lot of stuff,
where the sociobiology types would sit there and say, we're
going to have a just-so story contest now and
use our principles and figure out some way in
which this is actually adaptive, they're saying, this
actually wasn't selected for because it's adaptive. It was an inadvertent
byproduct of something else. So here's an example
of that would be given. Humans have chins. Humans have chins. Apparently, all
humans do have chins hidden away someplace or other. Humans have chins. And weirdly, we're like
the only primate that does. You look at, like,
other apes and stuff, and they have the
sort of weak chins that suggest sort of immoral
characters and criminality and things like that. We're the only species
that has chins. And apparently, there's been
some like nutty adaptationist school somewhere
back when, trying to make sense of why it is
that humans evolved chins. Why it is that human faces
come to a point there, and what's the
adaptive advantage? And [? where ?] you
can, like, stab rivals-- [LAUGHTER] --or you can get crumbs from
out of the corner on the floor and stuff with your chin. Until somebody figured
out that there's no way that you could
have a primate face that has a muzzle foreshortened
and a jaw at this angle. You do this, and you
do this, and you're going to get this little
spandrel thing sticking out there. And oh, there hasn't
been selection for a chin because you have selection
for a hominid face with a shortened muzzle, and
this thing pops out there. And suddenly, all
those doctoral theses about the reproductive
advantages of chins go down the tubes there. It was merely a spandrel. And Gould and
Lewontin's argument is that there's lots
and lots of spandrels, that this emphasis--
everything is adaptive, everything is the
outcome of competition-- that's produced that,
an awful lot of stuff is excess baggage that
merely gets carried along because the evolutionary process
isn't all that efficient. You're starting with
a mollusk if you want to make yourself a squid. Giving rise to another concept,
another term in the field. Andre Lwoff, who was a
French-- or was it Jacob? They were these two French
molecular biology guys, and they both got Nobel Prizes. And one of them said this,
and I don't remember which, but I'm going to
say it was Lwoff because I like saying Lwoff. Andre Lwoff once said that
"Evolution is not an inventor. Evolution is a tinkerer." It works with
preexisting structures. And the notion that you're
going to see this everywhere, you're gluing stuff together. You're duct taping
this part of the pelvis to this part of the
circulatory system, whatever. And you're going
to have spandrels. An awful lot of
what those folks go through in these whole song
and dances of adaptation are merely spandrels. Evolution is not about
optimizing every single trait. What comes out of
that is this notion that an awful lot of
this world of competition really isn't about competition. You stick with these
models, the models we've been covering
for the last two days, and every bit of
advantage is going to increase the number
of copies of your genes. What's the only
possible outcome? You need to compete. You need to outcompete. It was a critique
of this whole view as being one driven very
strongly by competition, because all the traits
there are driven by having to out-reproduce
the next individual, next individual. Another realm in which
this has been critiqued has been by, interestingly,
evolutionary biologists from the Soviet Union. And where it was
emphasized there-- in Western sort of emphasis
in evolutionary biology, most of evolutionary
selection was about competing with
other individuals. Sexual competition,
competing for running away from the predator faster
than the guy next to you, competing for food, all of that. If you're sitting there
in the Soviet Union and you're thinking about
evolutionary biology, what you're mostly thinking
about is evolving the means of surviving climate
demands, surviving extremes of climate, what would
be categorized as abiotic rather than biotic, abiotic
demands in the environment. And when you look at species
where most of their survival is about surviving
ecological extremes, environmental
extremes, you don't see a whole lot of competition. That's a world with far less. And throughout the years, the
Soviet evolutionary biologists tended to emphasize
abiotic selection, which had far less of an
emphasis on competition. The final piece,
though, the gradualism. The gradualism is very
intrinsic to this. Because if everything
is adaptive, every little bit of
advantage is worth fighting for, and
competition and killing each other's infants and
killing each other's sperms and oviducts and all of that. And every little
bit is going to make for a little bit
of an advantage, and you will have this
gradualist change. And the huge challenge
that came to that was from Gould and another
scientist in the '80s, a notion that maybe that's not
what evolution looks like. Maybe evolution is not
occurring in these gradualist, incremental steps. Maybe what occurs instead
is long periods of nothing happening and then a
rapid evolutionary change. In long periods,
nothing happening, then rapid evolutionary
change, something that they called
punctuated equilibrium. And the whole next lecture
is going to be about this. Critical implications--
the genetics of how stuff evolves
turns out to fit far better the molecular
genetics with these models of punctuated, rapid
change, and stasis, equilibrium, punctuated change,
rather than these gradualist models. And if that's what it looks
like in these steps, most of the time you're
not punching it out for every one-half of
1% reproductive advantage, and it's all competition. Most of the time,
nothing's happening at all, and there's periods of severe
selection and then long periods in which nothing happens. A step function like that,
the role of competition is reduced tremendously in
thinking about evolution. So we're going to
spend a ton of time looking at the punctuated
equilibrium model. To give away the
punch line that I know you are all on the
edge of your seats for, I kind of think it's right
in a lot of the circumstances of evolution because
it fits much better with the molecular biology. Finally, in addition to these
critiques of show me the genes, everything doesn't
have to be adaptive because there are spandrels,
and besides, this is really wimpy science where science
counts as making of the best story, and there's no reason
to think that it's gradual, there's a mechanism
for this as well. In addition to
that, there's always been a final realm of criticism
of this style of thinking, which has been a
political critique. And in lots of
realms of science, you can't really imagine
a political critique as to whether cilia on amoeba
flip this way or that way or a critique as to
whether, like, plants should have three clover
things or four clover things, that there's not a
political factor in that. There's a huge amount of
sociopolitical implications that run through
this entire field. Because it addresses
issues of like how natural, how evolutionarily ancient,
how evolutionarily honed, how adaptive are things like
whether a species, a society, has male domination or not,
has strict hierarchies or not, has certain degrees
of aggression, has certain patterns
of sexual coercion. And a whole world arguing
that these things have a naturalistic grounding in
adaptation versus a whole world that says that's jibberish. Most of the time,
nothing's happening. And when it does, a
lot of it is spandrels. Those have very different
political implications. And from day one, the
critics of this entire world have made a point of
something that initially seems kind of silly,
but may not be silly, which is the entire
founding generation of these sociobiologists
were white, Southern males. Make of that what you will. EO Wilson from Alabama,
Robert Trivers, Irven DeVore, a whole population
of these folks, the first generation
of these people, were all white males
from the American South. Whereas Gould and Lewontin,
all of these guys, were Northeastern Marxists. OK. So we got kind of a
major contrast here. And the critique of the
sociobiological view is, well, isn't it interesting that their
notion of how evolution works just happens to emphasize the
naturalness of a system that rewards them for the
inequalities that we have? Isn't it interesting that their
models predict the naturalness of a world in which they're
the ones who benefit most from the notion that
this is natural? And from day one, that has
been a strong critique. And that's not like critiquing
cilia amoeba theories for political implications. That is a very real one. Because the notions that this
is pertinent to making sense of, is rape a human
psychopathology, or is rape a competitive
strategy, is the fact that children are more likely
to be killed by stepfathers than by biological fathers. Does that represent something
about the typical socioeconomic pressures in families
with step-parents versus the natural biology
of gene competition through competitive infanticide? This has a lot of implications. And from day one, as this
field emerged in the late '70s, there was a huge
political agenda that was assumed to be there. Sufficiently so at one lecture,
a famous conference in 1977 where EO Wilson was presenting
there, a bunch of people rushed the stage and
knocked him off the stage and dumped water
on him and chanted, whatever it is in German,
saying, we will have a society of law and order. This is pretty
agitated circumstances for thinking about science. This was a group in
Boston called Science for the People, which was
a Marxist group at the time there, and saying, all
this sociobiological stuff is doing is justifying a world
in which it is male-dominated, stratified, and where aggression
and competition pays off. And this has been
highly controversial from the beginning. The one counter to it-- and I
think a lot of that was valid, and I think a lot of
it instead defaults into models where this is not
making a whole lot of sense. The one thing to
be pointed out is, when we see what punctuated
equilibrium is about, it's exactly the sort
of world of evolution that produces the sort of world
that a Gould or a Lewontin would want it to be, one
which minimizes competition in favor of cooperation and
a whole pattern of stasis and rapid dialectical change. It's exactly the world that
two Marxist geneticists would say evolution should be about. So I think that as
a first pass, you're seeing this stuff is dripping
in sociopolitical implications. So starting Monday, we will look
at this punctuated equilibrium, taking apart this
piece of the story. And basically, for the rest
of the course, examining-- For more, please visit
us at stanford.edu.
