CARTA: The Role of Hunting in Anthropogeny – Margaret Schoeninger Alyssa Crittenden Richard Wrangham

CARTA: The Role of Hunting in Anthropogeny – Margaret Schoeninger Alyssa Crittenden Richard Wrangham

October 12, 2019 38 By Stanley Isaacs


– [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. – The thing about humans… If you haven’t thought
about it, I’m sure you will. We can and do eat anything. So, what we can do is eat directly. So, we can be completely carnivorous. We could be almost completely herbivorous. If we can’t eat it, like grass, we feed it to a cow who can eat it or we do what Pascal does, which is takes the yeast
and makes bread out of it. So, we can also take that cow and cook it so we can actually get
something out of it. I just picked this slide at random. This is not one that I think
depicts much of anything. But the only reason I’m showing it is because I want you
to get sort of an idea of what the body size of what we’re going to be talking about. None of these animals are small. Okay, so, what did they eat? Well, how do you know? So, one of the ways is to do
morphological comparisons. So, what you have here is the skull of a very robust
Australopithecine on your right and you’ve got a very early
archaic hominin on your left. You can see that there’s
a massive difference. This is a chewing muscle
that goes through here. It has a ridge on the top of its head where there’s musculature
that goes all the way up. It is a chewing machine. These are the teeth. So, you see the size of these teeth versus the size of another fossil, Australopithecus africanus,
compared to a modern human. So, you can see the
different sizes of teeth. There are people in this room who do that. I don’t. But I can do it in general. Okay, what did they eat? You can also look at force and strength. You can look at… Use a model. So, what you got here is a macaque monkey. This is done on a macaque monkey skull. This is not done on a live macaque. I don’t believe. Although, those were
implanted in macaques. This is an Australopithecine
or a cast thereof shaped exactly like you would
a live one, if you could. And you can see where the
stress and the strain is coming. So, what you’ve got is a
lot of stress across here, which is where the chewing musculature’s gonna go back behind here. And so, you can see that
the distribution of stress in some places is the same. In other places, it’s not. Because what we’re looking at is strain deformation of
the bone following stress. Another way of looking at it is microwear. That’s what these pictures are. This is work that was down by
Mark Teaford and Peter Ungar. And what they say is
“gorilla fine wear striae, baboon-like pits, microflakes, and it shifts to hominid
puncture-crushing.” That tells you a little bit about what kinds of textures
these animals were eating, but it doesn’t tell you what they ate. Well, I like to go to
general principles first. So, although I’m not
gonna give you models, I’ll give you some general principles. One of those is, as body size increases, metabolic rate decreases. Per kilo, that’s not overall energetics. So, for small animals, they have to eat small packages of high quality food that could be processed quickly. So, you think of that galago monkey. Galago prosimian. You look at a large animal. Lots of low quality food
processed more slowly and they tend to be more sedentary. And, again, it’s not
total output of energy or total input of energy, it is per kilo. Well, okay, so, from that, let’s look at what primate
foods are all about. Primate foods break down into
sort of three categories. Insects, leaves, and fruit. So, what you’re looking at
are things that are insects. They move around a lot, but
they’re high in protein. Leaves are also high in protein, but very difficult to digest. And they also are seasonal. So, they will disappear. And so, they actually move, but over time. Fruit is high in energy. I almost showed you orangutan fruits that do not look like
they’re high in energy. But most fruits are high in energy and they’re easy to digest. They are, however, like
leaves, mobile in time. They come seasonally. When you look at the
primates that feed here, you have small primates,
very small primates, that can feed on insects. Again, requires small packages of food, but highly easy to digest. You have large primates,
depicted by this gorilla, again high in protein,
but very hard to digest. And gorillas don’t move around as much as the Microcebus does. I show you fruit. Although there’s no animal
that can survive just on fruit, because you don’t get the protein content. But I show you some monkeys that are gonna be feeding on fruit. You look at what these animals do do is you get animals along the
lines of frugivore/folivores. So, the large animals will be leaves and then they combine that with fruit. Small animals will either
be totally insectivorous or they’ll combine that with fruit. What you never have is a primate that relies on leaves and insects. And that’s just because a large animal cannot capture enough insects in order to be able to survive itself. Or able to survive. So, we look at this. In our body size, we should
have been a frugivore/folivore. Okay, well, you know what your diet is. And I would say that this has
been going on for a long time. We were not folivores. Not for a very long time. So, what do we do now
about what do they eat? Alright, this is the part that
I will be presenting today. And the data that I will present. And this has to do with stable isotopes. Stable isotopes are different forms of the exact same element. And the one I’m going to
be talking about is carbon, because it’s going to
be in a mineral portion of enamel or in bone. And you don’t get any
kinds of organics in that. So, what these elements… How they differ are different masses, which means that they
react at different rates. And that means that, if you’ve got something that reacts at different rates, that it can be distributed differently at certain trophic levels across different parts of
the same trophic level. And that’s what we’re gonna be doing. We present that as C13, C12. Those are the two stable isotopes. You’ve probably heard of carbon
14, which is radiocarbon. This is not a radioactive element. And so, isotope. Then you get them presented as delta C13. And it’s in per mil. Just to make it… Where you take a standard. You take your sample. You compare them and the
difference is the delta. Okay, how did this all get started? Well, we know that atmospheric
CO2 is taken up by plants by photosynthetic pathway. In 1948, we knew that
there were plants that the way in which they took up CO2… And I have to say that there is a man who was at UCSD when I got
here who was one of the men who discovered this. C4 plants, I’m not even
gonna talk about them, because that wasn’t on the UCSD. But they weren’t even
identified until 1967. So, we’ve had almost 20 years where people thought everything was like this. Now, what we do now is
look at the geochemistry. Well, Samuel Epstein, who was at CalTech, in 1971, finally had his aha moment when he realized that
all those plants that he had been collecting across
country and everywhere else and he could make no sense of it, because they came out with
a bimodal distribution. Lo and behold, these were two different photosynthetic pathways. Those two photosynthetic pathways are actually different kinds of plants. So, what you get here are
what we call C4 plants. They’re gonna be arid season grasses. Some sedges, not very many of them. And many of the succulents
have the same numbers, even though they’re not C4. They come out to be about a minus 12 compared to atmospheric
CO2, which is minus seven. And it’s different than
it was in the past. So, we have to correct for that. C3 plants actually take up
their material differently. They fix in a three carbon sugar at first. They come out to be minus 26. There is no overlap between C3 and C4. These are primate foods. These are leaves, fruits,
seeds, herbaceous plants, all those kinds of things. Those are primate foods. These are not primate foods. Alright, so, but we’re not
interested in the plants. We’re interested in the animals. We’re gonna try to figure
out what the animals do. The first lab study was by one of Sam Epstein’s
postdocs, Michael DeNiro, that was actually my postdoc advisor. And so, at CalTech, what
they did is they took grasses and they took plants that had a C3 pathway and they fed it to lab rats. And what they discovered was that these two actually mimicked
the plants that they ate. So, they actually could
see the difference. The one issue was, “Okay, but we don’t
know what the plants are when we’re looking at these things from the Pliocene, the Miocene,
and even the Pleistocene.” Well, okay, you’re gonna get a number, but what does that tell
you about what the plant is or what’s going on? You know, at this end, that’s C4. You know, at this end, it’s C3. What do you know about this? How is it offset from the diet? And what we found in this study is that the offset is about 10 per mil. These are animals with simple guts, just like you and I have. So, there was another lab study that was done on llama, of all things. And it was done, I believe,
at the University of Utah. And what they did is
they looked at the offset between these large
animals and their diets. Lo and behold, they are quite
different from one another. So, that means, if you’re gonna use what you thought was the
offset, which is minus 10, you’re gonna have problems
with an animal like a llama, a big animal, because
it’s not gonna give you the same kind of
information about the diet. This is the reason why. This is for one of the
people in the audience. What we have are cows,
which are unguinous, and they also are ruminants. They have a very basic stomach in the forefront of their other parts of their digestive system. And what they do is they house huge, vast quantities of microorganisms. And what they can do then
is they can actually ferment indigestible material. They are… Cows are nonselective feeders. If you look at the skull of a cow, it does not have any top teeth. All it’s doing is ripping anything up out of the ground and taking it. And so, all the bovids in East Africa are this kind of animal. The ones we’re gonna
compare to our hominins. Horses, on the other
hand, for those of you… If you live here, you know
exactly what a horse look like. So, I didn’t know that much
about horse digestive system until I was looking at
this to teach my courses. They also have a pretty
massive digestive system, but it’s all hindgut. It is not in the stomach. It’s in the hindgut. So, they actually are far
more selective feeders, because any toxin that comes in, which gets taken care of by
the ruminant’s microorganisms, cannot be handled by a horse. That’s why horses have such more sensitive diet requirements. If you look at a horse skull, it has both upper teeth and lower teeth that allows it to pick out
exactly what it wants to eat. These are primates. Those don’t look really anything
like either one of these. So, why do we think that we
can compare our primates, our hominins, directly
to browsers and grazers? Either zebra or to bovids in East Africa. If you look at all living primates… You’ve got a prosimian here. You’ve got monkeys. You’ve got an ape. They are all C3. If you look at Old World monkeys, whether you get a
ceropithecine, a colobine, what the baboons do, what
a duoc langur does in Asia, they are all C3. Does not matter whether they
have a large stomach or not. Baboons, in very marginal areas… I went through every study that
was done on living primates. And what you will hear is
that baboons can eat grass. Yes, they can. And about 5-10% of their
diet can actually be grass. And it’s only done in one marginal area out of five in Africa. You also get some poop that is C4, but, when you look at
their hair or their teeth, they are C3. So, now, let’s go to the fossil record. This is from Bernard Wood and I really appreciate him
allowing me to show this. What you have here are possible hominins. You’ve got what would be
called archaic hominins. And here you have the megadont. The ones that I showed you before. Then you get premodern Homo
and anatomically modern human. I will not be going up into this. I wanted to and I didn’t think there was gonna be enough time to do it. So, let’s look a little bit at the skeletons of some of these. I just picked some at random. Julia Lee-Thorp in South Africa
got us started doing this and has done a phenomenal job of preparing how you do enamel to do carbon isotope analysis. What I hope you see here is that all of these have flared rib cages. And Leslie Aiello once
said Lucy had no waist. If you think about it,
even men have waists. Because we have a small digestive system. We stand out. We have a small digestive system. These others did not. But they’re all hind gut fermenters. Because that’s what all of
us are and our relatives are. This is Homo ergaster, a
very early Homo erectus. And what I think you’ll see is that it does not look exactly like us. He probably had a waist. So, what we’re looking at is a different size digestive system. So, in 1999, Matt Sponheimer
and Julia Lee-Thorp published what I believe
is probably the first paper looking at carbon isotopes in early hominins to figure out diet. They came up with an average
of minus 8.2 per mil. Quote, “this early hominid
ate large quantities of carbon-13 enriched foods.” And, from their perspective, the thing that made them
on the human lineage is that we were eating C4 foods. Alright, what they did… And I hope you can see this in this slide. Is that they took the endpoint of C4 foods and they took the endpoint of C3 foods… And I’ll remind you this
is a foregut fermenter. This is a hindgut fermenter. It is not a simple gut. Any of them. So, what we have here is a
zebra and we have a gerenuk. But I could have picked
a bunch of other ones. Well, I don’t think you can
compare a primate to that, but that’s what they did. And then you take Homo… This was Australopithecus
africanis, I believe, at eight. And then they said, “Okay, well, it’s about halfway along the line. Massive quantities of C4 foods.” There is another way of doing this. And this is what I started looking at. And that is what if you think
about an offset of 10 per mil, which is what simple
gutted animals have now. We do, roughly. Or 14 per mil. What would be the difference in the diet? And what you have are the blue ones. The difference is if
you look at 10 per mil. And the green ones are the
ones if you look at 14 per mil. And I’m not saying that either
one of these is correct. It’s somewhere probably in between. And probably varies across
these different species. What I think you’ll notice is that virtually all of these have
low quantities of C4 foods if you buy my argument. Or they are actually C3 feeders, just like any normal primate would be. With one exception. And that is the very
robust ones in East Africa with the huge, massive chewing muscles. Now, this cannot be cited, but Fred Grind gave me
permission to point out that there is a new Paranthropus
at 3.5 million, which would put it way down in here. And it is a C3 feeder. If you look at it, it’s either a mix with very little C4 or it is C3. So, sometime, around one
million to 1.8 million, we ended up with a major shift
that those animals became C4. It was not true before that. So, I’ll finish up right now when we get to Homo
ergaster or Homo erectus. The same exact number as you
saw in the Australopithecine. But, here, I do not think we’re looking at mostly green plants. I think, here, we’re looking at meat. And we’re pretty sure. And I think we’re gonna
have some speakers after me. They’re gonna point out how
far back this probably went. This is one of Leslie Aiello’s. Again, human-like body shape. Probably the simple gut the way we do. I would say that probably
what we’re looking at when we have mixed C3
and C4 is probably a mix of hunting zebra and hunting
C3 feeding browsing animals. So, my conclusions. If we consider variation
in diet to appetite, which most people don’t, in modern fauna, the
diets in early hominins appear far more varied than
originally appreciated. If we consider metabolic differences between animals with simple GI tracts, which most primate, all primates have, and those relying on
extensive fermentation, alternative diets become
distinct possibilities. Now, thank you. Oh wait. One last one. I just want to say I have
to thank my students, because, if it weren’t for my
present and former students, you would not have heard this talk today. (applause) – The world loves meat. Each one of us in the US eats about 200 pounds of meat per year. Which makes us one of the top meat consuming countries in the world. And it’s more than twice
the global average. So, we are a nation of meat eaters living in a world of meat eaters. And global meat
consumption is on the rise. But the question is are we, as a species, inherently vegetarian or carnivorous? The answer is that we are both. Our species evolved to
consume an omnivorous diet that contains both plant
and animal products. But, today, I’ll be giving
you a very brief history of our species’s relationship with meat. And I have been tasked with the job to outline the nutritional benefits and costs of eating meat. Man the Hunter. The statement is a
catchphrase of our species. It conjures bold images
that have dominated academic discourse, the media, and public opinion for decades. Here, a popular artist named
Banksy plays with this idea in his piece The Trolley Hunters. And I urge you to do a search for Man the Hunter on the Internet and view the type of images that pop up. There are tens of millions of images. And most of them are a
variation on a theme, as you might imagine. The individual images and their content are not what’s important. It’s the underlying take home message. And that message is
that meat made us human. For well over a century, anthropologists have
touted meat consumption as the catalyst for
critical watershed moments in our evolutionary past. Things like pair bonding,
family formation, neural expansion, tool
making, and even cooperation. While the specific role
that meat might have played in the evolution of human
behavior is debated, one thing is certain. Meat did change the playing field for our earliest ancestors. So, our history with meat goes back quite far in our evolutionary past. And how far back continues to be debated. The image you see here dates to approximately 20,000 years ago. This artwork is found on the
caves in Lascaux, France. And, by the time that the artists were painting these images, it’s possible and likely that
early members of our genus had already been eating
meat for millions of years. Hunters living in the Paleolithic did not eat only muscle tissue. Much like contemporary foragers today, they consumed all of the animal. All edible portions of the carcass. Which would have included
organs, bone marrow, and even, in some instances,
the GI tract of the animal. Which is a practice called gastrophagy. They would have targeted game animals initially using stone tools with some early, though
controversial, dates putting the first stone tools in Kenya at 3.3 million years ago. Hafted or stone-tipped spears
came on the scene later with some finds in the
archeological record dating to around 500,000
years ago in South Africa. Bow and arrow technology later still. Possibly around 70,000 years ago. The important point here is that different complex technologies were created, modified, and
used to target animal protein going very far back in
human evolutionary history. So, the question of when
is a bit tricky to pin down and is something we’ll
be talking about today. The question of why our
ancestors turned to meat is slightly less contested. This is a photo of women in the
population with whom I work. The Hadza foragers of Tanzania
who live in East Africa. And very rarely do we see or associate women with big game hunting. And so, I like to show this photo, because it highlights the
often very cooperative form that hunting in human
populations can take. And, on this day, a man
killed a cape buffalo and there was so much meat that all hands were needed on
deck to transport this meat from the butchery site back to the camp. And I was also conscripted to help. I am not on camera. I’m taking the photo. And I’m useless. And I was useless that day, as well. So, my portion had to be
carried in a backpack. It was humiliating. But it was helpful. And, as I’m not very efficient to carrying anything on my head. So, the backpack worked for the day. But, when I said all hands on deck, I meant all hands on deck. So, this begs the question
why all the effort? Meat is a concentrated nutrient source that is easy to digest. Depending on preparation. Which we will talk
about later today, also. It’s high in protein, niacin,
essential micronutrients, like B complex vitamins, iron, and fat. It has three major types of fats, trans-fatty acids,
cholesterol, and triglycerides that are comprised mostly
of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids,
which we often call PUFAs. Two essential fatty acids found in meat are linoleic acid, which is an omega six, and alpha-linoleic acid,
which is an omega three. These cannot be synthesized by humans. And so, we need them. They’re important for
brain growth and function. So, we must consume them in our diet. Additional important omega three PUFAs that are found in red meat include docosahexaenoic acid or DHA and eicosapentaenoic acid or EPA. These are essential during
pregnancy and lactation and have also been
shown to reduce the risk of some chronic diseases. Red meat also plays a role in preventing iron deficiency or anemia. And, around the world, iron is one of the most
common deficient nutrients. And this might be linked to the fact that it has low bioavailability. Which can be defined as the ease and speed at which a nutrient, like iron, makes its way from the food that we eat to the target tissue. There are two different
types of dietary iron. As you might have
interpreted from this slide, heme and non-heme iron. Non-heme iron is found in both plant foods and animal tissues. And this type of iron is poorly absorbed and has low bioavailability. Heme iron, on the other hand, comes from hemoglobin and
myoglobin that’s found in animals. And this type of iron
is very bioavailable. For example, while it only contributes to a modest 10-15% of total dietary intake in the diet of red meat eaters, it accounts for more than
40% of total absorbed iron. So, heme iron is also known to increase the absorption of non-heme iron. Which means that meat really
is the best source of iron that we can consume. It’s important, as delays in global brain function and motor function have been associated with
chronic iron deficiency. Heme is also involved in the distinction between red and white meat. Which is largely based
on the myoglobin content. Myoglobin is the heme iron that contains pigmented proteins which make the meat red in color. So, the more myoglobin,
the redder the meat. Beef has far more myoglobin
when compared to chicken, which is considered a white meat. And, if you were used to
classifying pork as a white meat, you’re probably likely to do so based on a very successful
advertising campaign from the late 1980s. The slogan “Pork, the other white meat” was created for the National Pork Board in order to boost sales to
compete with chicken and turkey. And the campaign was very effective. So, although pork is typically classified as a white meat in culinary context, it is most certainly a red meat when it comes to its
nutritional composition. And this is important. Because red meat has
certain characteristics that white meat does not. And these are often associated with negative health outcomes. Associations reported with colorectal cancer and other carcinomas, atherosclerotic cardiovascular disease, type II diabetes, and, potentially, other inflammatory processes, as well. There are many proposed explanations for these disease associations. Such as saturated fat, high salt intake, and environmental pollutants that may be contaminating red meat. Another mechanistic explanation is the metabolic incorporation of a nonhuman sialic acid called Neu5Gc. And much of this groundbreaking work is being down right here at
UCSD at the medical school in Ajit Varki’s lab. Sialic acids are a
family of monosaccharides that are widely distributed
in animal tissues and, to a lesser extent, other organisms. And they’re located at the
very distal end of sugar chains that are connected to the
surfaces of cells and proteins. We lost the enzyme synthesizing Neu5Gc in our evolutionary past. Yet trace amounts are
still found in humans. So, even though it’s a foreign
molecule to the human body, we incorporate small amounts from the red meat that we consume. Red meat contains very
high amounts of Neu5Gc. I did a postdoc in Ajit’s lab and played a very small
role in very large project that attempted to quantify
the amount of Neu5Gc in commonly consumed
foods in the human diet. And Neu5Gc is in all animal products. So, anything associated with red meat, which would include
dairy products, as well. Eating red meat or the
products of red meat allows for the metabolic incorporation of this Neu5Gc into human tissues. So, the immune system recognizes
it as a foreign threat and then produces
antibodies to counter it. So, repeated consumption of red meat can cause chronic inflammation, which has been known to increase
risks of tumor formation. Neu5Gc has been linked to cancer, as well as cardiovascular and
other inflammatory diseases. And all available evidence supports this. Including studies that have been done with mice with humanized sialic acids. So, despite these disease risks, red meat consumption around
the world is on the rise. As much of the world is protein deficient, red meat is a good source of protein. And not only protein, but also iron, which we’ve talked about. So, perhaps the solution, then, according to many nutritionists,
is just to eat less meat. The American Institute for Cancer Research recommends that we don’t eat more than about 18 ounces of red meat per week. If the world does continue its
upward trajectory, however, how will we feed an
expected global population of 9.7 billion by 2050? According to the Food and
Agriculture Organization of the United Nations, about 60% of the world’s
ice free land surface is currently dedicated to raising crops and providing grazing land
for the animals we eat. So, this is supporting
around 360 million cattle and 600 million sheep and goats. About 788 million acres are used almost exclusively for livestock. A recent census of agriculture by the USDA estimates that this totals up to about 40% of all of the tillable land in the US. And many food scientists argue that this level of production is unsustainable. So, sustainable alternative
feeds for cattle are now being introduced. Like microalgae, sugarcane,
or brewer’s grains, which are the solid residue that are the product of germinated
and dried cereal grains used to make beer. Diets are also switching to alfalfa, which reduces methane emissions in cattle. So, in addition to coming up with more sustainable feed for livestock, people are trying to come up with ways to make the entire food
system more sustainable. And some estimates suggest that, in order to produce one billion
kilograms of beef today, we’re only using about 88% of
the water that we did in 1970. And only about approximately
67% of the land. In addition to coming up with this more sustainable feed for livestock, people are trying to come with ways to just make the entire
system more efficient. And this effort extends to
reducing waste outputs, as well. So, the amount of manure, for example, has been reduced by 18% compared to 1977. And, in addition, the
overall carbon footprint per billion kilos of beef produced in 2017 was reduced by over 16% compared to the same footprint from the late 1970s. But, while they might be down, livestock still contribute
to greenhouse gas emissions. As of last year, in 2017, the FAO estimated that, globally, livestock contributes to about 14.5% of all anthropogenic or manmade
greenhouse gas emissions due to enteric fermentation and manure. Some estimates suggest that emissions may be similar to those produced by the transportation industry. Although this figure
is very controversial. Suggesting that cows might emit as much gas on Earth as vehicles. So, some in the agricultural industry caution that these are not
easy comparisons to make and other factors are, of course, at play. But one thing that conservationists and agricultural industry agree on is that livestock does contribute to a substantial percentage of greenhouse gases in the world. The agricultural industry
is making strides, however, to reduce gas output by introducing feeds that create less belching in cows, improving breeding in a way that animal health interventions
are done differently. And the FAO argues that, if herd sizes were to shrink,
based on these best practices, that would mean fewer, yet
more productive livestock. So, in addition to
belching and passing gas, cows also produce a lot of manure. It’s the endpoint of their digestion. And it also produces nitrous oxide. So, there are many
fascinating new practices being developed that are
turning manure into electricity. Electricity which is then
being sold back to the grid. So, the costs of meat production are high. And, beyond the environmental costs, there’s a segment of nutrition science, as well as animal rights activists, that are arguing for the elimination of meat consumption altogether. But, given the global rise
in consumption patterns, this doesn’t seem to be the
most likely future outcome. So, despite the nutritional
benefits of consuming meat, there are significant
health and environmental costs of consumption, as well. That being said, as
we’ll hear about today, our species has a very long
relationship with red meat. It is one of the hallmarks
of human evolution. So, the question I leave you with, and one that I borrowed from Ajit Varki, has meat in human evolution gone from a blessing to a curse? Thank you. (applause) – Okay, so I’m an old, low ranking male. So, that means I should
be good at hunting. But it kind of depresses me to think the measure of success is
how good a hunter we are. I’m a vegetarian. Well, almost. So, that’s what I’d like to be. But, still, it’s an important issue. So, let’s talk about this. So, I want to talk about the origins of what I’ll call the
human predatory pattern. And the reason I’m calling it that is because that’s what Jessica
Thompson and colleagues are calling it in a paper in
press in Current Anthropology. Emphasizing the fact that hominins are killing animals
larger than themselves. Chimps can kill animals the
same size as themselves, namely other adult chimpanzees. But they don’t eat them. And humans, of course, are
different in this respect. So, the standard kind of model, which is, in some ways, the justification for the material we’ve been
hearing about chimpanzees, is that you have a last common ancestor that was hunting in the chimp style. And then, out of that comes
the human predatory pattern. There are… A slight modification of that comes from people like the Jessica Thompson team. And, I think, Brianna. Where you can have that
chimp style hunting and then, in the Australopithecine era, they may or may not have
been hunting very much. Difficult for them to catch a red colobus. Not too many around in the Savannah. And get interested in
meat and animal products. And then, out of that, you get
an interest in fat processing from the marrow and other organs. And, out of that, coming
the scavenging and hunting. But here’s my point. All of this assumes that
the stuff is eaten raw. Well that conforms to conventional wisdom. So, conventional wisdom
sees Australopithecenes giving rise to Homo erectus,
then Homo heidelbergensis, and, finally, the finest
kind of human you can have, represented here by the
president of Harvard, (laughter) emerging out of the president of Yale. (laughter) And the point, of course, is
the standard story is that this was raw meat that was responsible for this big transformation. Nothing much happening
after you get Homo erectus. And that fire comes in some
time quite a lot later. And maybe that’s true. But I doubt it myself. I think that fire came in earlier. But what is certainly true is that raw meat is a difficult
food for people nowadays. It’s rare to find hunters and gatherers eating raw meat at all, as you see from a survey around the world. And, in Africa, there is no record of people eating raw meat. And, to the extent that we have data on what happens when
people do eat raw meat, which we have to go to urban raw-foodists, people who are able to survive
on supermarkets and so on, what you find, following
the red line here, is that raw food is a
great way of losing weight. It shows that you lose body mass index, quite predictably, by eating
a lot of your diet raw. And this includes both vegans and people who were eating their meat raw. And then the blue line shows you that raw food is quite a
good contraceptive, too, because, by the time you’re
eating 50% of your food raw, if you are a woman, then… Sorry, 100% of your food raw, then you have a 50% chance of having your reproductive system
totally shut down. And that is… Despite the fact that they’re eating just about as high quality of
raw diet as you can imagine. And having no seasonal stresses and so on. Okay, so, it’s quite clear
that cooking does something. It increases the energy value, we know, for starch and protein and plant lipids. Now, here is the fact
that you should remember beyond anything else that
I’m going to say today. Nobody knows what the consequence
is of cooking animal fats. We do know about cooking plant lipids. That increases the digestibility
of the plant lipids. You get more energy value out of it. But no one has done it with animal fats. Which is crazy. And, if you think about the fact of how much more delicious
a lump of suet is when it’s been cooked, then it seems very likely that your food perception system
is tied to the consequences, biologically, in your body. But the fact is that we’re not sure. So, it seems very likely that raw meat has got low value compared
to both cooked meat… I mean, that’s what we do know. And the point I wanna say here is marrow. So, what I really want
to emphasize here is that the consequences of cooking meat are very substantially beneficial. The consequences of cooking marrow, with its fat content, may be a bit less. So, we’ll think about this in terms of safety and palatability
and time to ingest. I’m not gonna talk about digestibility and the cost of digestion, because we don’t know anything
in terms of the marrow. So, that’s pretty crazy. One of the most important foods, probably, in human
evolution, fat from animals. And cooking, the signature
feature of the human diet. And yet we don’t know
what the consequences is of cooking fat for the energy gain. Alright, so, we know cooking’s
biologically important. We know it raises the food value. It probably does it differently
for different foods. I want to propose something that will annoy several of my colleagues. Which is that, before cooking, hominin meat eating was less important and hominin fat eating was more important. So, the first thing I want to say is about the dangers of
eating from a dead zebra that you happen to find there. It is disgusting. So, Sonia Ragir pointed
out some time ago that the meat is dangerous when you find it because of bacterial growth. And Alex Smith, in my lab,
did some nice experiments showing that, if you compare
the rate of bacterial growth on raw meat compared to marrow, then it grows much faster on raw meat. And whereas, if you cook it,
then it’s safer very quickly. And internal marrow is really safe. So, meat you can sometimes get away with cutting the outside bits
off and taking what’s inside. But, even then, it decays pretty quickly. And it is going to
remain rather dangerous. Which I think is why
chimpanzees, by the way, don’t scavenge much. There was implication earlier that they sort of don’t
recognize dead meat as food. I think they do. It’s just that they’re
pretty cautious about it. And occasionally they do scavenge. Okay, so, now here’s a major
point I wanted to make. That hominins without
fire couldn’t hunt much. ‘Cause there’s just not
much time for hunting. So, here is a data on the amount of time that chimpanzees spend feeding, which is incredibly frustrating to teams from National Geographic. They kind of want to see
chimps doing fancy things. ‘Cause, in fact, all
they do is just sit there eating most of the time. And there’s variation among the sites. And the ones at the bottom, Bossou, they’re eating quite a lot of human foods dug up from fields and that sort of thing. But, overall, we got
close on 50% of their day is spent literally just chewing. And that means that they
can’t do other things. Such as write poetry or go hunting. Here, what we got is a
slightly strange plot of the distribution of
the time spent feeding in nonhuman primates. And you see there’s a pretty steady rise as body size increases on the bottom axis. And so, by the time you are a Homo, you should be eating for something like, chewing for something like 50 to actually something slightly higher than 50% of the day. That’s what you should be doing. But you’re not. In fact, what humans do is they chew for less than an hour a day. It’s a relatively trivial time. And meat eating does not help that much if you are a raw eater. So, here are some estimates. It’s difficult to get normally for total time it takes to chew a carcass. Because it’s relatively
rare that you can see all the bits of the carcass and how much they have
been eaten by chimps. But this suggests that,
when you take, for instance, a baboon that weighs a certain amount and you estimate 80% of it was eaten. And you total up all
the eating that was done during that period. You can see, there’s a total
of nine chimpanzee hours. And the net result is that you’re eating meat at about the rate that you are some of the higher quality fruits in terms of calorie intake. There’s a note here saying
that Ian Gilby thinks that I’m underestimating the rate of eating. And I’m sure I’m underestimating it for the initial phase of eating where they’re eating the softer bits. But we have yet to get
very good data on this, so it may turn out that the
underestimate is important. But, nevertheless, that’s
what we got so far. Okay, so, chimps don’t hunt
for very long at a time. Here, you see some estimates. All between 15 minutes and half an hour. That sort of thing. If they get into a hunt. And, after that, there, they give up. And this is not affected by how often they’re overall killing. There’s this big range we’ve seen before. Sometimes one a month
and sometimes 10 a month. But, nevertheless,
they’re always just having this low rate of, this
low duration of the hunt. And you can see why. Here is how the feeding
time is distributed in a particular individual
from dawn until dusk. The red is when he’s chewing. So, there’s just not much
time between chewing. And, by the way, when they stop chewing, what are they doing? Mostly, lying around in order
to be able to digest the food. So, the typical pattern
is you go up into a tree. You eat for 45 minutes. And then you come lie down. And then wait for the stomach to be empty and then you go up again. That’s what seems to be happening. So, there’s variation among chimps. And here’s a bunch of different days. And you see, some days, there
is very, very little time to do anything other than eat. And sometimes more. And it balances out across days. And so on. But you can look at this and you can say, “Okay, let’s look at the
interfeeding interval.” How much time is there
between what you gotta do, which is to get food into your belly. And the answer is that
the median of 20 minutes, the mean of 40 minutes. This is old data from Gombe. But that compares with
the mean hunt duration of a quarter of an hour, half an hour. So, it’s about the same. And the implication here is that, if you are chewing a lot, there’s just no time to go hunting. So, sorry. Now, humans, obviously,
we’re much less constrained by eating time. And, actually, funnily enough, there is no paper that has
looked at when humans eat. But this looks like a very
confident assertion that, among hunter-gatherers, only one regular meal is eaten in camp and it’s at night after
people have returned from the day’s hunting. That’s sort of typical pattern as you go into the earlier ethnographies. So, humans are able to spend long hours during the day on the hunt. And here you see a distribution across different hunter gatherer societies for men and women. And the men are spending, on average, just over four hours a day. Which means that it is possible for them to do something that chimpanzees could not possibly do. And, therefore, I think that
a raw meat eating hominin could not have done, either. Well, meanwhile, so, could they go out and track around looking for their food? Foraging, hunting. Dan Lieberman and his colleague Bramble have drawn attention to
a whole bunch of features in our skeletons which indicate that Homo is uniquely derived in an ability to have endurance walking
or endurance running. Tramping around across the Savannah looking for opportunities to
either scavenge or to kill. Well, that doesn’t seem very easy if you’ve got a great big belly that we’ve been hearing
about with those flared ribs. And you’re keeping it full
of stuff all the time. So, you’re asking a gorilla
full of vegetation, as it were, to go running off for two or three hours. I don’t think so. I think one reason is
it’s got a large gut. And that large gut is full for a tremendous amount of the time. And then I actually think
there’s probably another reason. This is a little bit speculative, really. But I think that creatures before fire would have needed to keep
warm at night with hair. And, as long as they had to do that, then they couldn’t lose
heat easily during the day. So, it’s very difficult for me to imagine an endurance runner, in particular, being able to do that before fire. Okay, so, what I’m saying so far is that meat eating would have been less extensive before the control of fire. Because of the lack of
safety in the raw meat and the fact of chewing for so long meant that you had, also,
large guts full of food. You couldn’t run and hunt. And I suspect, when we know about it, that the relative value of
raw meat compared to raw fat is gonna be relatively low. Okay, so what did hominins
eat before cooking? Because I do think that
it’s reasonable to imagine that there’s been a phase in which hominins were using animal
products before cooking. And the safe bit are the ones
that are enclosed in bone. And that would be marrow or brain from below the exposed
surfaces is what you wanna do. And, certainly, marrow
is an important food for hunter-gatherers. Here is data for the Hadza and how many of them are eaten raw. So, by the time you’re eating
big animals, like buffalo, James Oliver finds that 80%, or 70-80%, of the limb bones are eaten raw. So, that all seems just fine. But there would be a difference if you’re eating them
raw from eating cooked. Because, nowadays, there is an ability to use both the marrow
in the shaft of the bone and the fat in the trabecular bone, or the cancellous bone area. Which you’re very difficult to
get at just with your teeth. You really have to boil it up to be able to release the grease. And, until you have cooking, you’re not gonna be able
to use that very much. And then there’s a difference in the kind of marrow that
is gonna be preferred. So, Binford showed very nicely that there is a good relationship between the degree of
unsaturated fat in the marrow and the preference. Here, you see, for the Nunamiut
people that he was studying, that the more unsaturated marrow there is, then the more the bone is preferred. So, unsaturated is much
nicer than saturated fat when it’s eaten raw. And that is probably because it has got a lower melting point. And, with a lower melting point, probably, I think it will turn out to
have a lower cost of digestion, because the body is going
to have to work less hard to reduce it to the tiny, tiny particles just a few angstroms across that have to be reduced before it can go across the intestinal wall. So, where are the unsaturated fats found? They are found more at the
nether ends of the limbs. So, if you take a typical ungular foreleg, you find that the saturated fats tend to be richer close to the shoulder and throughout the axial skeleton. And the unsaturated fats are
richer at the distal parts. Which nobody understands why that is. I mean, there’s the sort of suggestion unsaturated fats, having
lower melting points, they may be sort of more flexible. They may allow more flexibility. That’s a bit speculative. Okay, so, preference for unsaturated fats. And then there’s the question of brains. So, the limb marrow is
great for most of the year. But you see here, in a couple of examples, that femur marrow is very poor
during periods of the year when the animals are in poor condition. Going right down to 20% fat. And that’s a point
mirroring what’s happening with the kidney fat. At which you can expect there
will be rejection of the food. So, here’s claims from
Binford saying that, if the caribou is in too poor condition, you break open the bone
and it’s soft and runny, then goodbye. During those periods,
brains should be okay. Now, here is Kim Hill
saying that he loved… Well, he’s saying the Ache and the Hiwi, hunter-gatherers in Paraguay
and Venezuela, love brains. And he says, grossly,
that he loved it himself. I asked him if he ate it raw. He said no. But you could. As long as it’s reasonably fresh. There is decay that goes on there. Of course, the problems
with brains is that they’re hard to extract. And, if you’re a hominin,
they’re embedded very often with things with horns. And the skull is really heavy. So, it’s not that great. But it is good, because
the quality of the fat always stays high. It’s the last thing that
you will lose fat from. And then goodbye. (laughter) So, my conclusion is that, if the early Homo diets were raw, then you’ve got to put up with the notion that there was extensive chewing,
minimal time for hunting, and, I think, no endurance running. And they would be eating particularly from the fat rich areas. And there’ll be more marrow
than in cooked diets. There’d be more marrow
especially from the distal bones and especially from the brain. So, overall, more scavenging,
more fat, and less meat. Overall, the kind of concept
that I was referring to earlier of chimpanzee-style hunting giving rise to an interest in animal products and percussive fat-processing, breaking open those limb bones, and then, finally, getting
the human predatory pattern. That seems to me a great
way to think about things. And then we should think
about the first three stages as involving raw meat. But I don’t think you can
go very far into the fourth without making it cooked. So, I have a different concept of the Harvard and the Yale presence. Thank you. (applause)