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programs. ♪ [music] ♪ - [Narrator] We are the paradoxical ape,
bi-pedal, naked, large brain. Long the master of fire, tools, and language, but
still trying to understand ourselves. Aware that death is inevitable, yet filled
with optimism. We grow up slowly. We hand down knowledge. We empathize and deceive.
We shape the future from our shared understanding of the past. CARTA brings
together experts from diverse disciplines to exchange insights on who we are and how
we got here, an exploration made possible by the generosity of humans like you. ♪ [music] ♪ - [Bernard] This is a topic that I have
been thinking about for some time as you can gauge by the difference in hair color
in that picture and now. But what I want to do today is to try and use the
experience of those years to see whether it's taught me anything and also to use
some data from some young people. And I'm very grateful to Eve Boyle and to Andrew
Du and to David Patterson who are all graduate students in the Home Power
Program at the university where I come from. And I'm mentioning Mark Collard here
because he and I worked on this now a little time ago and I'm going to say some
things that he might or might not agree with and I'm just giving him a warning. So
what, what are we looking for? Homo is a genus and when Mark and I started to think
about this, we could not find a definition of a genus that was universally supported.
So we put together, for our own purposes, a working definition of a genus and we
suggested that it was “a species or a monophyletic group whose members occupy a
single adaptive zone. ” Now let me try and unpack some of that. For a species to be
included in a genus, it should belong to the same monophyletic group as the type
species of that genus. Now the type species of a genus Homo is Homo sapiens so
what we argued was that the different species deserve to belong to Homo then it
should be in the same monophyletic group. Now a slightly shorter term for
monophyletic group is the word clade and how do you define a clade? The definition
that we use was “all of the taxa, no more and no less, that are descended from a
recent common ancestor. ” Now I like metaphors from the car industry and so as
not to let my colleagues down, I got some new ones here. The common ancestor of all
Toyotas is a Toyoda, it's a model which was developed in 1935 by a company, the
company originally made machinery to made textiles. So it did not start as a car
company, but they decided that they wanted to make cars and they went to America to
learn how to make cars then they went back to Japan and they made a car, and it was
the A1. So that's the common ancestor of all the models of Toyota that are and have
ever been. So that's what we're looking for. The notion of the second criterion
was that for a species to be included in Homo its adaptive strategy should be
closer to the one of the type species, i.e.modern humans, than to the type
species of any other genus. So the candidate species that we are thinking
about including in the genus Homo, that and the type species should be part of the
same grade. So, what is a grade? It's just a series of questions that I keep... So a
grade is “a group of taxa that shares a suite of what we call adaptive features. ”
So we would suggest that if you do share those features you are in the same
adaptive zone. So back to the cars. So the Toyota Motor
Company decided that it should make a jeep. It saw the success of the Willys
Jeep, it was a four wheel drive car. So it decided to make its own four wheel drive
car. My suggestion is that as soon as you make a four wheel drive car, you are in a
new adaptive zone. You are in a different adaptive zone and this is the one that
they made. And so my contention is that in the Toyota clade, that the BJ which is
what this is, marked the beginning of a new adaptive zone of four wheel drive
vehicles. Now you could argue that hybrid cars might be a new adaptive zone as well.
You could argue that the design of a minivan which was introduced by the Toyota
Motor Company and it was called very imaginatively the first one, it was called
a van. Okay. And then the next model was called the Previa, and the model that
exceeded that was the one that you see now called the Sienna. My contention and my
suggestion is that the notion of a minivan is a new adaptive zone. There are levels
of sophistication. Now the doors open electronically and you can argue that, you
know, does the addition of electronic opening doors make it a new adaptive zone?
That's up to you. My sense is that it's not much different as to whether you open
the door yourself or whether they open electrically and so I wouldn't call that a
different adaptive zone. So here, there are people who are interested in the
evolution of the four wheel drive vehicles made by Toyota. And here is an image that
was very kindly found for me by another graduate student
who is called Alexander Pruca [SP], and you can see that there are people who are
interested in the evolutionary history of the Land Cruiser. And so, they are
interested in what we are interested in. But the problem is but if all the evidence
you had for the evolutionary history of the Toyota was a few fragments, maybe part
of the windshield, a little bit of the wheel, something from the grill, a little
bit of the fender, or something from the hood. And the problem is you didn't even
have the same parts for the different models that you're trying to link. That
gives you a sense of what we are trying to do. We do not have the equivalent of the
luxury of all this information about the models and the developments within the
evolutionary history of the Toyota Land Cruiser. So the second question, what
about the who? The genus Homo was established by Linnaeus way back in the
18th century. And as the years have gone by, more and more taxa have been added and
they have been included in the genus. So initially, the neanderthals were included
and then the taxon called Homo heidelbergensis and then the taxon called
Homo rhodesiensis and then a taxon called Homo soloensis. And maybe the biggest
addition was made by Ernst Mayr during the second World War when he suggested that
the taxa that had been in the genus of the genera, tymantrabus and the genus
phyticantrobus, should be included in Homo. So as the years went by, the genus
Homo became more and more inclusive. The criteria for admission were relaxed.
The initial criterion was you had to have a brain as large as ours. So admitting
Homo neanderthalensis, that wasn't a big, that wasn't a huge deal because they had
large brains, too. But by the time you get to including Homo erectus in Homo you are
admitting that this is a genus that can have individuals that can have brains half
the size of the average modern human. Then in 1964, Louis Leakey and the person of
the Leakeys had recruited to help them interpret the anatomy of their fossils,
Phillip Tobias and John Napier, they published a paper in Nature suggesting
that some fossil that had been found at Olduvai should be included in a new
species and that species name was habilis. But maybe more controversially, they
suggested that that species should be included in Homo. Now that meant relaxing
the criteria even more and the question is, was that process of relaxation, that
last process of relaxation, to what extent did that stay within the definition of a
genus that Mark and I suggested? In other words, is Homo habilis part of the same
clade and is Homo habilis part of the same grade? What we argued in a paper in
Science way back was that we didn't think the evidence was all that strong, but
let's get back to that. So how has this process of progressive inclusivity
affected the grade definition of Homo? This is an extremely speciose
interpretation of the Hominin fossil record. Modern humans are in the top left.
What I call a gray...which I call pre-modern Homo which includes
neanderthals and the heidelbergensis and Homo erectus is in the blue.
And then the hominids that Bill Kimble is going to be talking about, the mustard
colored ones are down in the bottom right. And then there are some rather brownish
ones which are rather like the mustard colored ones except they have extremely
large molars and pre-molars. These are animals with very large mandibles and very
large post canine teeth. So the inclusion of Homo habilis in Homo meant that the
genus Homo would include what I've called pre-modern Homo plus the taxa that have
called transitional homonins on the basis of the findings that Mark and I published
way back in 1999. Now I think that paper was superbly well argued and was extremely
clearly written, but it made hardly any impression on my colleagues. And it's fair
to say that apart from a few discerning and discriminating scientists, most people
still include the taxa Homo habilis and Homo rhodesiensis within the genus Homo.
So that's one way of interepreting the genus Homo. So the origin of the genus
Homo would be how do you explain the appearance of Homo habilis? That's another
way of asking the same question. In which case, you would include Homo habilis and
Homo rhodesiensis which is some people think might be distinct from Homo habilis
but it's a similar sort of organism. You would include them in the dark blue
category, in the dark blue grade. If Mark and I are correct then you would extend
the genus Homo down that far. You would stop at the beginning of Homo erectus. In
which case you would regard Homo habilis and Homo rhodesiensis as not the same
species as the other australopiths but nonetheless, within the same adaptive zone
as the other australopiths. So what has happened since the publication
of the paper in Science that nobody took any notice of in 1999? More fossil
evidence has been found and not only has more fossil evidence...more fossils been
found that the existing fossils have been reanalyzed and reconstructed and so on. So
that's one development. The other development is that we have new data and
there people who are reassessing the existing data which relate to what I call
the functional capacities of these animals. What can we infer about how
dextrous they were? What can we infer about how smart they were? What can we
infer about what they were eating? These are just a few of the publications that
are relevant to this, but I want to talk about the categories of the data that
speak to cognition and some new data that speak to diet. Now in relation to
cognition, these are not new data. Most of the data that were analyzed were the
specimens which were used by Leslie Aiello who's in the audience and she will be
speaking later. And this was a plot which was published in a paper and this was a
paper which looked at the relationship between brain size and other revolutionary
trends. And it was this plot which gave rise to this notion that there was a
burst, there was a period of relatively sudden increase in brain size of the
origin of the genus Homo and then there was another burst of increase in brain
size at the origin of the species Homo sapiens. But these data, the plot looks as
if it is consistent with that interpretation, but the plot represents
each value as one point. And the problem with the plot is that the data are subject
to error. In other words, there is error in the estimation of the endocranial
volume and there is error in the estimation of the age.
So what a bunch of graduate students did led by Andrew Du was to look at these data
again. And so these are the data and it's the other way around, in other words, the
older data are to the left and the younger data on to the right. So theirs are also
point there. But then if you add the error, the error of the age and the error
of the estimation of the endocranial volume, you see that the data look rather
different. Then when you do some very fancy statistics, which I was very tempted
to pretend that I knew what they were but I decided that I wasn't going to pretend
that I knew what they were. And then they tested the data against various modes of
change, random walk, or gradualism, or stasis, or punctuated equilibrium which
was the hypothesis of the relatively sudden increase in brain size, and so on
and so forth. They found that the mode which had much the greatest amount of
support was gradualism. So in other words, the data if you account for the error of
the age and the estimate of the endocranial volume, there is no evidence
of a punctuated event. So how about diet? Well, this is work of David Pattison. And
you can see here that there are three color bands. The australopiths that Bill
is going to be talking about. So you can see they are in the light green band and
then the first of the red columns represents the early evidence for Homo in
the Turkana Basin which is either Homo habilis or it's Homo rhodesiensis. And
then the second of the red columns is the evidence for Homo in the Turkana Basin
which is Homo erectus or Homo ergaster. So if the major grade shift was between the
australopiths and the first red column, you wouldn't expect the first red column
to be where it is because these are carbon isotope values. So there is a shift
between the first red column, in other words, Homo habilis and the second red
column which is Homo erectus. Here is David and he's the one who's
collected these data. So if you look at this plot, you can see the blue squares
are Paranthropus boisei who are living in exactly the same lake basin as what is
alleged to be Homo habilis and widely accepted to be Homo erectus. And there is
no change in isotopic signal or the Paranthropus boisei individuals, but there
is a change in isotopic signal for Homo. So there is a more C3 signal for Homo
habilis and then there is a significantly different, more C4 signal for Homo
erectus. You might say, "Well, that's just because the environment was changing and
everything was changing and Paranthropus boisei was the only large mammal that
wasn't changing." Well, that's not true. If you look at all the other large
mammals, they don't change and Paranthropus boisei doesn't change, it's
just Homo that does. So there is a dietary shift from Homo habilis to Homo erectus
and the isotopic signal for the diet of Homo habilis is no different from the
isotopic signals of the creatures that proceeded it and we call australopiths. So
my suggestion is that we just should not assume that the interesting things were
happening around the appearance of Homo habilis. My suggestion is no different
from the suggestion we made in the paper in 1999, that most of the action is around
the appearance of Homo erectus and it's not around the appearance of Homo habilis.
Thank you very much. ♪ [music] ♪ - [Carol] What I'm going to do is either
it can be considered as a sobriety checkpoint or something completely crazy,
but I've been given some might consider the enviable task of talking about the
evolution of early human body form and particularly in the context of
understanding shapes of everything from the neck down associated with the origins
of genus Homo. Now we have this idea about the transition from australopithecus to
Homo. When we look at australopith skeletons we see they're different from
ours. They tend to be smaller in body size, males are much, much larger than
females. We tend to see that they seemed to have shorter lower limbs, longer upper
limbs. They have longer, more curved fingers and toes. They look pretty
different in body form and we have the idea that to go from something like an
australopith to something like us involved a series of changes that we see when we
make a comparison like this. And sure enough, when we look at some of the early
Homo erectus fossils like this beautiful Turkana boy from Kenya, he's about 1.6
million years old. We see that he also seems to share some of those features of
the post cranial skeleton that we see in humans and that he seems to have more
human-like limb proportions with longer stronger legs, bigger lower limb joints,
smaller upper limbs, thinner body form. So this transition has shaped our ideas about
what the adaptive changes would have been to go from point A to point B. Because
after all, if we're trying to understand why and how our genus evolved, we need to
know what changes happened. Did they happen together? Did they happen as a
package, were some of the features evolving at different times in different
places? Those are the data that we have to come up with our ideas about why it all
happened. So when we look at something like this, we see australopiths here. They
sort of had the stocky ape shape. They're maybe living partly in the trees. And then
we have these more savanna-dwelling, animals that may have been doing long
distance walking and running, using fancy pants stone tools, all kinds of things.
But in terms of the post cranial skeleton, some of the features that we think of with
this transition that fuels our adaptive ideas is have to do with changes in limb
proportions, changes in lower limb joint size, changes in the shape of the torso,
changes in body size and dimorphism or difference between males and females.
So what I'd like to do today is take you through a little bit of the evidence we
have and there's only a little bit to talk about so I won't be up here very long, to
see first of all was australopithecus different from what we think of as Homo as
we thought. And I'm also going to talk a little bit about what we have from the
earliest part of the Homo fossil record in the way of post cranial bones that may
tell us something about what was happening. So we'll start with
australopiths because that's the easy part, we have more fossils. If you open up
any human evolution textbook you'll see a picture something like this where you look
at the body shape of the torso of australopithecus and you see this
reconstruction. This is based on fossils done 35 or 40 years ago. There are more
fossils that have come in to change our ideas a little bit. But you see, the
stocky anamode with this cone shaped rib cage. If you connect the dots there and
imagine the belly of this. Big belly, very stiff and immovable and this would shape
our ideas of locomotion and how these things moved around and maybe even
digestive biology and so forth. Well, we know from a whole lot of fossils that this
probably is no longer really an accurate way to look at things. We have a number of
different vertebral columns that show that the characteristic curvatures in the human
vertebral column that holds us upright were present in early australopithecus.
There are lots of vertebrae in the lower back so they can stand up fully upright.
So they're not that ape-like that way. And there are new fossils that are bringing
new bits of data and I'll show you one of those bits of data. This is a skeleton
called Kadanuumu, it means big man. It's an australopithecus male and he's nice and
big. And we're very excited, those of us who care about ribs are very excited
because it actually has some ribs. And you can measure the curvature of those ribs to
say something about what maybe the rib cage would have been like. And you see,
apes have this cone shaped rib cage of very sort of straight ribs. Humans' curve
around, give you this more slender barrel shape rib cage. You can measure this in
Kadanuumu and you can see it's right down here with humans and gibbons who also have
this rib cage shape. Very different from something we see in great apes and data
like these are giving us the picture that in fact the body shape of australopithecus
may not have been so different from our own as we had long thought.
We also can take a look at limb length. We have this idea that australophitecus has
more ape-like limb proportions, longer upper limbs, smaller lower limbs. Based
partly on good old Lucy here, Lucy is teeny tiny so this is lower limb to upper
limb. You can pretty much pick your favorite measure, it doesn't much matter.
And you can see that chimps and gorillas here have bigger upper limbs than humans
for their lower limb size and Lucy seemed to fit that picture. But new data like
these ones showed here again from Kadanuumu show that once you get larger
and fat, australopithecus don't really have very short legs. They maybe have
longer arms, but they don't really have short legs. And Trent Holiday and other
people have done similar analyses to suggest that maybe the lower limbs weren't
that much shorter than australopiths, they're just littler animals. So they may
not be as big a change in limb length from australopiths to Homo as we have thought.
Another thing we've learned recently comes from the foot. An ape has a foot with not
just a grasping big toe, but the whole thing is flexible, so it can wrap around
branches and hang on in the trees. Whereas our feet are very stiff and they form a
nice propulsive lever to move us forward when we walk on the ground on two feet,
and that propulsive lever is supported by arches that go from front to back and side
to side that are built into the structure of the bones of our foot. So one we lift
our heels off the ground, they stiffen up and they let us work well. We've known for
a long time from fossil footprints that australopithecus did not have a grasping
big toe. But recently, Bill Kimble and his colleagues found this bone from the middle
part of the foot, it's called a metatarsal and it shows us that the australopith
foot, just like what we see with maybe Homo habilis or Homo erectus, had nicely
developed arches from front to back and side to side, a fully modern human foot
really well adapted for long distance travel on the ground. So this isn't really
maybe as different as we would have thought a long time...or a number of years
ago as a difference between australopithecus and human.
And if you blow up an australopith to be about the same size you see this really
fairly human-like lower limb, fairly human like body shape, and some of the other
differences maybe a little bit less dramatic than we thought. So maybe this
transition isn't as dramatic as we thought from the australopith side. What can we
now say about early Homo? We have now 2.8 million years ago we see the genus Homo
appear based on this jaw. That's only a couple of hundred thousand years after
Lucy was roaming Ethiopia and it's a long time ago, but it's just a jaw. I'm going
to talk about the post cranial fossils associated with the origin of Homo. Right,
I'm done now. Thank you, have a nice day. I'm out. So let's take a look at what we
actually have. We have quite a number starting around two million years ago.
There are a whole lot of isolated post cranial bones, bits of thigh and arm and
this and that and they're great. But without heads and teeth we can't tell what
species they belong to. So they're not as useful to us as we'd like. What about Homo
erectus? Well, when we find bones that are associated with the heads and teeth we can
tell what species they belong to. These are three skeletons and as you see as you
move over this way, I'm using the term pretty liberally, associated bones of Homo
erectus from the beautiful Turkana boy 1808, 803 from Koobi Fora. But these are
all about a million and a half years ago. That's over a million years after the
origins of the genus. The Dmanisi fossils are a little bit older, 1.8, but that's
still a million years after the origin of the genus Homo. Well, what about the other
early Homo species, habilis and rudolfensis? These are the associated
skeletons we have for habilis. Looks a bit like they were hit with an artillery
barrage, somewhat underwhelming but they're a little bit older. Koobi 42.0,
Olduvai Gorge 1.8. There are some post crania from the type side of Homo habilis.
The association with actual habilis has been questioned by some people so they're
a little bit less certain in terms of their taxonomic assignments but they are
there too, so we have some of those. What about Homo rudolfensis post crania?
That's all we've got, right? We know absolutely nothing about its skeleton
which is unfortunate. And so this whole exercise is a bit like trying to squeeze
blood from turnips which either means it's really, really hard or it means I can make
anything up and there's no data to falsify it. That's all fine, too. But what can we
actually say about that supposed set of characters that may seem to have gone
together with the origin of Homo. Well, we can take a look at maybe body size and
Mark Rabowski and colleagues published some new body size estimates and is there
really a difference between australopiths and Homo? Well, when we look at
australopithecuses we see there's a pretty good range in body size. They're not
particularly large, they're all fairly similar. And when we look at Homo habilis
just a little bit more recent in time, we only have a couple of specimens but they
fall right in that australopith range; not particularly large. When we look at some
of these Homo erectus fossils that we know are Homo erectus, even the Dmanisi
sample's really about similar to australopithecus, you start to get a
little bit larger individuals but remember again this is 1.5 million years ago. This
isn't very early in the evolution of the genus. And so maybe we're saying, "Ah,
here's one that's trended increasing body size happens." But we can look at the size
of some of these isolated fossils and here's a fossil I'm going to talk about a
bit. It's a partial pelvis called 3228. It was from somebody who is about as big as
the Turkana boy and it was 1.9 million years ago. So what can we say about this?
There doesn't seem to be a great trend in early evolution of Homo in either range of
body sizes or absolute body sizes. So we're not seeing anything really dramatic
happening early in the origin of the genus with body size and dimorphism. Well, what about limb proportions and body
build? Well, when you're looking at the oldest things like habilis it's a little
hard to do limb proportions when they're pretty fragmentary. But what Chris Russell
was able to do is instead of looking at bone length he was able to look at the
bone strength. And if you compare it to chimp, you take
the leg to the arm here and you see they're pretty similar in strength. They
plot out about like this. Humans, the lower limbs are stronger than the upper
limbs so they plot out up here. And he was able to take these measurements for at
least the OH 62, the one in black here, and put them on the graph with some Homo
erectuses and what you see is these two Homo erectus skeletons are very human-like
in their strength proportions, but Homo habilis is not. Homo habilis seems to have
a different build. And actually when you take the very few measurements you could
take on this scrappy specimen, it also seems to have a little bit larger upper
limbs relative to lower limbs than we tend to see in humans and maybe in these Homo
erectus. The Dmanisi sample, interestingly, doesn't seem to have the
sort of proportions. It seems to be more like the erectus although the same studies
haven't been done. So there seems to be some sort of a difference here between
habilis and erectus perhaps in body proportion, given how fragmentary the
fossil evidence is. This is an interesting fossil I want to mention because Meave
Leakey and her colleagues found this in 2009, actually fit on this bit was found
in 1980 which is kind of cool. And it's associated piece of pelvis and femur, but
this captures the hip joint. And the hip joint is interesting partly because we
have a bunch of them in the fossil record but partly because the hip joint seems to
be a place that there isn't a lot of difference among these early Homo species
as best we can say. Here's athe3228 pelvis again. In this pelvis shows a series of
features that we only see in humans, we never see in australopithecus, so it's not
a bad hypothesis for a Homo. These two are almost dead ringers for one another but
this one is just much smaller. So either these are a male and female of a really
dimorphic species or they're two species that happen to look the same. But they're
both 1.9 million years old so they're nice and early. Well, when we look at those
Homo-like features, we see them in this 5881, pardon me, this new specimen here.
So here's Lucy and you look at the front border of the ileum, part of the pelvis
it's straight and every australopith we have is bent in every Homo that we have
and it's bent in 5881. When we look at the ileum from the side you could see this
buttress called the iliac pillar here is more vertical and set back from the edge
of the bone and it's big. In the Homo pelvises, it's very weak in every
australopith and angled right into the front of the bone. In 5881 here is looking
like Homo. So this looks kind of like a Homo sort of a creature. When we look at
the other side of the hip joint at the proximal femur, every time you see an
australopith that has a relatively small femural head. So relatively small hip
joint. You see that in the pelvis too, where Homo, including modern humans, have
a much a larger femural head. 5881 needs a little bit of digital reconstruction which
you can do actually for quite accurately using CAD software, it also would have had
a large femural head, and we can see them in the pelvis too. And it's interesting
that every femur we have that seems to be Homo, attributed or not, has a big femural
head. In every australopithecus we have which is associated with post cranials has
a small one. So this seems to be a feature that characterize all Homo, not related
perhaps to body proportions. So changes in body proportion, change in hip joint size
don't seem to co-occur in early Homo. Well, again, squeezing blood out of more
turnips here, we can come back to our bone cross sectional shape. And this is more
work by Chris Ruff Mosley, so you can take a femur, you can slice it open in the
middle and you can look at these sections. And everything we have that we know or
suspect is Home erectus, actual Homo erectus that we have data for has this mid
shaft femur is very wide from side to side and short from front to back. And it has a
really indistinct marking on the back of the femur for attachment of muscles. When
you put Homo habilis on there, it's a very different shape; rounder and it's longer
from front to back. 5881 is a dead ringer for OH 62 in this feature and they both
also have this big, thick attachment here for those thigh muscles.
So, ah, you say, maybe this is Homo habilis, maybe 5881 is habilis, that's
great. But if you put data that Phil Whitemyer kindly lent me from the Dmanisi
skeletons, they are actually shaped like the habilis also. Now either this says
that Dmanisi is not Homo erectus which I really wouldn't want to say based on one
character here, or something else is going on. Chris Roth's idea about the
explanation for these differences is that in Homo erectus, when the pelvis gets
bigger to accommodate larger brains, the whole body gets wider and that puts more
medialateral bending stresses on the bone and so they're wider to accommodate that.
So that this shape would indicate a narrower body form than this shape. Well,
we can look at little bit of pelvic shape and turn 5881. You can take this curvature
here which gives you a little bit of an idea of the inlet. You could see
australopithecus very wide, a little wider in Homo erectus and then these are later
Homo things, but 5881 it seems to be narrower, which seems to fit with Chris'
hypothesis about the explanation for the femural bone shapes. In which case,
perhaps then, Dmanisi may have had a narrower shape than we see in East African
Homo erectus. Does this mean it's not Homo erectus? It's hard to say. Remember that
Dmanisi individuals are 300,000 years older than the Homo erectus individuals I
have on this graph. That's a long time. Think about what happened in the
neanderthals and humans in the last 50,000 or 100,000 years. So this could be
something happening through time. It could be species related. It's very hard to say
given how scrappy the fossil evidence is. But it does say that some of these
characters aren't necessarily co-varying and there seem to be different morphotypes
within the genus Homo. All Homo doesn't look like all the other Homo from the neck
down. And that's an important factor to think about when we then constructing our
adaptive explanations for what's going on in this transition from australopithecus
to Homo. So we have these creatures that may be not quite as stocky as we thought.
The lower limbs may have been much better adapted for decent amounts or quality of
travel while on the ground, and they may not have been as ape like as
we've previously thought with australopithecus. When we look at the
earliest Homo, we may see at least some that may have even more apey limb
proportions than we see in australopithecus. We see that the
combination of features of having larger lower limb joints, of having larger limb
joints, longer lower limbs don't necessarily co-vary. Limbs were already
long, hip joints may have been gotten big at the beginning of Homo, it's hard to
say. Body form may have evolved differently in different species and/or at
different times. But we no longer have this idea of one change associated with
the origin of the genus. And these well adapted features that we see here that
make this complex, that make Homo erectus great that do things like hunting and tool
using and everything later, may be something that weren't associated with the
origin of the genus but came in much later. So in fact, if we compare
australopithecus to earliest Homo, this might be a more reasonable picture to have
in our mind. Animals that weren't really very different especially from the neck
down, weren't really different in locomotor capabilities. If I had more
reconstructions of different Homo species you might have seen them look a little bit
different from one another. But basically, the picture is that there's not a dramatic
change here in the origin of Homo that has anything to do with the post cranial
skeleton. Perhaps the adaptive changes associated with the origin of the genus
had to do more with diet, other behaviors or something else. And that's what we need
to be thinking that what happened to the origin of Homo to give rise to all the
other great things that we've been hearing about today. I say thank you. ♪ [music] ♪ - [Leslie] So, one thing that I sort of
noticed this afternoon is the number of times some of my earlier workers have been
criticized and that's good, that's normal. It shows how the field is growing and
developing and building. And I've been asked to talk about the evolution of human
life history patterns. And this is also a reasonably new approach to study in human
evolution and we can understand a lot about the evolution of the genus Homo by
looking at life history and by looking at modern people. So basically, life history
is more than just looking at the evolution of the physical body form. What it is is
looking at how we got to this body form. Life history is your tempo and mode of
growth and development. And if you look across the primates, you'll find a variety
of different patterns. And if we delve a little bit into life history, as I said,
we can learn a tremendous amount about ourselves. And it starts out in childhood.
You have a difference in the growth and development pattern that's very obvious.
For example, chimpanzees all mature by the time they're about 12 years old. For
humans it takes up until your late teens, 17, 18 years old. And our colleague, Barry
Bogan, has been very clear about the tempo differences that you have if you compare a
chimpanzee with a human. The chimpanzee graph there shows that you have a rapid
decline in the velocity of growth. A relatively small plateau period, that's
the juvenile period. And then another relatively rapid decline in how fast
you're growing. Humans are very different in the corner. We have that same decline
in the velocity of growth but we have a much longer plateau period where our
children are not growing very rapidly. And this is followed by the adolescent growth
spurt and then it falls off again. This pattern is very unique and it's very
important to our evolution. The last graph is from the work of Kristin
Hawkes who's here in the audience. It shows you not only do you have the
difference in the pattern of the growth but we also have a very much longer
longevity or life span. Now what I find fascinating particularly about the early
childhood growth is that it has a lot to do with the brain. We know that humans
have brain sizes about three times the size of a chimpanzee and that brain grows
and develops at different paces in the two species. Now in humans, as a child is
growing, a very young child with a huge head uses about 60% of the energy budget
just to support that brain size. And as we grow and our body begins to grow, the
brain growth slows down and the energy balance tips. One of our colleagues, Chris
Kozawa, has come up with I think is a brilliant look at the relationship between
this brain growth and body growth. In these graphs, the red line, one for males,
the second graph for females. The red shows the energy that the brain takes as
you move from birth up through five years of age that is one of the most energy
expensive periods of brain growth in childhood because of all the mileazation
that's going on and then it drops off. The blue line is the velocity of your somatic
growth, your body growth. So basically there's almost a perfect play off between
brain growth and somatic growth. And this goes terribly long ways to explaining why
we have this extended period of childhood that basically correlates and is a
necessary correlate in energetic terms with the growth and development of the
large human brain cells. Now we all may think this is fine and good
but it's actually not. So some of our other colleagues from Switzerland, Karin
Isler and Carel van Schaik have developed something they called the gray ceiling.
And what the importance of this is you can just take so long in your growth and
development or you aren't going to be able to replace your population size. Now think
in terms of dependent childhood and if a child is dependent on a mother for five
years, six years, seven years, she's going to come back into fertility. You're going
to extend that inter birth interval. You aren't going to be able to have enough
surviving children to replace your population from one generation to another
generation. Okay, this is what they call the gray ceiling. And if you look at the
graph here, there is a lot of primates. The red dots are the apes with the
increasing brain size. And what this shows is that with some of our apes like the
orangutans, the gorillas and all, what they're arguing is they're hitting the
gray ceiling and the only way to avoid that gray ceiling is to somehow increase
your reproductive output. Now if we go back to that same little chart I chose
earlier, at the bottom is the period of infancy. And in chimpanzees, infants are
dependent on their mother, they're still nursing. They are four to four and a half
years old before they're weaned. In humans, it's of course very much shorter
and this particular graph shows about two years, it varies. But what the take home
message of this is is you can have twice as many kids if you shorten that period of
infancy. And if you then shorten your interval
between birth. Now again you may think this is fine, this is a good trick, we've
all developed it, but it has tremendous problems. And I've got this picture
hanging in my office and whenever I think I'm having a hard day I think of her.
Because what you have once you start to double up this is you have a woman who may
be pregnant. The infant that she's probably in the last stage of nursing and
a dependent kid. And she has to get the food to support her own large body weight,
her own large brain size, and to provide all of the calories for the kids she's
nursing. She has to provide the food for the young infant. Now this is very
different from what we see in the chimpanzees or other apes where mothers
focus on one infant. And once the infant has stopped nursing they will gather their
own food. There's very little energetic involvement with the mother. Now this is a
huge paradox and this is where the evolution of sharing and cooperation comes
in. And of course this is where we have the grandmother hypothesis and the
argument that a lot of the extra resources for the grandkids come from the
grandmother by provisioning the mother and the kids. Now there's a number of other
arguments also that involved greater cooperation among all individuals in the
society, males as well as sibling care and sibling cooperation. The take home message
is that once you begin to develop a large brain size, you have growth and
development implications. And these growth and development
implications have implications for the evolution of what we would recognize as a
human type of cooperative social organization. Okay, the big question is,
can we tell when this all happened in human evolution? And we'd like to think,
oh, this is a characteristic of the root of the genus Homo, that's a hypothesis.
Now if we go back to the evolutionary tree, we have one way into this in terms
of cooperation. And if we go back to the gray ceiling and I know Burden isn't going
to like my brain size against a million year graph. But if we put the gray ceiling
onto this and again what Isler and van Schaik argue is that gray ceiling is about
700 milliliters. Now of course there is, you know, big ranges of variation around
this, but what's interesting about this is this just about divides our Homo erectus
from the earlier hominids. And if we put it on our evolutionary tree here, it comes
at this very interesting time between two million and one million years ago where
you have a proliferation of hominids, a variety of different species, and you have
this big variation in the brain sizes that we have. Now as we've also heard, this
time period correlates with the radical change in human adaptation. And
particularly in evidence for the precedence of animal based tissues in the
diet, it also correlates again with our Turkana boy here and this general time
period where you have the evolution of what we call Homo erectus. Now what's
interesting about this also is it also correlates with the time period where
hominids begin to move out of Africa. So our question here is how much does this
cooperative behavior that we can infer from the brain size and we can refer from
the life history really affect the hominid's ability to adapt to a variety of
different habitats not only in Africa but also throughout the world? Now the only
direct evidence we have for any type of cooperation comes from the side of Dmanisi
and our friend here with no teeth. And I'm sure it feels very familiar with the
argument that this individual must have whatever you want to argue, been taken
care of. The message from this is we don't really know how to recognize this
cooperation in the fossil record. It would be very nice if we could. Now if we come
back to the fossils, is there any way from the fossils we could tell what their tempo
of growth is? And in this case, one of our colleagues, Chris Dean, has been working
on how to infer growth and development from the formation of the teeth. I've been
very impressed by some recent work by Chris and his colleague, Helen Livesidge
in London. Not on teeth this time in particular, but on body size because what
Chris has done is sort of bracketed the age of our Turkana boy at death to
somewhere between seven and eight years old. Now what these graph show were really
startling to me because the green one is stature. And the histogram is the stature
of modern human kids who are between about 7 and 10 years old. The red line there is
the estimate for the Turkana boy. It's way in excess of the stature that you would
expect. The blue is body mass or body weight. Again way outside of what you
would expect in modern human kids. Now what does this tell you about the
growth and development of the Turkana boy? If we go back to Barry Bogan's figures,
what it's telling you is that the Turkana boy was growing on a trend very much more
similar to the apes than to modern humans. And if you look on the chart, in fact just
above age there on the chimp chart is eight years old. And you've come out of
that plateau of slow growth velocity, the individual would be then growing towards
his adult weight. In humans, it would be still well within that plateau before that
growth explosion, that's the adolescent growth spurt. Now this, to me, is very
convincing evidence that the Turkana boy was not growing and developing on the
human pattern. Now what that would mean is that it would reach maturity much more
rapidly than if it was growing on the modern human sort of tempo and mode. Now
is there anything more we can tell? Your eruption of teeth tends to still also
measure how long your growth period is. And what's become very clear recently is
there's a tremendous amount of overlap not only between living human tooth eruption
and tooth formation patterns and apes, but also overlap in the fossil hominids. And
when it comes down to it, if you're looking at tooth formation, your best
tooth in terms of distinguishing us between the chimps and humans is your
third molar. But again the take home message from this comes in the bottom
graph. And the blue line there is the tooth development for your second premolar
and that's in the chimps, the red one is in humans.
The vertical lines are your early Homo fossils. The green one is the Turkana boy.
And although the teeth are developing at the very, very fast end of modern humans
and there's a tremendous amount of variation, it's squarely within the ape
pattern as well. And if we're going to argue about what the life history patterns
of some of these early Homo are, basically we're talking about a much more ape-like
growth and development pattern than a human-like growth and development pattern.
Okay, the next questions comes in is when did we start to grow and develop as
humans? And the first indication is with Homo antecessor which is about a million,
not .9 million years old. The teeth are still developing more rapidly than ours,
meaning they're developing more rapidly. But the argument is made that the first
ones that are closer to modern humans than to the early Homo, the early
australopithecine pattern. And then as we move up to the top at about a 160,000
years ago at the Moroccan side of Jebel Irhoud and this is some of some John Jack
Hublin's and his group right there in the fourth row, where you have a very modern
human growth and development pattern. Now what I want to do is sort of finish with
what is probably everybody's favorite fossil and that's the neanderthals. And
they're a long way up the record from what we're talking about in the evolution of
the genus Homo. But I think the lessons we can learn from the neanderthal growth and
development, we can usefully bring down the record and apply to some of the
australopithecines. Now neanderthals of course are the
alternatives to modern humans. They have brain sizes that overlap with ours. They
are in the blue series of Xes there. They lived in Europe during the last ice age
while anatomically modern humans were evolving elsewhere in Africa. What, again,
another piece of evidence that struck me that comes out of Martin Gonzales and some
of his colleagues' work from Spain is the growth and development of the little
neanderthal kids. So the blue lines here are your growth from not years, up to 70
months. The horizontal lines are the equivalently aged neanderthals in relation
to that modern human growth pattern. So here you can say the little neanderthals
are basically plateauing much earlier than you would see in the human growth curve.
Now think about being a neanderthal. I'm often happy I wasn't born a neanderthal
because, you know, what the authors are arguing here is not only do they have the
energetic stress of growing and developing that large human-like brain size, they
also have a serious thermoregulatory problem. Because in fact with Steve
Churchlin I've done some modeling on the energetic requirements in neanderthals and
it's about the same as to say somebody riding the Tour de France in the Alps.
It's about 500 kilocalories a day. And you think of these poor little neanderthals
trying to support that brain and also keep warm. Now there is a second piece also
that comes from other research. This is from Smith et al in 2010. And the
green lines here are your expected and predicted ages for human teeth and the
blue lines are the neanderthals. The take home message is their teeth are developing
more rapidly so they have a more attenuated growth and development process.
Now coming back to this and where you would expect to say a modern human
populations to have more rapid growth and development. It's in situations where you
have a higher mortality rate. Now think about these poor neanderthals, they have a
very high mortality rate, every three calistosis. It's the same as rodeo riders
in the southwest. And you have these poor little stressed neanderthals with a
shorter body size. Now if we come back to all of our, you know, fossil species, our
australopithecines and early Homo, living in a period of very fluctuating climate in
Africa, and this little zig-zag chart is just from East Africa, but also
experiencing all of these environments around the world. What we really want to
know is what their growth and development patterns are and how these reflect what's
happening in their lifestyle. And what I tend to think is that the same processes
that affect us today were also affecting them. And this is a huge challenge, it's
very exciting research and I think as soon as we're able to screw down into it, we're
going to find similar neanderthal-like patterns among the hominids that are
living different types of lifestyles. To end, I'd like to thank CARTA.
We were all having a great time here. And I'd particularly like to thank all of the
attendees of a Wandergrand conference, some of you are sitting in the audience
here, that we held on human biology and the origins of Homo. And a lot of these
life history ideas were developed in a week-long meeting in Portugal. So thank
you very much. ♪ [music] ♪
