CARTA: The Role of Hunting in Anthropogeny: Briana Pobiner – The Ecology of Hominin Scavenging
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CARTA: The Role of Hunting in Anthropogeny: Briana Pobiner – The Ecology of Hominin Scavenging

November 19, 2019


(beeping) (lively piano music) – [Narrator] 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. (ambient music) (uptempo music) – I’m gonna present some
data from a study I did to evaluate the ecology
of hominin scavenging but I’ll start by talking
a bit more broadly about how archaeologists can use evidence from butchered animal bones to understand prehistoric meat-eating in terms of potentially
both hunting and scavenging. So, if someone who studies prehistory I start with a totally blank canvas when I attempt to reconstruct
the diets of ancient humans. I try to paint a picture
of the past that I know will always be incomplete. We will never have all the pixels but I’m dedicated to finding the filters on the lenses through which
we can peer back in time and try to reconstruct
something rich in detail like this National Geographic illustration of what I can only describe
as a hominin meat picnic. (audience laughing) One of the fun things about
studying hominin meat-eating is there are so many
different lines of evidence that we can use to do so. We can use chimpanzee
and human forager diets and the talks earlier today
have addressed some of these. We can look at hominin fossils themselves, we can look at the size
and shape of teeth. The talk before mine by
Margaret addressed this a bit. We can look at jaws and skulls and we can look at even
body size and shape. We can also look at the chemistry which is what the talk
before mine really focused on of those actual hominin fossils. We can look at animal fossils particularly those with
direct evidence for butchery and that’s what I’ll focus
on a little bit after this. To do that we often use
a method called actualism where we either do experiments
or make observations in the present. We look at bones on the present for traces left of behavior from those
experiments or observations. We then look at fossils in the past, see if we can find similar traces and then we can infer
that similar behaviors occurred in the past. We can also look at the
archeological record at tools made by hominins that were used for meat-eating and we can even use newer methods like looking at ancient molecules. And so less than a year half ago a team of archeologists
announced that they found ancient animal proteins, basically the residue of blood,
skin and flesh from animals on the edges of 17 stone tools from an excavation in Jordan dating back to 250,000 years ago. It kind of blows my mind a bit that now we have direct evidence for even what kinds of animals
hominins were butchering a quarter of a million years ago. In this case we’re talking about camels, wild cattle, rhino, horses and duck. So I use a method called taphonomy, this is the lens that I
most often look through to examine the diets of early humans. Taphonomy is the study of
what happens to an organism after its death until its
discovery as a fossil. Here’s a great illustration by a paper by Nina Jablonski and
colleagues of a possible taphonomic scenario
resulting in the accumulation of giant panda bones in a cave in China. I’m particularly
interested in what happens right at and after death. So that’s that middle row really between boxes number three and four. And when it comes to thinking
about hominin meat-eating the main way to investigate this is through the study of animal
fossils with butchery marks including cut marks made from skinning, disarticulating and defleshing animals, as well as percussion marks
left by bashing bones open to get at the fat and calorie-rich marrow. I also study tooth marks and other chewing damage
left by carnivores. The lens I use is literally a hand lens, like a simple magnifying
glass that I can use to identify these marks on fossil bones. So I’m gonna take you
on a taphonomic timeline of what we know about
the earliest evidence for hominin carnivory. And the bulk of the evidence
for the earliest carnivory in human evolutionary history really comes from three sites in Ethiopia. The oldest is a 3.3 million
year old site called Dikika where a team led by people including Jessica Thompson
and Shannon McPherron discovered just a handful of bones including those pictured on the left with possible butchery marks on them. Two other sites from Ethiopia
called Gona and Bouri, the bones on the right
are from pictures of bones with butchery marks from Bouri. Those date to 2.6 and 2.5
million years ago respectively. They also preserve a handful
of butchery mark fossils. While much ink has been spilled about whether some of these marks are actually butchery marks and not marks made by
crocodiles, mammalian carnivores or other butchery mark mimics
like sedimentary abrasion, the importance of these sites is that they signal the beginning of a dietary shift in hominin
evolution to occasionally but apparently only occasionally, butchering and eating animals. There was a shift at two million years ago when we have the first evidence of both persistent carnivory and
early access to small animals and I’ll explain what that means. And the image up here is of
some butchered animal fossils from this site called Kanjera South in Southwestern Kenya. This is some research
that I’ve been involved in led by Rick Potts and Tom Plummer as well as Jennifer
Parkinson and Joe Ferraro At Kanjera there’s clear evidence from hundreds of butchery mark
fossil bones, animal bones, that hominins acquired and processed numerous relatively complete
small animal carcasses for meat and marrow. They got to these animals
first before other predators and butchered the meatier parts of them, so that’s the early access part. The Kanjera hominins also had at least occasional access to meat and marrow from larger-sized animals, an important difference between
this and the earlier sites where we do see evidence
of hominin butchery is that there’s evidence
for hominin butchery on bones at Kanjera from
three stratigraphic intervals that span hundreds to thousands of years. So hominins were coming back to this place in Southwestern
Kenya over and over again over a long period of
time to butcher animals. This is what persistent carnivory is and this gives us a sense
that this dietary behavior is becoming more important or at least it’s becoming
more commonplace. Just a little bit later in time a work led by David
Braun in a place called Koobi Fora in Northern Kenya, there’s evidence for
hominin butchery marks on turtles, crocodiles and fish. So at this time hominins
are already broadening their butchery behavior to include both aquatic as well as terrestrial animals. There is another shift that happened about one and a half million years ago. From several different bone assemblages from the sites of Olduvai Gorge some of which date back to
about 1.8 million years ago and Koobi Fora some of which date back to 1.5 million years ago led by a variety of different teams, there’s evidence from the skeletal parts that were transported and
butchered at these sites hominins had early access
to large animal carcasses. Basically they were now able
to get to these carcasses first and butcher the meatier
parts of large animals. The photo up here is a butchery marks on one and a half million year
old fossil antelope leg bone from Koobi Fora in Northern Kenya and this is part of an
assemblage that I studied and excavated as part of my dissertation. So, you’re probably picturing hominins striding out onto the African savanna armed with their stone-tipped spears getting ready to hunt these animals. Like this bronze sculpture
reconstruction of a Homo erectus from the Hall of Human
Origins at the Smithsonian carrying a goat-sized gazelle on her back. Well the earliest solid
evidence for hunting technology doesn’t come into the record until half a million years ago with the spear points from
a site called Kathu Pan in South Africa that have what are called diagnostic impact fractures on their tips indicating that they were definitely used as the ends of weapons. It’s possible that hominins were hunting with unmodified rocks or
sharpened sticks made into spears maybe like the Fongoli chimpanzees or other basically
archeologically invisible tools but we haven’t figured out
a way to detect this yet in the prehistoric record. And this is particularly likely in the case of the small
animals at Kanjera, so many of the small animals
themselves were juveniles and very young defenseless antelopes are often stashed in thick grass clumps for several weeks by their mothers, and doesn’t take very
sophisticated technology to basically walk up to
those little antelopes and bop them on the head
and then you have dinner. So what made early human carnivory or early hominin carnivory unique particularly compared to the possible diet of our earliest ancestors, as well as the diets of chimpanzees? There are four things. The first is that it involved big animals. And so, animals much
larger than themselves. As you heard from the talks earlier today, chimpanzees don’t hunt animals that are larger than themselves. This is a really useful reconstruction of an extinct elephant being butchered by a group of Homo erectus based on a one million
year old archeological site I’m involved in studying from
a Smithsonian research site in Southern Kenya called Olorgesailie. The second thing is that
it involved tool use and rare occasions including
the Fongoli chimps aside, we don’t think that our earliest ancestors necessarily used tools when they hunted. Hominins also don’t have the sharp teeth of mammalian carnivores
to be able to get through the skin of large animals, let alone slice meat off of their bones and bash them open to get marrow. It also likely involves something called deferred consumption which is basically not
eating something right away as soon as you find it. This is a weird thing that humans do. We don’t go to the grocery store, sit down in the middle the aisles, open the packages and start eating, I guess unless we’re really hungry. But in the earliest record
of hominin meat-eating we have evidence that hominins
transported carcass parts to central places for some
kind of communal consumption potentially food sharing. So if early humans were
eating meat from large animals for about two million years
before we have evidence, good solid evidence
for hunting technology, how were they getting access to them? One suggestion is that they
were scavenging the leftovers from large carnivore kills and I should point out
that this is something that is very rarely seen
in chimpanzee behavior. Chimps don’t seem to look at dead things and think of them as food, things that are already dead. So does scavenging look like
behaviorally and ecologically? There have been two
main kinds of scavenging that have been proposed
for early hominins. The first is called confrontational or aggressive or power scavenging. This is when hominins actively
chase carnivores off of kills presumably getting access to a lot of meat and
marrow in the process. There was probably a pretty
high risk of injury or predation of the hominins themselves
when they did this. And there are a few hominins with bite marks on them from carnivores to indicate that this did
happen at least occasionally. The second is passive scavenging and this is waiting until carnivores are completely done eating a kill, they’ve moved off, the scene is safe, hominins could go in
and eat the leftovers. One of the main criticisms of
the passive scavenging idea is that there probably wouldn’t
be much worth going after when carnivores were
done eating their fill. But is this the case? I decided to try to answer this question by simulating passive scavenging in a modern African ecosystem similar to those in which our earliest meat-eating ancestors lived. And I’m very happy to leave simulating confrontational scavenging
to somebody else. (audience laughing) So is passive scavenging worth it? The research I’ll be talking about here was part of my dissertation and it was published a few years ago in the Journal of Human Evolution. In 2002 to 2003, I spent
seven months in a game reserve in central Kenya called
Ol Pejeta Conservancy which you can see here on
a zoomed in map of Kenya, and I simulated passive scavenging. I specifically chose this
conservancy, Ol Pejeta, because the felid, the
the carnivore community is dominated by lions and most models of hominin scavenging are based on interactions
with large felids including lions, leopards
and extinct saber tooths. There have been a few
other scavenging studies that were done before mine but these were done in the Serengeti and Ngorongoro ecosystems of Tanzania, as well as the Maasai
Mara ecosystem of Kenya that’s actually all one big ecosystem that happens to be separated
by an international border. But these ecosystems have unusually high numbers of predators and particularly high competition
among predator species. So I was interested in going
to a felid-dominated ecosystem to simulate passive scavenging. Ol Pejeta is an African savanna ecosystem, it was about a hundred square
kilometers when I was there. It was called Sweetwaters
Game Reserve when I was there. Now it’s been expanded to
almost four times that size. And here you see some images of what it looked like there. It has mixed grassland
and woodland vegetation, all the photos on this slide are photos I took in the reserve. The vegetation map on the top left shows open grassy areas that are in black. They generally run east to
west on kind of high plateaus. The photos with the giraffe with the zebras in the background are a good example of what those open grassy areas look like. There’s a permanent river
called the Ewaso Ng’iro that runs north south through the reserve. You can see that on the western side with that green strip. That green is basically
riverine vegetation, trees particularly dominated
by yellow fever acacia or acacia that’s xanthophloea. There’s a picture of
that on the top right. The dominant bush in the
ecosystem is called euclea. This is noted in the bright blue areas, you can see that on the top middle. Whistling thorn acacia
or acacia drepanolobium are also very prevalent, those are noted in light
blue on the vegetation map. And the yellow and pink areas on that map are areas of mixed bushland,
woodland and grassland in kind of different proportions. The predator community
during the time of my study was dominated by lions
as I mentioned already and the herbivore community
was dominated by zebras followed by warthog,
impala, buffalo and baboon. So, my study methods were pretty simple. After finding out about a carnivore kill from a variety of sources I would wait until the lions
were completely satiated like this one in this photo with a distended belly full of warthog, this was a really happy sleepy lion, and I would document what
was left on their kills. I had two advantages over
my earlier ancestors. I had a four-wheel drive vehicle and I had an armed guard
with me at all times lessening the likelihood of me becoming one of my own samples. (audience laughing) In the time that I was at Ol Pejeta I collected 24 kill samples from several different
species of carnivores which you can see in the
left column of this table but I’m gonna focus particularly
on the lion kills today as that’s my largest sample and the most relevant for thinking about models of hominins scavenging. I separated the prey
into two size divisions related to how we classify
the size of animals when we’re doing archeological analysis, but here I’m just generally
calling them large or small. Larger animals are over 250 pounds, small animals less than 250 pounds. I documented the location and estimated the amount of meat left over
after the lions had their fill and here are some examples of what these leftovers looked like. The top right is a
picture of a zebra ribcage with quite a bit of meat left on it and the bottom right is a
picture of a part of a limb of a young Grant’s gazelle
with hardly any scraps left. And I should say specifically that I followed previous
researchers in defining bulk flesh as masses of muscle more at least 10% of their original size, flesh scraps were usually pieces of flesh less than size of the palm of your hand but over two to three centimeters and weighing more than
about a third of a pound. So how much meat can a scavenger eat from a large animal, something like a zebra
or a large antelope? I’m gonna walk you through
the axis of this graph before I show you the data. So the x-axis is a
skeletal element or bone arranged in groups from left to right with the total sample size of each bone listed in parentheses. The important part is the left two bones, they’re bones of the hindlimb, then bones of the forelimb, then bones of the torso and all the way on the right
are bones of the head and neck. The y-axis is the
proportion of those bones in all samples with three different levels of flesh availability, and I basically colored
them like a traffic light. Green for bulk flesh, yellow for flesh scraps and red for no flesh. So what did I find? You see a lot of green
and yellow on there. In large kills over 50%
of bones were abandoned with large muscle masses
still on them in green and 95% of the bones had either bulk flesh or flesh scraps which you see in yellow. That’s from large prey. Small prey is a different story. Only a single bone on smaller lion kills retained bulk flesh on it. About half the bone still
had some flesh scraps and the other half were totally defleshed, you can see that in red. And one take-home from the study is that if you’re an early human scavenging from a lion kill, the size of the prey really matters. So, how does this translate into actually how much meat a scavenger could eat? We can use weights of
adult wildebeest and zebra which are pictured here. The hindlimb of wildebeest
yields about 19 pounds of meat, a zebra about 50 pounds. A defleshed hindlimb of a wildebeest would be about two pounds, defleshed zebra about five pounds. That’s only a single hindlimb. A defleshed wildebeest carcass could yield 12 pounds of meat. A defleshed a zebra
carcass could yield about 34 pounds of meat. So if we estimate a four
calories per gram of meat this is about 2,200
calories from a wildebeest and almost 6,100 calories from a zebra and these are defleshed. So, translating this into
things we can understand here that’s about a little
more than five and a half In-N-Out burgers worth of
meat from a wildebeest, a little more than 15 and a half in burgers worth of meat from a zebra. I’m using an estimate of somewhere between 2,100 and 2,300 calories per day required for Homo erectus. A defleshed wildebeest is pretty much your daily caloric requirement. This is even without breaking the bones to get at the marrow inside. So the main take-home message is that I think scavenging from even relatively defleshed carcasses would have been a profitable and worthwhile activity for hominins. I just want to acknowledge
Government of Kenya, the funding, my PhD advisor and the people and the predators and the prey of Ol Pejeta. Thank you. (audience applauding) (uptempo music)

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  1. Hmmm…her hypothesis has merit, however…I wonder if she has factored in eating and hunting behavior of felids and other scavengers

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