– [Presenter] This UCSD-TV program is presented by University of California Television. Like what you learn? Visit our website or follow us on Facebook and Twitter to keep up with the latest programs. We are the paradoxical ape, bipedal naked, large-brained, 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. – [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..