It is my great pleasure today to introduce Kevin Bourdon,
who is currently an Associate Professor in the Department of Human and
Revolutionary Biology at the Harvard University.
Kevin is a part of Ecologist that focuses on how climate is affecting mammalians
and humans.
He got his PhD at University of Utah and has been working as a research assistant
at Columbia University ever since.
And it is our pleasure today to have him speak about deer Paranthropos.
What type of food did you eat or WTF?
Welcome Kevin.
Thanks, Sir.
You can do that.
Today I'm going to talk about the relationship between diet and evolution,
particularly human evolution.
And I'm going to take a different tack, and I'm not going to focus on us.
A lot of the discussion of human evolution is about us, us, us.
And this is a talk about Parenthropus, an extinct homonym.
The last one lived about a million million 22 years ago.
And this is a letter.
This is a Valentine's Day.
It's a love letter to Parenthropus asking, dear parenthesis, WTF did you eat?
Where that stands for what types of food did you eat?
And I'll try to explain why understanding the diet of organisms,
especially extinct organisms, helps us understand their paleo biology,
their their, their ecology in the past.
And this, this letter here, it's called an aerogram.
This is a pretty young crowd it looks like for the most part.
And long ago in the late Holocene when I first started in graduate work in Kenya,
I would get these aerograms and it was a single sheet of paper,
blue on the outside, lined on the backside and you could write
letters home.
So dear mum and Dad, I'm in a tent in the middle of nowhere in
Kenya.
It's hot, I'm tired and I'm dusty, etcetera.
And then you fold the piece of paper up to single sheet of paper.
The paper becomes an envelope.
It's pre stamped and you can send it anywhere in the world cost like a dollar
or something like that.
So I found an old you can't find them really anymore because nobody does this.
But I wrote many home to my family.
And so this is one that I wrote to parenthesis and hopefully you'll we'll
dive into a little bit why understanding the diet helps us understand the
evolution and particularly how we got here.
OK.
And since it's Darwin Days and we're celebrating the 216th birthday of Charles
Darwin this week, I thought I'd start with just some notes,
not direct quotes, but just notes on his thoughts on the
role of diet and evolution.
So I'll let you read those for a moment.
And clearly Darwin thought about the role of resources, resource acquisition,
feeding habits, etcetera on survival, fitness and reproduction.
He he also got into the idea of seasonal availability of food, things like that.
And so really at the granular level about the role of resources in evolution, OK.
So as Sarah mentioned, thank you for the introduction, Sarah,
wherever you are.
And also Ryan, thank you for the invitation to speak.
Sorry, I should have started with that.
I'm a paleoecologist and so I try to understand past environments and both the
the vegetation and ecology, the hydroclimate or like rainfall,
and also the organisms that live in those environments and how those are all linked.
And that's sort of highlighted in this schematic here on the left or the right.
Sorry, my left.
And the principal question my research group asks is how did climate change
influence major shifts in terrestrial ecosystems and what were the evolutionary
consequences?
OK.
And we can break that down into a couple bigger questions.
The first being what caused the emergence of the world's tropical and subtropical
grasslands starting about 10 million years ago.
So grasslands are a new feature on Earth, relatively speaking,
and I won't dive too deeply into that today,
but it's related to us and the evolution of hominins, our group,
because we are a very grassy species.
If you think about what you had for breakfast this morning,
it is probably a grass derived product.
I'll tell you I had yogurt and granola.
So yogurt comes from cows that eat grass.
Granola is a grain, oats, which is a type of grass,
and I can drink coffee without Creamer, but I prefer it with Creamer,
which comes from grass.
So we have a really grassy diet.
You can think about your lunch, your dinner,
as long as you don't get hungry here.
But we are a really grassy based species and that will come through in the talk
today.
Although I won't talk about necessarily the evolution of grasslands,
I'm going to focus on this second question.
Did climate and vegetation play a significant role in the evolution of
humans and other large mammals?
And this schematic kind of shows the linkages between climate variables like
the amount of rain an ecosystem gets, what the CO2 levels are in the atmosphere.
Plants take in CO2 right to to produce, photosynthate and to grow.
And then temperature plays a huge role in what kind of plants can grow in an
ecosystem.
So these are climate variables in the left and the ecosystem,
we have things that control vegetation structure.
So tree mortality, OK, depends on things like fire or bibary.
And then we have this balancing act between grassy and woody ecosystems.
So you can think of a pure grassland like in the Serengeti or Woodlands or forest.
There's a huge range of of ecosystems in Africa where where the work that I
present comes from today.
OK.
So focusing on this second question, OK, did climate and vegetation play a
significant role and how we got here?
We have these this sort of patchy fossil record.
Maybe you've seen sort of phylogenies like this where we have some fossil and
then we think it gave rise to other species, things like that.
And what we're exploring is the link between climate.
So here's some, let's just call it climate data of maybe
where where these hominins are running around on the earth.
And then here we have a more global record of say temperature,
ice volume or something.
And how do we link different scales, So global records of climate or regional
records of vegetation with the fossil record that's a little bit patchy.
Well, first we need to generate these global
records, local records of, you know, vegetation, climate, etcetera.
And then we need to generate this record.
And this one we we know how to do and we've been doing it for a very long time.
OK.
And that is we, we just go to the fossil record, OK?
It's an amazing, amazing archive of the story of us.
And here is the Leakey family.
This is Mary Lewis and one of the sons.
It's probably Richard Leakey at Old of I Gorge,
probably in the early 1950s or so with one of their mini Dalmatian dogs that
they kept.
And here in Aldevye Gorge is where Mary discovered this particular homonym.
This is Parenthropus.
Boise Eye, originally called Zingianthropus,
but the genus name is eventually changed, or his name before, actually.
It's a complicated story.
Anyway, This is Parenthropus.
This is 05 old divide hominid 5.
It's a specimen number.
It's famous because it's a skull.
Often times you find a tiny tooth or something,
but occasionally you get lucky and find a skull.
So the hominid fossil record has been in the process of being assembled over the
last century or so, and it continues to grow.
This is my colleague Isaiah Nengo, who sadly passed away several years ago,
one of the the 1st Kenyan paleoanthropologist who studies human
evolution.
And in the Turkana Basin where Doctor Mana and I work,
Isaiah discovered in 2014 this baby ape skull.
You can hold it in the palm of your hand and it's 13.3 million years old.
It's absolutely incredible.
They did some synchrotron scanning of it and you can see the molars forming up in
the crypt still inside the jaw.
And it's provide a a beautiful window into the evolution of apes 13 million
years ago.
So the fossil record has produced some pretty amazing specimens that tell us how
we got here, but the fossil record is incomplete.
So I'm going to spend a little time on this diagram so that I hopefully can
convince you that even though the fossil record is beautiful and amazing,
it leaves something to be desired.
So let's take our hypothetical hominin in orange here, OK?
And it's species range through four different time slices.
Time 1234 going up the Y axis is outlined in orange.
So in time one it's here, time 2 it's widely spread,
times 3 it's just sort of to the North East and time 4 to the West.
That's the the real sort of range of this this particular Organism through time.
The circles ABCDEF are fossil localities.
OK.
If it's a white open circle, that means that no fossils are found
there at the particular site.
If it's green, that means at that time period there are
fossils.
So time one.
OK, our hypothetical hominin is around and
it's in the southern range here.
Are the ranges here OK, But because the circles are open,
we never find fossils of it.
It doesn't mean it never existed, it just means it wasn't recorded in the
fossil record.
OK.
In time 2, we see that our hypothetical hominin has
expanded its range to South and then up the Rift Valley into eastern Africa.
And we see it at these two sites and this site and at this site C that wasn't part
of it's home range, but there are fossils, OK.
So we end up having this real record in orange, OK.
A second challenge in addition to our incomplete fossil record is that we have
different scales of questions and evidence.
So on the left, this is the scales of our questions and
you can pick a question up there.
I'm going to talk about diet today.
And on the right we have scales of evidence.
OK, so you need to, the point of this plot is to say your
question should be answered by evidence at the appropriate scale.
And our axis are space.
It's a log based scale of square kilometres and time.
They're the same on both in years, log base scale years.
So something like a fossil site where you find a fossil, you know,
footprint or something or some fossils can answer really local questions,
small scale questions, but important.
What was the paleo environment of a particular hominin fossil occurrence?
OK.
And then you can scale up to longer time scales about, say,
macro evolution or biogeography.
But then your scales of evidence need to also expand.
So if you want to ask about biogeography, you should be looking at a base and scale
something like perhaps this or this.
OK, so this is a nice road map that my
colleague Tyler Faith published telling us all don't scale jump.
Don't ask a macro evolutionary question with, you know,
a data set that's not appropriate.
It's too small scale.
So you can check me on that and make sure I follow those rules today.
OK, I know all the biologists got out of
class this week, but you still get one very short class
today.
It's like 3 sides long.
It's called hominins, one O 1.
This is the fossil record of the hominin lineage.
It's the Hominini, our tribe in the group, or the family Hominidae,
which includes great apes and us, so Gorillaz, chimps, etcetera.
The earliest purported hominins stretch back to about 7,000,000 years.
It's Sahelanthropus chadensis from central Africa, from Chad,
Auroran tuganensis from central Kenya, and Artapithecus,
Cadaba and Ramidus from the Awash in Ethiopia.
OK, these are relatively small hominins, small brain, small body, short limbs,
probably bipedal.
We think most of them were bipedal, meaning walking on 2 legs,
but we're able to climb much better than we can, OK.
And then we have the australopithecenes here coming on the scene around 44.34.
2 million years ago.
And here, this one, afarensis, Australopithecus afarensis is Lucy.
Lucy's 50 years old this year, was discovered in 1974 at Haddar by Don
Johansson and colleagues.
And then this is where you get the split and and remember the how incomplete the
fossil record is, OK?
This is our our sort of the way most people lay it out.
And it's grouped into to grades, OK?
And so there's a grade that goes off to the right and a grade that goes off to
the left.
OK, And that happens to be Parenthropus and
us.
OK, We're way up here, right?
This is a parenthesis skull.
These two are parenthesis skulls in the most defining feature is the sagittal
Crest.
There you can see, right.
So if you saw like, you know, Homo erectus walking down the street,
you probably just walk by be like, OK, but if you saw one of these walking down
the street, it would be you would turn your head and
stop and stare because they're very different.
They were.
Well, I'll go, I'll show you the next couple of slides.
But morphologically they were very different than us.
You would not mistake them for us.
Whereas something like Homo erectus or **** regaster, you might OK,
see we're already in the next course hominids one O 2.
So plotted here, we have age from three million years ago
to present on the X axis and two Y axis.
This is probably the easiest one to look at.
This is brain size, endocranial volume in cubic centimeters.
So whoever just won that water bottle, can you hold it up?
OK, so that's one litre that's here.
It's not so far from the size of our brains today.
The the total volume 1.2 litres or so, 1200 CCS and here's parenthesis in
circles through time.
And here's the **** lineage through time in terms of brain size.
So you can see there's 22 relatively different trends.
OK, there's this is parenthesis increase in
brain size going from somewhere in 400 maybe to 5 or 600CC.
And then here's us starting at around 600 and and sky rocketing up essentially
doubling in size.
OK, so big brains win.
Obviously we're here.
They're not.
I'm kidding.
That's a simplified version.
And then on the right here we have the the body plans and again I mentioned
parenthesis is very different looking.
It has it's much shorter and it has this sort of flared rib cage, OK,
where ours is more narrower, it's different in the pelvises.
And then the limb bones are very different.
We have much longer legs, right.
Look at the femurs there.
OK.
It's important to note that the bones that have been found for parenthesis that
have been really connected to that species post cranial are very few.
They're shown in the sort of shaded sections there.
So and because **** and Parenthropus were around at the same time,
if you find an isolated bone, it's hard to say which which genus it
belongs to.
OK, so here's a quick summary of Parenthropus.
And I think if I do this.
OK, so here's the skull, here's the sagittal Crest.
OK, And as the the 3D rendering rotates, I want you to notice how flat and and
prognathic or slope the faces, OK compared to us where our face is very,
very flat, OK, It also has this huge zygomatic arch here,
right?
So there's some morphological differences that I'll explain why we think they were
there, but a very different skull compared to a
human skull.
OK, with the teeth, I'm going to now focus on the jaw.
The lower jaw here, it has an incredibly robust mandible.
The Bony structure here is very thick and tall and wide.
And then the most remarkable thing are the teeth, OK,
so that these huge flat teeth and even the premolars here have become molarised
or inflated so that you have this huge amount of chewing surface.
So everybody look at your thumb.
OK, so that's about the size of the occlusal
or chewing surface of a Pyranthropis molar.
OK, now look at your pinky.
Put it next to it like this.
And that's about the size of your average molar in a human.
So massive, massive teeth, thick enamel, very, very thick enamel.
And so the question is, why did they have these teeth?
It's been a question since the beginning.
So and Speaking of which, the beginning is in 1938.
Parenthesis robustus, so same genus but from South Africa was
discovered at Crom Dry Cave.
It's around 2.2 to 2.1 million years.
It's a pretty limited window and we don't actually know the phylogenetic
relationship.
They're in the same genus that people argue if they're if it's convergent
evolution, you know, the large teeth and the sagittal Crest of
the South African robustness versus the East African species,
which are athiopicus in Boise Eye.
So athiopicus is the first it was around about 2.62 point 3,000,000 years ago.
And then Boise Eye is the the younger variant,
which was around for almost a million years.
Pretty long run.
We've only been here 300,000 years humans.
So and this this is AOH 5 discovered by Mary Leakey at old of Eichorge.
So early diet estimates based on a tooth morphology structure.
First leaky suggested was carnivorous, hypercarnivorous.
Then later many thought it was a hard object feeder and it became known as
Nutcracker man.
OK, because seeds and nuts have really high
caloric density.
They're great food, but it wreaks havoc on your teeth.
If you've ever chipped tooth, you know what I'm talking about.
OK.
All right.
So where did parenthesis live?
Yeah, that's the root.
It's showing the root.
Yeah.
They just have really deep roots.
Ours have pretty deep roots.
Not that deep.
Yeah.
So it's very deeply rooted.
Everything's robust about these things.
They're called megadon.
So big teeth.
It's called the megadon clade or grade of hominid.
OK, so where did parenthesis live?
These are sites where we have found parenthesis fossils.
So here's.
Southern in Tanzania and southern Kenya, old Avai, Laitoli,
Peninch and then moving up into Kenya.
Interesting.
It's never been found in Ethiopia.
Highly, highly fossiliferous.
That's where you know, lots of Lucy like things have been found
and many, many early **** fossils.
Oldest ***** from up here, but it stretches all along the Rift
Valley, even down all the way to Malawi.
This is a key site found in the 90s that expanded the range.
Remember that earlier plot of where?
Where were these hominids living?
Way far South to the southern rift.
OK, so yeah, again, where did Paranthropus really live?
Maybe we don't know yet.
People are really confused why it's never been found here.
Was there a biogeographic barrier?
The environment not right?
We don't know.
Or did we just not found the fossils?
And then most recently, this last fall, a new Paranthropis site was discovered
here on the Houma Peninsula, Lake Victoria.
It extended the age back to 2. 8 million years.
So I have to update that previous slide and the range.
OK, so these things are always changing.
Yeah.
I was just wondering if you're not going to know what the the ranges of time are
for T1 through T4.
Oh, it's just hypothetical.
It's like an exercise in what what is what do we actually know and what really
happened?
Yeah, good question.
OK, So why should we be studying our interest
in the diets of these things or even us?
OK, well, animals interact most of their
environment when they're feeding.
So there's a lot of information about their ecology through their feeding
habits, how much time they spend, where they go, what they eat.
Is it a seasonal available resource?
Is it available year round?
And from that we can begin to ask, in the case of us,
and I showed this earlier, the encephalization of the massive
expansion of our brains, did diet lead to our big brains?
The answer is almost decidedly yes, because the brain is a really expensive
tissue or organ to run, and we need a lot of calories for that.
OK.
Also, diet informs us about what's available,
what's on the menu, Habitat resources gives us some idea for
niche breath.
So what this whatever Organism can eat or survive on and is it competing with other
things in that ecosystem.
It can inform us about how food drives selection of dental phenotypes,
thicker enamel versus thinner enamel, big teeth, small teeth.
And an important point is that fossil teeth provide a record of diet in in many
different ways.
OK, so here's here's some examples of how we
can study diet.
And the important thing is that the morphology of the shape,
what these early studies were looking at are recording sort of macro evolutionary
processes.
So those are out here and we've got on the Y axis time here.
So studies of like collecting dung and things tell us kind of about the last
meal or the last few meals, two things modern ecologists do.
Or you can look at stomach contents or field observations.
Those operate over the time scale for like, you know,
a day to a year or something like that.
And in the fossil record, we use a variety of different techniques.
I'll talk about microwave briefly and stable isotopes.
And those span years, centuries of Millennium because we have
the advantage of looking into deep time.
OK.
So the morphology tells us what the Organism was able to eat,
what it long term evolved to eat.
But these things like micro wear, which is the scratches on the surface of
the teeth and isotopes give us week to season to annual scale time windows.
So it's what it indeed it what it was really eating,
not what it was designed to eat.
And those don't always match up.
OK, All right.
So micro wear tells us about pits and scratches on a tooth and if you're
crushing like a hard object versus shearing.
If you watch a horse or a cow eat, they do a lot of shearing, right?
It's sort of like this with the teeth.
OK.
And so they, we've done this microwave analysis,
we the community, not me.
And we look at something called complexity, which tells us,
are they accessing softer or harder foods?
And in the case of Parenthropus, here's the South Africa and robustness,
and here's the East Africa and Boise Eye, they have pretty low complexity
suggesting softer foods.
This was a big surprise and was the first nail in the coffin for The Nutcracker Man
hypothesis.
And now I'm going to move into stable isotope methods.
And this is the one slide where you just need to pay attention for a quick second
because most of the talk is based on this principle here, OK?
Carbon isotopes are stable isotopes that exist in nature.
We are all about 1% carbon 13.
It's not radioactive.
And the rest of us, carbon 12, tiny bit of tiny,
tiny bit of carbon 14 in US, OK in Africa today and over the past 10
million years, trees and shrubs which produce foods like
leaves, seeds, fruits and nuts use the C3 photosynthetic
pathway and that has a very distinct carbon isotope ratio.
And all grasses, all, pretty much all lowland grasses in
Eastern Africa are C4 grasses and they have a very distinct carbon isotope
signature and that also includes some sedges and then their underground storage
organs like tubers or corns.
OK.
So using carbon isotopes, we can tell something is browsing or
using eating fruits and nuts from from C3 plants or grasses.
There are obviously seeds of grasses, right?
We eat them all the time, but we can differentiate between these
two food types using isotopes, and these isotopes are stored in our
teeth as your teeth form through your childhood and into your adulthood,
when you finish forming your wisdom teeth, so we can go back.
This is a broken fossil tooth of Australopithecus from Ethiopia.
Here's the enamel.
This dark part, when it fossilizes, it turns dark.
And we just drill here, remove some powder, put it in a vial,
take it home, measure the carbon isotope ratio,
and voila, we have the diet of that particular
hominin from this is 3. 4 million years ago or something like
that.
OK, Carbon tells us about the diet, the proportion of C3 brows to graze that
was in it, and oxygen tells us about it.
Body water, it's environment.
OK, so you are what you eat and drink.
OK, so now we're going to dive into some data
from northern Kenya, southern Ethiopia.
This is the Turkana Basin where the Leaky family worked for many, many decades.
They're still active, in fact, Louise Leaky.
And there are three main geological formations here,
the Shingura and Nachikui Niku before, and they're all pretty much the same age.
They just have different names because they're far apart from each other.
But at some point, some geologists realized, hey,
wait a minute, these are all the same.
They're tied together.
We still call them by different names, but they they all represent the same time
period of about four to 1,000,000 years, key time in human evolution.
And so they were all tied together by volcanic ash layers.
So here's the Shingura Formation in the north,
the Nachikui in the West could be for in the east.
And this is the thickness of the outcrops of the stratigraphic unit compiled.
So in the Omo up here, there's about 700, almost a kilometre thick of sediments.
And we can date the ashes in the Rift Valley.
These volcanoes are erupting all the time.
You can see 3.43 point.
I can't read that zero or something 1,000, 000 years.
But we have a amazing, amazing age control because of the
volcanic activity of the Rift Valley to precisely date these fossils.
So we know how old they are very precisely.
And we can also tie those volcanic ash layers because they have chemical
fingerprints that are unique.
So if we find it here, we can look for it here and fingerprint
it.
And in that way, these lines tie exact time horizons
together.
And in this way, we can integrate the entire fossil record
of this whole basin and ask questions about human evolution.
So it's the richest hominin record in all of eastern Africa.
It's the best dated and people have begun to notice regional differences whether
you're living along a major axial river on the shoreline of a paleo lake.
It's just a wonderful sort of test bed for evolutionary theory and and study.
OK, so about a decade ago we published the
first data set of hominin diet and it came from these two formations around the
lake.
And here we have age from 4 to 4,000, 000 years to present.
And here we have the the carbon isotope value.
But I just put the tree in the grass here so you know if it's the C3 diet or AC4
diet.
So leaves, seeds, nuts, etcetera and grassy.
OK.
And then these are the various hominin taxa we analyze starting with
Australopithecus, anemensis, Kenyanthropus.
And then throughout the talk, all the purple dots are Parenthropus and
the anything in blue is some blue diamonds or some variety of of the genus
****.
So the important takeaways early on this particular taxon was just eating C3 foods.
And then when we moved to Kenyanthropus, suddenly there's a huge increase in the
breadth of their diet, including C3, but also mixed feeding,
combining C3 and C4 foods.
So we know that's an an expansion of the dietary niche.
OK, Then the record in this part of the basin
is pretty silent between about, I don't know, 2.8 and 2.2.
There's a few fossils, but there's not a lot.
So there's this huge gap.
There's a gap here and obviously a huge gap here.
But this is where something interesting happens.
We go from the Australopithecines to these two new genera,
Pyranthropus and ****.
And you can see from the plot there's a huge amount of dietary difference between
Parenthropus up here and **** down here.
There's very little overlap.
So it's almost like they said, OK, they're at the grocery store and like,
you can have that aisle.
I'm going to have this aisle, right?
There's niche separation.
OK, So that was 10 years ago and it was the
first comprehensive data set we had of hominid diet through time using this
isotopic method.
In 2020, this group, John Wynne ET Alt looked at the hominin
fossils in Ethiopia, same age, but they really keyed in on this
phosiliferous region from about 2.7 to 2. 2.
So it sort of fills this gap and the numbers are more or less the same.
Sorry, the writing's a little small, but purple's parenthopis and blue is ****
and it suddenly the story is a little bit more complicated, right?
You see blue and and purple overlapping, which you don't really see here.
OK, so it, this is just so easy story is now
suddenly like complicated, right?
Furthermore, they did some change point analysis and
found that in general there, there are some early paranthopenes down
here and **** and then at 2. 4 million years,
they all slid up this dietary scale and began incorporating much more C4 in their
diet.
So the question is why is there an environmental driver to that?
OK, so we have these two data sets.
Of course we have to add a third data set.
So in 2019, I went to the the National Museum in
Ethiopia with my colleagues and it's our taxi driver every day.
And these are all the hominin fossils, these isolated teeth,
they don't let you like drill or sample teeth that are in these beautiful skulls.
We, we work on isolated, generally broken teeth.
Then we can identify the species but are not morphologically as valuable.
OK.
And from that previous slide on the methods,
we mostly sample broken teeth because we can see the enamel dent injunction.
It's just really the right thing for everybody.
Anyway, all these little, they're like film canisters,
if anybody knows what a film can is with the specimens in them.
And so we go and I put on this little visor that magnifies things and you take
a Dremel little tiny dental bit and you drill some powder.
So we went and drilled, I don't know, about 80 or 90 teeth of hominids,
but also lots of primates, baboons, circle pittacoids, all these things.
Importantly, we're also adding something called
calcium isotopes, which tells us about perhaps trophic
level, something that this carbon isotope method
doesn't tell us about.
And so our goal was to contextualise hominidata with herbivore and carnivore
isotope data.
So what everyone else was eating on the landscape, add new data.
And then at the end I'm going to talk about actually trying to characterise the
ecosystem itself.
OK, so here's our data from this region, the Omo and again we see that
Australopithecus had mostly C3 diet, but varied maybe contracts through time.
The pink shrinks into a narrow vertical range.
And again we have this C3 sort of diet for **** paranthus down here and then
shifts up here and there's they're all mixed up still.
OK, so if we we overlay oh, and we see as the previous group did the
same 2.4 million year dietary shift, blah, blah, blah, yes, OK,
so now I'm putting all three studies together.
It's a messy plot, right?
The key points are that in the Pliocene, which is this geological window here, OK,
we see the dietary breath increase and that's shifting from this particular
taxon, Australopithecus and emensis to a new
genus, Kineanthropus, Platyat and Australopitheous and they
have a much.
So this huge opening up of hominin diets, that's a key.
So a key question is what led to this massive expansion ecological dietary
niche breath.
We see contraction of the osteopath diet.
So it goes from really broad, these dark pink squares to really narrow.
We see this shift in the Omo and then eventually we see this niche partitioning
between paranthropist and **** and they they take their own aisles of the,
the grocery store.
OK, so we have to go back to our handy guide
of are we asking the right questions at the right scale?
And I would say, yes, we're trying to understand ecosystem
change and diet.
And we're looking at outcrop based records,
fossil records being collected over, you know,
the fossils we analyse were collected essentially over the last century.
So we're working off the efforts of many, many people over many, many years.
OK.
And this particular place in southern Ethiopia, the Elmo Valley,
has some fossil sites.
So fossil collection area might be half the size of this room, OK.
So really, really localized.
And in some of these small areas, we find many, many hominins,
relatively speaking.
So we can actually get to a very granular scale.
So here I'm plotting the carbon isotope ratio here.
So this is diet C3 versus C4, and this is oxygen.
Remember, this tells us something about their
drinking water, leaf water, their sort of body water signal.
And again, purple and blue represent the two general
we're interested in.
And you can see that in carbon space, they're pretty close,
and they're almost identical in the oxygen space.
So pretty similar diets here at a single site.
So this is like a single slice of time.
It doesn't mean these fossils were or these hominids were living at the exact
same time.
The geologic record mixes time up.
But let's say this is something like a 10, 000 year time slice,
which is really good resolution when you are 2.3 million years back in time.
OK.
So we can see that there was strong dietary overlap.
And that question still remains as to was there an environmental pressure or change
in the vegetation or resources available that pushed all the hominids into
essentially the same dietary niche?
OK, So to answer that, we decided to actually look at the
vegetation.
What was the vegetation like?
So we have to get out of the teeth and into the ecosystem to understand what the
plants were doing.
OK, So we went to the Omo, the place where all these fossils are
from.
And these are now biomarkers, which are molecular plant fossils.
And plants die.
They leave some waxes in the sediment, just like if you have a jade plant at
home, you know, they're really waxy.
Those waxes actually record whether that plant is AC-3 or AC4 plant.
So we go and we get these waxes out of ancient sediments from 4 to 1,000,
000 years.
And just as we did with the teeth, we can actually reconstruct the amount of
woody to grassy vegetation on the landscape.
And so each dot is a measurement from the fossil soil where we take the waxes and
say up here at this particular point the landscape was about 30% C 4 and 70% C 3
vegetation.
So the overall trend you can see is moving towards more C4 on the landscape.
These are just histograms where we're bending.
It sort of highlights that shift to the right.
OK, we looked at mammal diet.
So you know, elephants, pigs, hippos, rhinos,
everything running around and they using change point analysis,
we see there's a shift here at about 2. 7 million years, OK, to more C4 foods.
And then here's the sort of hominin lineage structure at this particular
fossil site in the Omo.
You have Australopithecus for a while, then you start to see the Parenthropus
species come in, and then **** comes in around 2.
32 point four.
OK, we'll set some pretty old stone tools
here.
OK, Now we have some enamel data from the
teeth of the hominins, and we can see that compared to other
herbivores, OK, Or let's say mammals.
We don't know if these were herbivores or not yet.
The dietary shift comes a little bit later and that's pretty common.
Not everybody's going to change at the same time.
Different organisms have different ecologies, OK.
So this shift I think can be explained by this shift in in available resources.
We went from having more C3 type woody vegetation on the landscape to more open
resources on the landscape grasses and things or tubers of those grasses, OK.
So to me, that's the best explanation for why
perhaps the hominins all got packed into this small dietary niche space over here
and then later differentiated again.
OK, so here's some key key takeaways.
We see this vegetation shift AT27 and consequently following that different
mammal groups change their diet at different times,
with hominins all moving up into this more C4 or grassy base diet around 2.4.
Where on the flip side, some of the herbivores responded right
away, even earlier to that, OK, so perhaps had more dietary flexibility.
So why, why did the hominid diet lag other
mammals?
Is it interspecific competition?
Is it environmental pressure?
We don't, we don't know.
It's a really difficult question to answer.
But by collecting more and more data, we start to get at these questions or be
able to answer them.
OK.
And importantly, the spatial and temporal scales of the
vegetation proxy and the diet proxy are similar.
So we're following the rules here.
OK, so long-awaited.
Here's my love letter and my conclusions to parenthesis.
Dear parenthesis, we now know, thanks to isotopes,
that through most of your time in Eastern Africa,
your diet was based on 65 to 80% C four resources.
You surprised us eating C3 foods and mixed C3 feeding in the Omo.
There's a few two data points that were surprising us,
but we know you did this in Malawi too.
In the southern southern African sites.
Microware shows you weren't eating hard food.
I'd hard food items, low complexity.
That's a microware term, but instead tough items.
So it was doing more shearing like this, right?
Some of the grass eating mammals.
So did you eat meat?
I bet not, or not much.
We are going to measure calcium isotopes in your teeth with colleagues Jeremy
Martin, Vincent Balter, Pierre Jean Daudin in Lyon to try to find
this out.
It's a hard measurement to make.
So our French colleagues are doing that.
And my colleague Gilles did the microware.
So we're trying to do some niche breath modelling.
Sorry, I'll keep reading using microware isotope
data.
We hope you don't mind.
We won't call you a Nutcracker A Nutcracker anymore,
but your diet and ecology is still a tough nut to crack.
Yours truly, Kevin, on behalf of my many colleagues.
And then PS what happened in the Omo from 2.7 to 2.3.
Dying to note, which is outstanding.
We can't can't quite figure out.
OK.
And then I thought I'd just close with in the Earth and evolutionary and paleo
science is some of the efforts under way at Harvard and and in the larger Earth
science community to increase diversity, equity, inclusion and anti racism.
So it's just some examples at Harvard.
The main thing is to listen, learn and discuss.
Professors are really good at talking.
We like to talk a lot.
So this is a challenge for me listening and this these are some of the
initiatives we're trying to put forth to increase diversity sciences.
We participate in this thing called URGE Unlearning Racism in the Geosciences.
That's a nationwide effort.
And so one of the things we've been doing is, is training African sciences,
African scientists.
There's a master's program that is operating in the Turkana Basin.
It's the only masters in the entire country of Kenya focused on human
evolutionary biology, despite them having probably the best
record of human evolution in the world.
And this was started by my late colleague Isaiah Nengo in 2018.
And there have been about 9 or 10 graduates.
It's a very small cohort, like 3A year, but I think out of the 9 or 10 graduates,
like 8 of them are now in PhD programs in the United States or Europe.
And they really need this sort of bridging masters program because the
undergraduate education is lacking in paleanthropology,
biology and things like that.
And so it's really a way to help them get prepared to enter PhD programs in Europe
or the US And so we do things like train them on how to drill teeth in the museum.
This is doing some water isotope extraction at our lab in Kenya is
building a rainfall collector so we can measure water isotopes of rain.
And then a lot of work in the National Museum of Kenya,
which hosts perhaps the most wonderful fossil collection in the world for
understanding human evolution capacity building.
That's another big effort is to actually build labs and infrastructure in Eastern
Africa so that researchers and students can have access to these facilities and
and be trained in Kenya rather than having to go abroad.
So we established this what's called the Permil lab,
Paleoon Eco hydrology research, Impala isotope lab.
This is the Impala research centre.
It's an ecology based research centre in central Kenya.
And so we have this laser water isotope analyzer and we go out and we collect
soil, we can extract the moisture from the soil.
We can get water out of plants and get it out of rivers, out of reservoirs.
And then here we are training students in the lab.
This is the lab manager, John Gitonga.
So capacity building is a big thing.
And then teaching.
So I, before I came to Harvard, I was at Columbia and we taught an
undergrad course abroad.
And they would just, the students would be there for a
semester.
I would swoop in for three weeks.
And we do all kinds of ecological studies using water isotopes.
This is again, extracting water from plants or soils.
We're not logging here.
This is a tree that fell next to a river in a storm.
The the stream eroded away the bank and the tree fell.
So we cut a slab out to try to do some tree ring,
like dendro ecology stuff using what we had.
We study what happens to bones on the landscape, like how to make a fossil,
things like that.
And then of course, we we hang out with the local kids a lot.
They're always interested in what the researchers are doing OK with that.
I thank you for your time.
I'd be happy to take questions after the attendance check in.
So good question.
So, you know, the the morphological characteristics
again, are this sort of macro evolutionary,
like what it was sort of evolved to do and handle.
That doesn't necessarily mean it's what it's actually eating at the time.
And so yes, pyranthropus had much thicker enamel and
that gave it, I think ironically gives it more niche
breath or possibility to eat more things than **** because we don't have the teeth
for doing that.
But it had the most restricted diet of all the hominins we've ever looked at
using this technique.
But I'll give you an example using elephants, right?
Elephants have these massively high crowned teeth,
and most high crown teeth in the mammal world are evolved for grazing eating
grasses because teeth wear down when you're eating grasses,
they're gritty and they're just much more abrasive than leaves.
So elements have evolved these really high crown teeth,
and we know they were eating grasses in the past using this same technique.
But today, Loxedana, the African elephant, both the forest and the Savannah elephant
mostly eat brows, They mostly eat trees.
So here's a tooth that's evolved.
It's specialized to eat grass.
It used to, but now it's using it for something else
and it's working fine.
The only reason elephants are in trouble is US, right?
Land use change, poaching, things like that.
So teeth can be evolved for one thing, but actually do other things.
And so it's probably more to do with the resources available on the landscape as
to why these two hominin genera were collapsed into a particular food type.
Yeah.
And I will say the isotope method is a little bit broad.
We just know it was C4 based.
It could have been a wildebeest that was eating only C4 grasses and then we,
our ancestors were eating that meat.
We can't tell between omnivore, carnivore, We can't differentiate that with trophic
level stuff with this particular method.
Yeah, I was just curious, do you keep any of the fossils for
yourself or you just give them to?
These are the national treasures of these countries.
And so I would be in jail if I kept them for myself.
And I'll just tell a quick student vignette, which is one year.
We're at a stone tool site with the students from Columbia and Princeton.
And one student who shall never be named, slipped a stone tool in their pocket and
they came back here and a year and a half later wrote me and said, Kevin,
I can't sleep at night.
I've done this thing, what should I do?
And so I called my stone tool friend.
Like we got a situation and he basically said you should just take it back with
you and put it back near.
But it's out of context.
So what I decided to do is throw it in the lake,
at this lake in the Lake Turkana, where it'll probably hopefully never be
found.
I don't know.
So this person is so guilt ridden that that they eventually gave that back.
So we always work under a very strict set of rules and guidelines to how we treat
the fossils.
Before we drill a fossil, we have to ask and get permission from
the museum research staff that yes, this one can be drilled because it it
damages the fossil a little bit.
But you get good information.
Thank you, that was a great talk.
I'm wondering about the ISO ratio itself ties to the food and they eat,
but what I'm wondering throughout that time zone,
the organs in itself is evolving and I'm wondering if the fractionation due to the
organs in itself, can we actually tell something about it?
Earlier species versus later species?
There's, you know, carbon or oxygen differences.
It's not due to the fact that the environment is basically organs.
How picking up 1413.
Yeah, or oxygen.
It's a really great question.
So he's asking like a 300 level, 400 level course question here,
which is when you eat something, the carbon gets incorporated in your
teeth, the isotopes.
But there's a a shift called a fractionation factor between the diet and
the actual mineral tooth that forms.
But we've measured that fractionation that offset across mammals.
And the biggest determinant is gut Physiology.
So unless we've become ruminants or we're ruminants and are not now that's the
biggest difference.
It's pretty constant.
It's about the same across primates.
There's, there's subtle variations on the order of
one to two per mil, but not over the course of like 3 to 6 to
8 per mil that we're seeing.
Yeah, good question.
The genes that do tooth morphology are famously so.
The shovel shaped molars from the Bering strain were actually modified for vitamin
D production in breast tissue and the change in shape of teeth was secondary.
Have you looked at EDAR gene or any of the genes that are involved in producing
teeth for biology?
If I knew anything about genes, I might.
I I'm in, I'm now in a biology department.
I'm trained as an earth scientist.
Yeah, and we're hiring a human geneticist and I
in, I feel like I'm in genetics one O 1 so we
can look at the modern genes in, in, in primates.
And my colleague Leslie Lusko, who took this photo,
is actually looking at genes in primates to try to understand the phenotypic
variation in which genes turn off which aspects of molar morphology.
She's in in Spain at an institute there.
But I have not.
And for like ancient DNA, we can't, we can't get that far back into millions
of years.
We can go back, say, 50 or 60,000 years.
But Africa has proved remarkably challenging for ancient DNA because of
the heat.
So the only ancient genomes that have been published from there come from high
up in the mountains where it's cooler.
All the sort of low insights that proteins at the end, everything's baked.
Yeah.
So great suggestion, way out of my field of expertise.
Yeah, I think they're really interesting though.
I think even if you could do A at a phonogenetic level,
I will say we have just recovered some ancient proteins out of tooth enamel
going back to 29,000,000 years and that, you know, these are small proteins,
but like enamel proteins, dentin proteins.
So they are preserved, but they're smaller snippets.
And I don't know that it's, it's not the gene, it's just a protein,
but it's a step forward.
Yeah.
Hi.
I just want to ask, let me just start with saying back to you,
let me mention how was your research done in Africa?
Because there's a bunch of evidence out here with that.
Would you say that'd be a more further support to the out of Africa.
Yeah, that's a pretty that has not been
challenged in any major way, at least for the early hominins.
The waves of out of Africa, there was an early Homo erectus 1.
7 million years and then later Homo sapiens left.
And so there's still a lot of debate about the timing and the nature.
Was it a push or a pull and what were the conditions like?
But yeah, it's not really the question as to where
hominins evolved at this point.
It's just how they left and when.
Yeah.
Any other questions?
So the bones are around you.
All right.
Thank you.
So you showed a figure with two skeleton so and **** and said that the leg bones
were much smaller and parenthesis, is that right?
They have like shorter, shorter, shorter legs, but pretty much longer arms,
I think, or proportionately shaded areas of the of
the bones were the only bones that have been actually found.
Yeah.
How do they know that their lives are short?
Yeah.
This is like a major reconstruction effort.
You're talking about this diagram.
Yeah.
Yes.
So you can tell a lot.
So here they have, I guess, 2 femoral heads and you probably.
I'm not a morphologist.
Not a paleontologist than a wannabe.
So this is fully reconstructed the tib fib.
There's some Ankley bone here, you know, whoop to do,
but here they're probably using the the morphology of the femoral head and maybe
the the thickness of the cortical bone.
I'm not sure I I tend to trust most paleontologists on this stuff.
The way they talk about bones is, you know, they're not,
they're not making this stuff up.
But it's true, we could use a lot.
We could use a lot more of this skeleton.
This is actually us.
This is just a **** sapien, your average human.
So it just really drives from the point of how incomplete the fossil record is.
Yeah.
Hand bones would be great.
Is there a thumb there?
Can't tell.
So if I got this correct, it sounds like for a period everybody
just kind of more converging on AC4 then.
But then after once we got past 2. 2 million years ago,
then **** genius like did we go back to more C3?
And are we still, I mean we still have grasses, right.
But was that because we started eating more foods from trees or even though the
landscape is still creating Savannah like yeah, I mean our great innovation.
I think what most people would argue is that where's the whoa?
It doesn't shine on there.
Whoa is so we're we're not fully see through.
You can see here we're kind of mixed.
And what I think the most popular evolutionary theory now is we ****
figured out a way to have these very generalist diets.
And that's been interpreted as flexibility.
And perhaps the reason why **** became a very successful lineage and parenthropist
who was kind of packed in at the upper end of that dietary range eventually went
extinct.
But we still don't know.
But the way people like to tell a story is in this ever increasingly harsh
environment in eastern Africa, as it became more arid, more grassy,
more resource limited or at least drier, we found a way to expand our niche breath.
And then you add like carnivore and hunting and stone tools and,
and that really changes the game.
But we think that Parenthropist may have been using stone tools as well.
Again, these are some of the great and many
unanswered questions.
Any other questions about you?
Actually, I have one and it's been totally outside
of your field of expertise.
The maps you're showing us are the incomplete fossil record that you remind
us about.
Has anyone sort of made an estimate 2. 2 million years ago how many of these
organisms were alive?
Well, the probably the best way to do that is
just to look in A at a fossil site.
The the record.
OK, how many fossils do we have here?
What are they?
And the general rule is that most sites, hominins make up less than 1% of what we
find.
So there is this conundrum of how these lineages survive both of them for a
million years or more for us millions of years 2.
6 and existed at such low numbers throughout the record.
And you know, now population, we have a different problem population,
but they were low.
We know that that they were low, but I don't know if there's been a number
of people talk about thousands and with ancient DNA you can look at relatedness
and like where this thing runs of homozygosity,
who's who's marrying who and breeding.
So in the more near term, we have records of that,
but that far back it's it's much more unconstrained, the estimates.
So payback on that.
What are the characteristics of the death of a person or individual that are
causing the impossible?
Is there?
Oh, just get buried, get buried fast and not in a box.
So that could that be river?
Yeah.
I'm wondering about lifestyles where they live.
Oh, there's there's a huge bias in the fossil
record.
And that's what we do, the students, we say, OK, let's look at this fossil,
what's happened to it, Have carnivores come and not on it, blah,
blah, blah.
And then is this going to be a fossil?
And if it's in the Highlands, the uplands, there's no way it's going to get buried.
And the sun usually just blasts away the the sun, the wind, the rain, soil acidity.
So the key is that often times there's a site that Sarah and I work at where every
other step you're smashing a hippo or croc.
And it's a hippo or croc because these are ancient river deposits.
And so naturally, the things that actually live there are
the ones that are most often fossilized.
So there's a bias in the record for things that were using river environments,
lake environments where you have burial, sedimentation process is happening.
Yeah.
Thank you very much.
Thank you.