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by the generosity of humans like you. - [Peter] So I've been spending some
time working on this question about the role of climate change
in early human evolution. I think that the best way to frame it is that our best
understanding of this problem is really it's this relationship between climate and
life. That is how has climate shaped life and how's life shaped climate? I think the
best way to convince ourselves that this is something that's in our blood, in our
entire world is to look at a seasonal map of primary productivity in the oceans and
on land. Over a multiple year period you can see the waxing and the waning of
growth on the planet following the seasons. The planet literally breaths with
life that's paced by just the tilt of our earth with respect to the point of
its orbit around the sun. Also if we take the longest possible perspective we also
find that climate shapes life. Each of the five major mass extinctions in life on
earth over the last 500 plus million years, each of those five has been
associated with a change in the environment. And each one of these red
lines here are where the mass extinctions occurred. Where somewhere between 50% and
90% of all species that were alive at the time became extinct. There are some who
have argued that there should be another red line there for today. The last
extinction was the extinction of the dinosaurs and that paved the way for the
rise of mammals. Today I'm going to be talking about this last little sliver
of time that includes our history. If we look at this history of human evolution
this is a greatly simplified diagram of the human phylogeny or the family tree.
You can basically see this sort of red, yellow and green sections. The human
family tree is sometimes been likened to a Y-shaped pattern or a more bushy one if
you're more of a... not so much of a lumper. So we move from a single very
long-lived lineage of Australopithecines up until about somewhere around 3 million
years ago where the family tree takes's a branch. One lineage the yellow is
sometimes referred to as the Paranthropus. They are sought of the line backers of the
human family tree. They ultimately were not successful. Then the blue lineage
which is our own. That is the genus Homo. It's been described actually Rick Potts
and I were part of a national research council committee to evaluate
these main times of human evolution. It appeared there are two main periods where
there's a lot of action going on focused intervals of time. This includes this time
interval from about 3 million to about 2.6 million years ago when there are at least
several things that are happening at this time. The extinction of Australopithecus
afarensis otherwise known as Lucy. Also the appearance of these two lineages our
Genus Homo and the Genus Paranthropus Then this is also when the first
stone tools appear. Some time along 3 million years ago. Then another event
occurs sometime just after 2 million years ago. Where we see the appearance or the
extinction of early Homo, the emergence of Homo erectus. The first time we start
seeing the acheulean tool kit which is a much more sophisticated tool kit that
would become the model for future stone tools. Then this is also the first out of
Africa. This is the first time our ancestors left the African continent. It
was about 1.8 million years ago. The point of my discussion today is to ask this
question if climate is shaping life did it also shape human origins? The question
here really is not so much just asking this question did climate shape life, does
shape human evolution but you really have to ask the primary question which is how
did African climate change? That turns out to be a really challenging problem for a
number of very reasonable reasons. I will let you know that the aim of this talk is
really to illuminate these two main ways that African climate has changed in the
past. One is that there have been this very regular pendulum swings if you will.
Very rapid in geologic times, roughly every 20,000 years where African climate
oscillated between wet and drier conditions. It's been like a pace maker
throughout millions millions of years. The other thing that's happened super imposed
on these wet dry cycles is this long term shift toward more open air conditions. If
you allow your mind's eye to envision East Africa right now you probably thinking
about the Serengeti or these open fields of glasses. That ecosystem is actually a
geologically very recent phenomena only a couple of million years old. When we look
at the past African climate change we see that variations in the strength of the
African monsoon have been paced by variations in orbital procession. This is
basically that the earth has a wobbling in its orbit. Our northern hemisphere, our
star Polaris right now the orbiting star 10,000 years ago was actually the star of
Vega. Which is about forty seven and a half degrees of in the other direction.
The earth's rotational axis swipes out a cone in the celestial sphere on the 20,000
year beat. What that does on earth is it changes the seasonal distribution of
sunlight such that over Africa the northern hemisphere summers would have
been about 7% more sunlight in the winter that had exactly the amount less. What
this means for Africa is that it's strengthens; it invigorates the African
monsoon with 20,000 year beat. It acts really like a volume knob on the
strength of the monsoon. These intervals in green that are shown here would be
times of what we call an African humid period. A time when it would have been
wetter in the past. You'll see that they would have been paced at this 20 year beat
throughout this time period. Now we know this is actually true. So this actually
predicted from theory and what amazing and this is one for the reasons why I work in
this field is that when we look at the geological record for this it shows that
they were this wet periods in the time. This is actually from the sediment core in
the eastern Mediterranean where a sediment core was drilled in this location. This is
a 10 meter core. This is one and a half meters and it connects with the top up
there. The base of this connects to the top of there and so on. You can see it has
these black and white layers. The black layers are these organic sediments that
accumulated when the Nile River outflows much much greater than today. So that made
for anoxic or low oxygen conditions in the bottom of the Mediterranean. Just like if
you turn off the bubbler in your fish tank all the fish die and the organic
matter goes to the bottom that's what happened during each one of these events.
It happens not only for this time period here representing maybe 200,000 years of
time but actually for millions of years. This actually an outcrop that we see in
Sicily. It's actually a shot from a bar in Sicily. These are actually people working
on this outcrop. You can barely see that little red dot. In each of these dark
layers is one of these self sapropel units. You can see how they are
bundled into groups of four and five which is this eccentricity modulation of these
processional cycles. Each one of these dark layers will get 20,000 years apart.
This represents one million years of time going back 10 million years ago. So this
has just been a heartbeat of African climate change going on for millions and
millions of years unbroken. If we look at Lake Turkana for example. Lake Turkana in
northern Kenya is nestled in a desert environment today but if you go to the
shores of lake Turkana you'll see this bathtub rings where lake Turkana was 50
meters or 150 feet higher than it is today during one of these wet phases 10,000
years ago. That's just one of these little bars at the very top. You can see they've
been just hundreds of these in the past. African climate has been nothing but
continuously varying between wet and dry and wet and dry. So we look at the
grassland expansion. This is the second way that African climate has changed over
the time scale of early human evolution. Again I show you this image of these
grasslands from East Africa. These actually cover something between 80% and
90% of the East African landscape today. These envision of let's say the Serengeti
this vision that we all have of East Africa is actually very recent geological
development, only about two to three million years old. What's interesting
about this savannah grassland is that they represent a very specific ecological
adaptation to a very specific environment. That environment is hot, dry, very
seasonal rainfall, and low carbon dioxide. In fact the photosynthetic pathway that...
This is called C4 because it represents the four carbon compounds that's developed
through photosynthesis verses a three carbon compound. The C4 molecules or the
C4 photosynthesis is adapted to very high temperatures and low atmospheric CO2 and
generally dry conditions. So these constitute the tropical grasses that
dominate Africa particularly East Africa today. They are there because the
environment is very harsh. It's dry and seasonally moist. Only moist seasonally
and it also during low CO2 environments. How can we reconstruct how vegetation has
changed in the past? The first thing that you might say is why don't we just look at
pollen. The problem with working with pollen is that pollens are often not very
well preserved in sediments. Any kind of oxygen inhaling deposition environment the
pollen will disappear. So we have a much more elegant way to explore which actually
exploits the biochemical way in which the photosynthesis works using the C4 pathway.
This is a brief overview of carbon isotopes. These are the two stable
isotopes of carbon. Carbon 14 is the radioactive or unstable isotope of carbon.
Carbon 12. Most of our bodies are made up of that. 99% of carbon in our bodies is
carbon 12. This is the most common isotope of carbon. Then carbon 13 is only about
one in one hundred or about 1% of the carbon in the environment. What we do is
we measure the ratio of carbon 13 to carbon 12 using a mass spectrometer and
then express that ratio as a change relative to a standard using this
equation. This is the only equation I will show for the day but this notation that
we'll be talking about. What we see here is that the C3 verses C4 with plant
signatures the grasslands have a much more enriched or more positive C4 carbonized to
value than to c3 plants. C3 plant will be trees and everything else. C4 plants in
the tropics are going to be this savannah grasses. If we jump forward to really
heroic collaboration that existed with the Naomi Levin and Thure Cerling over the
past decade or so. They've measured carbon isotope values from soil carbonates. Which
are these little carbonated nodules that form in soils that record the
photosynthetic pathway the plants that are above them. So you go to a geological
outcrop, you collect this soil carbonates, and you measure their soil carbonate. That
tells you what the vegetation was at the time that that thing had formed. What you
can see is this transition from lower values to higher values. Meaning an
increase in the grasslands. This transition is almost about a 50% increase
in grass cover. You can see that the timing of that transition is sometime
around somewhere between three and two million years ago. Compare that to this
record of the sapropels where you get very rapid cycling between wet and
drier conditions. This a secular change. This is a very rapid back and forth kind
of like a pendulum change. The way that we can now explore past vegetation changes is
actually very beautiful forensic tool that was developed which allows us to look at
fossils but this are not megascopic fossils. These are not fossil skulls, they
are not fossil shells, they not fossil paleosol carbonate nodules. These
are actually fossil molecules. The molecules derived from ancient plants. All
higher plants have an epicuticular wax that is waxes on the outer surface of the
leaves. You see in a rubber plant that's nothing but wax on the outside. Those waxy
molecules are very robust. They last for a very long time. We can take a sediment, we
can basically crush it and then put it in something that looks for all the world
like an espresso maker but it has very nasty solvents inside of it. We
will extract this straw-colored liquid which is loaded with these plant wax
molecules. Loaded meaning one in a billion of the carbon molecules in here will be
plant waxes. So they're not really loaded but they are sort of loaded. When we look
at them we can actually measure with the chromatography what the compounds are and
when you see this interdigitation between low and high peaks that just shouts out
you. Looks like a hand and says I am from the plant. This class of molecules,
this class of compounds are all drawn out from photosynthesis. What we can do is we
can take each of these peaks and then instead of blowing that carbon out into
the atmosphere we then direct it into a mass spectrometer. We measure the carbon
ratio of those compounds, that's how we can figure out whether that fossil plant
that made those weak leaf waxes was a C3 or C4 plant. My student, Sara Feekins
is now a tenured professor at USC did this at an ocean drilling
program site here in the Gulf of Aden. A place that's very difficult to go to
today. This is the extent of savannah grasses there today. This is her record,
basically a snap shot record from the site. You can see it shows that same
trend. That same increase in values indicating the emergence of the
grasslands. If you compare her record to the Naomi Levens' record you see they
both have this transition. This both sort of circular transition towards greater
grasslands. What's impressive is that these green periods are the same green
periods of major events of human evolution. You can see that these
transitions towards an initial expansion in grasslands after about three million
years ago. Then really their establishment around two million years ago is coincident
with some changes that we're seeing in early human evolution. What for me was the
biggest the most exciting discovery in this relationship between climate change
and human evolution was what showed up in the proceedings in the national academy of
sciences about a year and a half ago by Terry Serling but also a number of
co-authors contributed to this study. These are the same records that I showed
earlier. This increase in indicators of grasses sometime after three million
reaching peak values around two million. So this is basically the same figures that
I showed earlier. What Terry and his colleagues did was to measure the carbon
isotopes of the tooth enamel in fossil skulls. So they took the teeth and they
analyzed the carbon isotopes of the teeth and you are what you eat. You see this
relationship you can see that when you look at early ancestral humans or
ancestral hominids you can see their basically tracking the environment. If the
environment changes your chemistry changes. Basically the hominids are just
tracking the environment and you say okay we're done all right its working. I mean
basically they're just following environment and you can also say people
couldn't care less about the environment because look they're just tracking the
environment watch what happens. The one group that doesn't do that is us. These
blue dots are carbonized isotopic analysis of early and late members of the genus
Homo. You can see that they are falling away from their other lineage parenthesis
which they share the landscape with. So Paranthropus, their diet was mainly
derived from savannah grasses. Early Homo had a more variable diet and they were
able basically to extract a flexible diet from an increasingly inflexible landscape.
So more to come soon. This is my post-doc Kevin Uno for those
of you who want to see some truly spectacular new results that I'm
happy to talk about that. But really Rick Potts and Andy Cohen have been leaders
because they've lead a drilling program up and down the Rift Valley collecting more
and more of these sediment archives. So what I'm showing you is just a teaser for
what they're about to do. Thank you very much Charlie. [Hublin] Today I would like to present you some thoughts about Neanderthal evolution
and to what extent climate might have influenced their evolution. Before I start
with climate and Neanderthals I wanted to show you this slide presenting on the left
side a Neanderthal and a modern human both of the same age. In front you have two
skulls of extinct apes, bonobo and a common chimpanzee. This is just to show
you how Neanderthals are different from us in terms of anatomy, in terms of phenotype
in general. Modern humans and Neanderthal ancestors diverged probably about half a
million years ago. When bonobos and common chimpanzees diverged much earlier probably
somewhere between two and one million years ago. One of the, I would say,
mysteries regarding Neanderthals is what kind of evolutionally process was driving
these very rapid divergence. The way we like to think on the Neanderthals, the way
they are presented in the literature is this way. Humans adapted to a glacial
environment peri Arctic environment and as a matter of fact if we have a look
on this very jerky climatic curve that you're going to see quite a number of
times today I imagine. You can see that for the last half a million years 95% of
the time the climate was colder than it is today in the area where Neanderthals lived
mainly western Eurasia. This being said the climate was not always glacial. The
glacial episodes were rather brief actually. The most extreme part of this
glacial episodes. If you have a look on this map that's the map showing you the
distribution of places where Neanderthals have been found you see that actually
they're not documented very high in latitude. There is the northern most
Neanderthal every found was found 52 degrees of northern latitude which is not
so high. Neanderthals lived also in places like Spain and southern Italy and the
[inaudible 00:21:47] that never witnessed really glacial episodes. So the question
is what in their environment first of all drove their distribution and also drove
their evolution. The distribution that you see now is probably I would say misleading
somehow because it's a palimpsest of the distribution of Neanderthals through a
very long period of time. In other words at a given point in the past they had
never had these extension. So it's sort of addition of many distribution and it's
very likely that they reach this eastern most extension in the southern Siberia in
the Italian. This also true for the new east, south western Asia only at some
point in the late evolution. Speaking about climate and influence of climate on
evolution we have quite a number of studies showing how climate can influence
the biology and morphology of modern humans. Probably one of the most, I would
say, spectacular feature that relates to climate in extinct humans is the body
shape in general. There are a number of studies showing that the proportions of
the limbs, the shapes of the trunk varies with climate. Basically people exposed to
very hot climate need to cool their bodies, they tend to be slimmer, to have
narrow trunks, and longer limbs. People exposed to very cold environments they
tend to be more skewed to have shorter limbs, and wider trunks. This kind of
study it's multivariate study taking into account many population schedules. How you
can basically rank populations from the tropics. On the right side you have people
from East and West Africa up to the higher attitudes in green you have European
population. If you take measurements of the body shape of Neanderthal and you plot
it in this kind of chart. This is the case of one Neanderthal well known called
La Chapelle-aux Saints. It falls beyond any modern European and even beyond modern
inuits. It's said to have hyper [inaudible 0:24:39] body proportion.
Interestingly if you plot on the same chart early modern humans who came into
Europe about 50,000 years ago to replace Neanderthals they plot very close to
population from modern Sudan. Which by the way it's certainly one of the best
arguments to make them come out of Africa besides genetical arguments. However we
should be very I would say conscious with these feature because climatic adaptation
is not just a biological adaptation in humans it's also a cultural adaptation and
a technical adaptation. In other words we suspect that even if Neanderthals were not
exposed to always very cold climates because of the limitation of their
technology the biological response might have been higher than what we have in
extinct humans. As a matter of fact if we look at the archaeological record we find
very few archaeological sites left by Neanderthals in truly periArctic
environments. It looks like during the coldest phrases of the glacial episodes
large portions of Europe have been abandoned by the Neanderthals. There are
other features that have been said to be related to climate Neanderthals especially
their very peculiar facial morphology. They have a very strong mesial facial
prognathism. There's very big nose projecting and on the side of the nasal
aperture inside the face you have volumes which are sinuses which are said to be
very developed in Neanderthals in general. In a sort of naive way people have thought
for a long time that the development of sinuses in Neanderthals was sort of
insulation against cold. This idea has been very criticized actually it's
completely abandoned today because we see more of these sinuses as a sort of filling
an empty space between other structures that are adapted to different functions.
It's more interesting to look at another aspect of the face which is the nose.
Actually if you look at extinct humans you will see that one of the most varying
parts of the face is the nose and the shape of the nasal aperture. One of these
skulls comes from Germany and the other one from Zaire in Africa. Immediately you
can see that the shape of the nasal aperture is very different in these two
individuals. There are quite a number of studies showing that actually in humans
the nose and especially the inner nose is adapted to the climate conditions in
different regions. Primarily what we have is a problem with cold and dry areas.
Individuals population that are exposed to cold and dry environments tend to have
nasal cavities that are higher and narrower in order to increase the
turbulence of the air that is inspired and to increase contact between the mucus of
tissues and this air to warm it and to moist it. The nasopharynx seems to be more
depending on moisture. The nasal cavity itself with cold. What about
Neanderthals? At the first look Neanderthals seems no to march very well
this prediction because they have these huge nasal aperture that is somehow
unexpected if they were exposed to cold environments. Actually the business of
aperture is especially broad in its upper part which is not what we find in modern
tropical population. But if we look inside the nasal aperture we see that there are a
number of structures that inflate the walls of the nasal aperture in order to
narrow this nasal aperture. Although the nasal aperture is very bold outside the
cavity inside is much narrower and match the prediction we can make of a cold
adapted population. Last but not least we have now a number of information coming
from paleogenetical studies. I'm sure they are much more to come in the
future but we know already that a couple features of Neanderthals that we can
relate to the climate, the environment. I would like at least to mention this gene
called MC1R which is a receptor involved in the reder and fair complexions. Very
likely at least on the Neanderthals on which this gene has been detected we deal
with population with light skin color and red hair. We have some adaptation to the
cold environment in Neanderthals but the question is are there other effects of the
climate on the evolution? I would like now to deal with something that I found
probably more important than that adaptation itself. One of the questions
about Neanderthal evolution is why do we have this divergence between an African
lineage leading to us and this Arasian plague about half a million years ago.
What happened at this moment? Why then why not before? It raises the question of when
exactly we have the first Neanderthals. The first Neanderthals we have in the
fossil record are about 400,000 years. They are from in England, there are from
Spain and this age a little bit about 400,000 has been some time in conflict
with the dates that were provided by genetists. Genetists using molecular clock
base on computations, using the assumed time of divergence of fossil groups came
to a much younger ages for the divergence for Neanderthals and modern humans. You
know something around 300,000 that was a bit problematic for paleontologists but
recently because it's now easy to sequence the complete genome of parents and
children we can compare this genome. It has been possible to find that maybe the
rate of mutation assumed by this molecular clock was not quite right. New estimates
came with rate of mutation much more reduced about half of what was initially
thought. This new rate of mutation is confirmed by the study of some fossil
material. This is a female of early modern human found in western Siberia for which
we have the complete genome. We have the Beijing it's 45,000 years old so it's easy
to compare the genome of these early modern human who [inaudible 00:32:47]
and to have a notion of the rate of mutation along this lineage and it
confirms this reduced rate of mutation that has been recently proposed. It means
that the coalescence time for Neanderthals and modern humans fits rather
well this emergence in the phenotype, in the morphology around 400,000 or 450,000.
What has been going on in this time period? We have a list of features proper
to the Neanderthal that we see emerging through time by a process of accretion
and it's basically a shift in frequency of this features that we see
more and more a long time. About 200,000 years ago in the Isotopic Stage 7 we have
basically reached the Neanderthal morphology completely. The story unfolds
between 450... I'm talking about morphology and let's say a little bit less
than 200,000. It goes at different speed depending on different anatomical [sp]
areas and we suspect one of the most mechanisms driving this evolution is not
adaptation, is not selection, it's something that genetists call drift and
this drift is mostly depending on demography. What is it about? It's simple
you have availability of a population in terms of genes and in terms of
morphological features. If you reduce the size of this population, if you reduce it
dramatically and then re-expand this population you're going to have again a
large population but with a reduced variability just by chance. Just because
only some of these features went through this bottleneck. We have something like
that with Neanderthals and along the Neanderthal lineage. I could go through
several features, cranial features, and facial features. I just pick up one
example which is what we call non-metrical dental features. These non-metrical dental
features have a frequency that increase along the Neanderthal lineage. We know
they are a part of the viability of Neanderthals of the middle places in
hominids before the Neanderthal emergence. This seems to be fixed a little bit my
chance in the Neanderthals and reach a very high frequency in later form. What
could drive this evolution? We think this jerky curve that you saw several
times already. In this period of time say around 800,000 to 400,000 become even more
jucky. We have 600,000 years ago for the first time the first major glacier episode
in western Eurasia. We think that this first major glacier episode resulted in
for the first time an isolation of western Eurasia and a dramatic reduction of
population living there. This is confirmed also now by paleogenetics using the high
resolution sequencing of Neanderthal and the use of a genome. It's possible to make
assumptions on the evolution of the population size through time of these guys
and we that contrary to what we have in the ancestral of modern humans. We have
around 500,000 to 600,000 dramatic reduction of the population size of this
group. The story unfolds this way. We have in the early places seen western Eurasian
hominids. We see a lot of the changes between southwest Asia, Africa, central
Asia, western Eurasia and with the Isotopic Stage 16 about 600,000 years we
have probably for the first time this separation time that matches the genetical
data. We have another major bottleneck with Isotopic Stage 12 and soon after this
is when we have for the first time Neanderthal features emerging in the
phenotype of European hominids. Let's say 200,000 years later after a number of
other bottlenecks we have basically fixed this Neanderthal morphology. To finish I
would just like to say one word about Neanderthal extinction and I hope I
convinced you that climate played a major role in the life of the Neanderthals. The
question is did the climate play a role in the fall of the Neanderthals? There are a
number of theories about that that Neanderthals got extinct naturally before
modern humans moved into Europe. What we think about the emergence of modern humans
into Europe is a scenario that is a bit more complicated today that it was a few
years ago. We think we have two major episodes of colonization of western
Eurasia. Once corresponding to what we call the initial [inaudible 00:38:32]
sometime around maybe 48,000 and the later one for western of Eurasia around 42,000
to 43,000. It has been argued that in this time period the climatic curve is
especially jucky and that would have driven the Neanderthals to extinction
before or facilitated the replacement by modern humans. I think when you look at
discoveries it's very difficult to see I would say more jerkiness in this
period than before. I think Neanderthals survived all sort of climatic changes
before modern humans arrived in western Eurasia. I think the main disaster
Neanderthals had to face was not a climatic disaster. It was us.
Thank you. - [Potts] Now there are many
fundamental problems in the study of human evolution
and an immense array of really intriguing questions. In part
because the evolutionally journey has involved an astonishing transformation.
One way of looking at this transformation is through a pairing of slides. I thought
I would start with the laziest ones first but also the most endangering in some
ways. One way but it poses, this pairing of slides I'm going to show you, poses a
question. How is it that our ancestry included in an imaginative way in this
reconstruction dilemmas and survival challenges such as this? Then in our own
species that we can present ourselves with a survival challenge like this. How is
that kind of transformation even possible? Ed' White's space walk, the first human to
take a walk in space, and how was it if in fact evolutionally process tethered our
species through change over time. Tethered our species to human possibilities,
mentality and society to a particular ancestral habitat and to particular
conditions of life. How could that transformation have taken place? Another
pairing of slides I think capture this can be expressed in this way. The oldest know
stone tool tradition. The old one dating to about 2.6 million years ago. The
question that's posed here is how is it that our evolutionally journey and
technology go from something like this to something like this? As you can read there
this is space debris that is encircling the earth. As I write there the entire
planet has become an archaeological site. So in many different ways there are
species that resides on a human altered planet. In seeking to understand
transformation such as this we run right up against the fundamental scientific
challenge of seeing ourselves as a phenomenon of nature. And I think that
sadly the folkways in which we see our species are often seized in science
Homo sapiens almost as an aberration of nature and dichotomies. The traditional
dichotomies line up in a series of false oppositions human verses nature, cultural
verses natural, learning verses instincts, and even human verses animal. It's
especially that later dichotomy that highlights the fausted division that
occurs in this particular perspective. Now human evolution is the period that we've
been looking at so far in these first several talks. Namely the past six or
seven million years of earth's history. Where the baseline adaptations and the
initial possibilities of our species emerged in ancestors who are no longer
around. One way to pursue the question of how the accumulation of adaptations
occurred over time is to examine the environmental context of that entire time
period. Data like this which has been shown in the previous two talks and also
was shown on the front of your programs is the oxygen isotope curve showing changes
in the trends and fluctuation in ocean temperature and global ice volume. It's an
iconic diagram of parallel climatology and it shows that the past six million years
corresponding with a period of human evolutionally history have been one of the
most dramatic periods of climate oscillation of the Cenozoic Era of the
past 65 million years. As Peter Dominica showed in his talk, "Parallel climate
records" express at least two signals the overall trend as well as the variability.
And up to about I would say 20 years ago nearly every student in the study of human
evolution considered the variability as simply noise in the all important trend
toward a cooler and drier earth. It was the direction of change, the onset of
grassland dominated Savannah in East Africa or Africa in general and of ice age
conditions in higher latitudes. That was thought to be the signal that elicited the
emergence of uniquely human adaptations. Yet all of the environmental records also
show periods of strong instability of amplitude variations as there were
switches between arid and moist and between cool and warm. Now among many
factors that have an influence on earth's climate system earth's orbital dynamics
certainly are one of them as expressed in this figure. We live on a spinning planet
whose access of rotation is tilted and therefore there are variations,
fluctuations in the amount of solar radiation that hits the earth at different
times of the year and at different places on earth. We see these three variables
represented here of eccentricity, the shape of the earth orbit around the sun,
the tilt of the earth axis also varies. Eccentricity the shape of the earth's
orbit the first factor goes from a more circular orbit to a more oval or
electrical orbit. The tilt of the earth's axis of rotation varies and also there is
this wobble in the earth's axis of rotation that relates to procession. When
you look at African climate and really climate all over the globe and African
climate is strongly influence by variation in solar insulation. Looking at two of
those variables it's the interaction of orbital procession which has cycles of
19,000 and 23,000 years approximately. Eccentricity, the shape of the earth's
orbit around the sun which has periods of about 100,000 years and about
413,000 years. You put those four wavy lines together, four basically sign curves
together and the interaction of them shows that there are this alternating phases of
high and low climate variability in tropical Africa. Peter Dominica has been
instrumental in helping me to understand this as we got together in a project a
number of years ago. So what we've been able to do and this is going to come out
in the publication soon is that we've been able to label according to very specific
intervals of changes between the high climate variability times and low climate
variability times of labeling back through time back over the last five million years
we've been able to do this. The highs and the lows. The times of strong instability
in East African climate where the aptitude of dry and wet were exacerbated, magnified
verses times of greater stability the low periods. What we've been able to show is
that the kinds of records that Peter has studied for example the dust records as
well as the wet dry cycles that are recorded in the Mediterranean are relating
to eastern and north east African climate support this alternation and this pattern
of division between high and low climate variability. The same paper that will come
out later this year also explores the places in East Africa where early humans
lived, where we find fossils and stone tools, do those also see fluctuations of
this sort. It turns out in that all of the really prolonged periods of high
climate variability we see also amplification in landscape variability in
East African sedimentary basins. For example this place with the almost
unpronounceable name of Olorgesailie in southern Kenya where I've been working for
the last 30 years we see that between 350,000 and 50,000 years ago which was the
prolonged high labeled H2 in the previous diagram. That time period that we see the
landscape changing in amazing ways down cutting of the basin and then the basin
filling up with sediments compared with earlier in time. We think that these are
under climate control, these vast changes in landscape. We see this for all of the
other prolonged high variability intervals. I wondered whether in these
prolonged high variability intervals what happened? Was there anything interesting
that happened in human evolutionary history? You can see the time scale of
five million years on the left and what I've recorded here are the eight that is
the 25% longest periods of high climate variability and the numbers we've assigned
them in the paper to come out. And we thought what goes on here? What can we
tell from the fossils and archaeological records? It turns out that almost
everything that's interesting in African human evolution is concentrated in those
periods of high climate variability. FAD it's a strange word but it just means
First Appearance Datum where a fossil or an archaeological piece of evidence show
us the beginning of a particular lineage in our evolutionary tree or behavior. So
for Australopithecus of all the major genre in our evolutionally tree
Australopithecus and Homo and Paranthropists are concentrated in a
period of predicted high climate variability also that of Homo sapiens at
the top of the chart there. And also the origin of every single major technological
and behavioral transition in human evolutionary history is focused in one of
these prolonged high climate variability intervals. Now one thing that could be
easily criticized about this is that yeah but new fossils are found all the time and
they're going to be new find that are made. That happened about a month and a
half ago with a fossil jaw from Ethiopia that re-positioned of the genus homo. It
turns out it re-positioned it in the next in the oldest period of high climate
variability. Now I'm not saying that this is proof but it's nice to see a robust
predictive model about relationship of African human evolutionary history and
these periods of high climate variability. We'll see what happens next with the new
discoveries. We've also seen in our evolutionary tree we used to have the
march of hominids going from ape like to human like and that gave a sense of
inevitability about the existence of our species on earth. That idea has been
completely discarded and we see we are part of a much more diverse evolutionary
tree. In the context of environmental dynamics as the conditions of live change
with shifts in landscape and in food, water and shelter it makes sense that new
behavioral possibilities, new adaptations, and ways of life were at premium if they
could allow a greater degree of adjustment in this time periods of very strong
variability in the environment. This also means, since we're the last bipeds
standing, that other ways of life prior means of existence could not be sustained
and they were lost. in the light of environmental dynamics we can also inspect
this overview of the adaptive history related to the origin eventually of Homo
sapiens. We can now see these adaptations as the evolution of behavioral flexibility
and a wider range the development of a wider range of adoptive options and being
able to switch strategies essentially adaptability in the face of an unstable
world. I don't have time to go through all of these points certainly but we can point
out a few of them. For example things like a simple stone flaking, carrying of food
and stones across the landscape associated with the genus homo or ways of being able
to buffer the changing menu of food distribution and food abundance over time
during a high variability interval. The most rapid rate of increase in brain size
relative to body size. The brain is one our organ of plasticity and that also
becomes more understandable not as something that evolved in a specific
narrow set of environmental and survival conditions but in relationship to changing
circumstances. Increased cultural diversity and technological innovation
that of course is a characteristic of our own species and as multiplied the behavior
options within our own species. We also see in this chart the foundations for
human altered planet. For example the changes in technology, control of fire and
building of shelters even things like moving of complex moving of
resources across the landscape. We can see in the archaeological record and I will
talk more about that in a moment. What we see is that we have become very good at
surviving by modifying our surroundings and that humans as a result have spread
worldwide. Thus we have global change, global transformation of landscapes and
the consumption of resources even founded in this early evolutionary history of
human beings. My research team has been working towards the top of this time
period about 300,000 years ago and very quickly. These are some of the things that
were appearing in that period going back to 280,000 years ago and remember that's a
time period in Africa of prolonged high climate variability. We see the beginning
of innovations. We see increasing innovations, wider social networks, trade,
the beginning of awareness of groups that are distant far away that you cannot see
and yet you're able to have a sense of values, of valuable rock like obsidian
rock that was traded over long distance, complex symbolic activity, complex
thinking and planning. I would say this overall as in an environmental context
that we examine now Africa a greater capacity to adjust to new environments.
I'm not going to show you any more than that other than to say that our research
team is about to extend some of these traits even further back in time prior to
300,000 years ago. So what we then come up with is that the new theme and story and
the new theme and hallmark of our evolutionary story is one of adaptability
and increasing adaptability to endure change in the environment, to thrive in
novel environments, to spread to new habitats, to respond in new ways to the
surroundings. These are characteristics of the genus homo and especially embodied in
us Homo sapiens. Final thoughts. The long term view of human evolutionary history,
the idea of the inevitability of our species has been discarded; it's been I
think increasingly replaced by an emphasis on adaptability. When human evolution is
framed within the study of our pariah [sp] environments. Finally adaptability
according to the definitions that I just gave and the demise of ways of life has
been two sides of the evolutionary process. I think the question ahead for us
is that this is evolutionally history but in the cultural history that is now
unfolding will that still be the case. Thank you very much.
