Bipeds on the Serengeti

Dr. Josh Stout looks at the coevolution of our diet, our exercise and our consciousness. We start with the beginning of our evolution as we split off from chimpanzees.

Bipeds on the Serengeti
Photo by Hu Chen / Unsplash

We are going to be looking at the coevolution of our diet, our exercise and our consciousness. And we're going to start off with the beginning of our evolution as we split off from chimpanzees.

Eric 0:15
So. Josh, come on, sit down.

Friday, September 15th, 2023. What are we doing?

Dr. Stout 0:24
We are doing a podcast called Body Mind Evolution, and we're going to be looking at the sort of coevolution of our diet, our exercise and our consciousness. And we're going to start off with the beginning of our evolution as we split off from chimpanzees. So my name is Dr. Josh Stout. I'm a teacher of human evolution and Darwinian medicine and human physiology at Fairleigh Dickinson University. And I really think that we haven't really looked at the way consciousness has evolved along with the evolution of the body. And I think my students in particular have seemed very interested in how this affects our diet and our exercise and the way our body has developed over the last, say, 6 million years. And I wanted to start off the story with how we left the rainforest and went on to the the Serengeti and what that did to our physiology, how we developed as we became bipeds. So there's a couple of things that humans are particularly unique in our in our in our in our physiology. And one of those things is being a biped. But we have to think about what we were before that. So we were eating fruit. We were maybe traveling for about a mile or so every day looking for fruit as chimpanzees and everything was wonderful in the jungle. And then about 6 million years ago, the there was a tremendous increase in volcanic activity and the African continent started to rip apart, causing the huge up thrust of mountains which caused a rain shadow. And the jungle that we lived in started to turn into a grassland. And so suddenly we were thrown from being a sort of happy go lucky chimpanzees, if you could see it that way, into a group of primates that had to really work hard to get our food. We had to walk long distances or at first it would have been some sort of maybe all fours or knuckle walking.

Eric 2:43
How quickly did this transition take place?

Dr. Stout 2:46
Are it as far as the fossil record is concerned, basically instantaneously? So first there were there were chimpanzees and then there was a collection of things that could basically walk on two legs that were like chimpanzees, chimpanzee body walking on two legs.

Eric 3:02
This couldn't have happened in thousands of years.

Dr. Stout 3:04
Well, it's very unclear when the exact moment would have been There was everything from from could have started 12 million years ago. The consensus is around 6 million years ago. And we start seeing the first, you know, really convincing. There are ancestors in our line around 4 million years ago. So there is a 2 million year wide question mark where a bunch of different strategies are being tried. So some animals, some some early, early, early hominids are going to be walking on the tops of their feet. Others have really long toes so they can climb trees well, but they can't really run because they can't bend their toes. There's a lot of different things that are that are that are happening.

Eric 3:51
This is all happening in reaction to the changing of the land.

Dr. Stout 3:53
So now the whole point is, is that our food is now really spread out. We can't just go from fruit tree to fruit. Tree climbing is still important because as apes out on the Serengeti, we are

slower than everything else out there and everything can eat us. So climbing trees is really, really important. We spend a lot of time probably every night we're sleeping in the trees. We get up in the morning and then we have to walk a long distance. And walking became sort of central to what made us us over the next couple of million years.

Eric 4:30 Here we go.

Dr. Stout 4:31
Okay, So we we we evolved to this sort of continuous movement every day, four or five miles a day of walking, as opposed to less than a mile that the chimpanzees would have been doing. And then when we got to our food, it was going to be very different. Instead of just reaching up and plucking a fruit or climbing a tree and eating the fruit in the tree. Now, we had to dig for tubers. And so we actually have a very strong upper body that is evolved from the chimpanzee. So a chimpanzee can swing from branches. We can't swing from branches anymore because we don't have the fingers for it. Our fingers are have became shorter. We'll talk about that later. These ones still would have had nice long fingers so they could climb the tree very well. Some of them had long toes so they could climb trees, but that slowed down their walking. But the strong upper body with, you know. Good, good, good shoulder bones and I upper back strength meant that we could dig as well. And so even though chimpanzees don't do a lot of digging, we are pre adapted for that. We had we had a good musculature so we could pull up plants, We could eat the underground stems, we could eat the underground tubers and roots, and we started to change the physiology of our skull as well. So our jaws became much, much thicker with thicker teeth, thicker tooth enamel. Strangely, chimpanzee teeth are very sharp, but they have thin tooth enamel. They're not nearly as strong as ours. Ours are sort of flat. And we have, you know, molars that look like molars as opposed to sort of pointy teeth in the back of a chimpanzee's mouth. And so we became specialists at grinding our food and walking long distances. And so this is where I would say our need for both continuous exercise and fibre comes in. We became we spent most of our days either chewing fibre or walking, and our jaws became tremendously thick. Some of these groups were called Nutcracker Man. They had huge jaws that could crack through almost anything. Possibly some of it might have been used for scavenging. Anything that, you know, would have provided a source of calories would have been useful. So there might have been some dried meats, but there's not a lot of assumption that we were doing any large amount of hunting at this time. We would have been much more scavenging, digging roots and getting our calories, mostly from from carbohydrates, but in very complex forms. So in root form, basically no fire, no cooking, uncooked, uncooked.

Eric 7:10 Just mashed.

Dr. Stout 7:12
Chewed, lots of chewing. Yeah, a lot of chewing. And so we had ridges on the tops of our skulls where our jaw muscles connected. We had.

Eric 7:22
That's what that was.

Dr. Stout 7:23
About. Yeah. Yeah. And we had teeth there about two or three times the size of ours today. But the interesting thing is, you know, that thick tooth enamel we actually still have inherited. So we very much have kept that general physiology for chewing as much as we have for walking long distances. Now, obviously humans aren't the only thing that can chew, but we are definitely the only thing that can walk like bipeds the way we do. And so that has shaped a lot of our movement. Um, I like to think about sort of the, the, the, the mental map of, of, of, of the time

as well where we would have been in small groups. Chimpanzees can be as many as maybe 70 and a troop. And we probably would have been moving out on the Serengeti in small groups protecting a large territory as a larger group. So maybe something like small family groups working together. It's obviously speculation, but if you're imagining an ape with few natural defenses, there must have been some way to band together and work with each other. So this would have also been the beginning of

forming not exactly a society, but of working together to gain calories. As our brains are getting bigger, we can't survive without additional calories. The diet that a single female could gather for herself probably would have not been sufficient to feed her herself and a baby as well, and certainly not a baby and a toddler. So there would have had to have been groups working together to do some limited scavenging and digging of tubers and traveling under that under those conditions, usually 4 hours a day. And we became specialists at not using a lot of calories, which is part of the problem today. So we get so fat so easily because we have such highly tuned insulin systems that turns every calorie we get, if we possibly can, into fat stored fat, so we can get through these hard times where we've been stuck out on the grasslands and so we became specialists at not speed but endurance. And so we can walk further than chimpanzee. We can't outrun one. We can dig for longer than a chimpanzee, but we'd lose in an arm wrestling contest. So we lost strength and gained tremendous amounts of endurance and a whole physiology. That's dedicated to storing calories and to holding on to every calorie we can possibly get. And a physiology that essentially forces us to go out and get extra just so we can make it through the, you know, the hard times that are coming on. And it's actually interesting in there are parts of Africa where they've taken a series of of of sort of the average subsistence farmers weights over the course of the year. And you can see during the rainy season when crops are abundant, they'll gain a couple of kilos and then lose them again during the dry season. So we really were adapted for this kind of eating well, everything you possibly can when you can, and then just suffering and looking for more food while you while you can't find it. And so we would just walk and walk and walk till we found food, dig as much food as we could, and then just eat and eat meat and eat until there was no food left and then walk to the next place. And so this is in many ways sort of governed our attitude. We like to eat with other people. It makes us feel safer because we're in a group, are much less likely to have a, you know, saber tooth tiger come up behind you and eat you and.

Eric 11:18
To finish every single thing.

Dr. Stout 11:19
And we're inclined to finish every single thing. There's actually absolutely a social component of it.

Eric 11:24
And there's all sorts of contemporary psychology.

Dr. Stout 11:29
Yeah, yeah, yeah, yeah, yeah.

Eric 11:30
That, that that gets you to not do that.

Dr. Stout 11:32
Yes. Well, it's, you know, we would like to be mindful of what we're eating, but if you think about how we would first approach food, it would be just eat it. If you find it, eat it, It doesn't matter what it is. Eat it now quickly and move on, because there might be something else looking for that food, not least another one of our own species. Right. So we would have been

territorial. We know chimpanzee has war, so there would have been competition with other groups and there would have been, you know, a lot of possible strife if they found you with a high resource food item. So you would eat it as quickly as possible and move on. And, you know, that was very much our life. We would not have had any kind of permanent settlements, but we would have had a territory that we were roaming very long distances to guard the entire the entire territory, which probably would have had fixed resources. So our brains were slightly larger than chimpanzees, but we could imagine what was under the ground. We could we could imagine that it was growing. We could imagine when the rainy season came that the tubers.

Eric 12:37
Would be How did this capacity for imagination come? All you said is that we separated when we came out of the trees.

Dr. Stout 12:45
Okay? Every every mammal, in my opinion, can do a little bit of imagination in terms of predicting what's going to happen, you know, So when I'm if I start running in the forest, my dog immediately assumes we're hunting a deer, makes a break to one side or the other to try and outflank the deer and then drive the deer in front of me. So the dog is not correctly, but it is imagining what I want to do. Imagining the next move is to, to me, catch a deer.

Eric 13:16
Chimpanzees just weren't imagining about tubers on the ground.

Dr. Stout 13:19
They weren't thinking about that. What a chimpanzee brain was very good at doing was finding where the next fruit tree was going to be ripe at the right time. It didn't take quite as much knowledge as in your head imagining something under the ground. The other thing that chimpanzees are very good at doing and our ancestors must have been, would be that social component. So their imagination is often what is in the brain of another animal. And how how are you going to manipulate that other animal? It's it's called the sort of Machiavellian intelligence hypothesis that we evolved to both learn how to lie to each other and successfully lie to each other. And chimpanzees have done this. So, you know, one of the early conversations with Koko the gorilla, I guess I Koko, pooed inside her trailer. And then when the handler came up to Koko and said, Why is there Pooh in the trailer? Koko said, It is this. This homeless guy came in and he put in the trailer. And so, you know, lying is something that's very, very deep in our evolution, but also detecting, lying, knowing when someone has has has lied and.

Eric 14:29
It would go together.

Dr. Stout 14:30
But beyond that, you are able to manipulate whole groups, right? So if there's a troop up to 70, 80, 90 other individuals in your troop, you need to have relationships with all of them, know how they are being manipulated and how they're manipulating you. You need to make alliances. You can't do something on your own. You need backup. So Jane Goodall, working with the with the chimps, I do not only discuss them, you know, going to war, but so much more of their time spent grooming each other, making making associations with each other. Now, we don't know when language started. We don't imagine it was particularly advanced at this point. It would have been probably similar to what you would have seen in chimpanzees. So gestural, maybe a few vocalizations. But over the course of her evolution, all of those touch interactions that primates have, we would have kept that as as a as a basic need and then added language interactions on top of that. So the social interaction is vital to our well-being

so that it we we need to touch each other. We need to communicate with each other. These are these are in some ways similar in our modern brains. Chimpanzees is all about the touching, you know. So if if a chimpanzee is sad, it will turn his back so that you can scratch its back. And humans need that same kind of interaction. And it's something that I really feel we are having problems with in our society. The the the lack of touching and interaction.

Eric 16:00
Yes. The the the epidemic of loneliness is.

Dr. Stout 16:02
And, you know, particularly among men and older men, this is this is happening. And, you know, it's it's very difficult because obviously a guy can't just go out and touch people. He will definitely get in trouble. Wouldn't work. It wouldn't work. It would be a bad idea. But we need this as a species and we can make do with with conversation a little bit, right? Just having a conversation with someone fulfils a lot of of those needs. But the touch is also a sort of underlying physiological need that, you know, it releases, you know, oxytocin and hormones that help relax us. And I are stress hormones go down. So you the corticosteroids are lowered in response to touch. And so without these things we we have more stress and these are these are part of our physiological evolution. But all of our conscious evolution, right of consciousness is not just evolved about, you know, how to play chess or something like that. Consciousness is the entire suite of interactions that we have with ourselves in the world around us. And we tend not to think of the consciousness, particularly of other animals. We tend to think of, you know, ourselves as the only conscious creature. But, you know, just as I was saying that, you know, Koko, I figured out a way to lie. I was lied to yesterday by a blue jay, and Blue Jay was sitting in a tree and wanted me to come out where it could see me better. I was I was sort of sitting on a porch behind a couple of bushes, and the blue Jay wanted me to come out and stand in the open. So it went to a tree that I couldn't see. Just around the corner, started imitating a hawk. And it combined a couple of hawks, and it sort of was a red shouldered hawk, plus an osprey. So it sounded like a hawk, but not one I knew sort of doing a cat hair care character and then sort of a hawk call and combining a couple of calls and then switching into Blue Jay angry at a hawk call. So then I got a guy got back at the hawk. So it was doing both sides of the fight. It was doing the hawk and it was doing the blue Jay Mad at the Hawk for you, for me. So that I then stood up, walked around the corner to see what this hawk was doing in the tree out, flew the blue. Jay flew directly at me, looked me in the face ten feet over my head and went and flew into the woods. Now, if I hadn't been paying attention, this wouldn't have worked, right? So if I'm not listening for what Blue Jays say, they can't lie to me. But as soon as I start thinking about the world of animal communication, they're communicating all the time, you know, just like, you know, your dog, your cat might be communicating with you. The rest of the world is. So I don't think communication at its sort of basic level is something brand new to humans. I think very few of our our behaviors are unique to us, but we've taken many of them up to a much higher level. So obviously our linguistic ability far surpasses that of my dog or, you know, your cat or something. And it's somewhat the same strangely with bipedalism. You know, bipedalism is a way of getting from place to place. And we generally think of ourselves as so much physically weaker than all the other animals. And it's true, but there's nothing that can come anywhere close to us. So, for example, there is a.

Eric 19:25
You mean in terms of.

Dr. Stout 19:26
In terms of endurance.

Eric 19:28


Dr. Stout 19:28
Sheer getting from one place to another. So there is a race in Australia that pits humans against horses over something like 40 miles, maybe it's 120 miles. It's really far and humans often win.

Eric 19:43
You mean one human against one human riding a horse? Yes.

Dr. Stout 19:47
And humans often on their own, not on a horse, will win this race because our endurance is even surpasses that of wolves. Now, a wolf can obviously outrun you, but talking about just jogging for days, not that I would want to do it, but there are humans out there that can do it even beyond what a wolf would be able to do.

Eric 20:08
So you're saying we're built to survive?

Dr. Stout 20:09
We are built to survive, live and exercise in a way that maximizes our ability to travel on the fewest possible calories. So we need exercise, but we don't burn calories very quickly. We need calories and we store them really well. So everything is stacked against us in terms of how much exercise we need.

Eric 20:34
We're built for a consistent but not very fast movement.

Dr. Stout 20:40
Yeah, in many ways, I think of us as sort of chimpanzees, poor relations chimpanzees I was mentioning, have a pretty easy life. But during the dry season, chimpanzees are going to have to walk further. They're going to have to start seeking out new forms of calories. They might even start hunting a little bit. You know, they'll they'll they'll they'll take a stick and jab it into a tree hole to see if there's anything in the hall and then pull out the piece of meat and share it that way. You know, they talk about prostitution as the oldest profession, but you can see it way back in in in the chimps. The only time a female is likely to ever get meat is from a male in exchange for mating opportunity. So the males almost never share the meat, but they will in a very sort of barter kind of relationship. And so this is also built very deeply into our into our consciousness. And so why would the female be willing to do this? She needs a supply of extra calories to help. You know, I developing fetus or an infant. And chimpanzees will also build relationships like this. So there will be an alliance between males and females in exchange for feeding future mating possibilities, even if they're not. She's not in estrus at that time. Humans are truly strange when it comes to reproduction. We're one of the few creatures that the females fool us into thinking they are receptive all the time and they actually can, you know, become pregnant quite a bit of the year right. So, so out of every month, you know, two weeks or so, they're receptive and it's hard to tell that they're not the rest of the month. Whereas chimpanzees get a giant sexual swelling that is obvious from across the room and every every male knows it. But they will, knowing this period of time is coming up, will make alliances with males. So that they can then choose the male that they get to meet with. And not just every male in the troop, which is how most females end up starting in the chimp groups. So, you know, this is another thing that is is is deeply part of our consciousness, is understanding that alliances need to be made to provide resources for children and for, you know, for offspring, and that sexual relationships are absolutely part of these alliances. But they might not employ sex immediately. Right. The sex might be implied in part of the entire alliance

arrangement that's going to include things like food and resources and grooming each other and spending time with each other done by chimps.

Eric 23:25 Sounds language.

Dr. Stout 23:26
Yes. Yes. All the the language we have at that point would be, you know, vocalizations, facial expressions, you know, gestures. You know, this different different things to call another chimp over, but very much holding the entire group together based on this system of alliances. So, you know, consciousness is something that builds up in stages and pieces. So we don't know what the first hominids out on the Serengeti would have had as a consciousness. But we can assume that they had everything that the chimpanzees had, maybe plus a little bit extra because their brains got slightly bigger and they would have had to do a few more things. They probably had to have a larger territory that might have meant a larger group protecting that territory. They probably, you know, they undoubtedly would have had to have a larger mental map of their resources just to know where things are going to be at the right times. They have to have a good sense of the seasons, right. They have to know what's going down, the rainy season, what's going to happen in the dry season. These are very, very different times in Africa. And if you're in the wrong place, you're not going to survive. So you have to be in the right place at the right time. It's not just the places. So all of these things are part of a developing mental map, development of consciousness, understanding what's happening in other people's brains, understanding how it's like what happens in your brain. So how do I lie to this person? How do I manipulate them?

Eric 24:51
That's some advanced imagination, imagining what's happening in someone else's brain.

Dr. Stout 24:56
But it's what, you know, the Blue Jay was doing imagining what's in my brain. It was, you know, it could have been wrong if I wasn't paying any attention. It would have just been making calls off into the trees and just a bird. But because I was listening, it imagined I was listening and it happened to be right. And then it was able to fool me, you know? So there is, you know, I when I was traveling in in Java, there was a troupe of macaques in the rainforest, and we were we were walk along in the rainforest and they tried to get me to give them my garbage. So we'd had a little picnic and it was there was, you know, a bag of food. And the macaques wanted the garbage. So they start off with a mother holding her little baby, and she's showing me the little baby, trying to get the food from me by manipulating me. And she absolutely had a model in her brain of I would give her food because she had a little baby. And, you know, I'm like, get away from me, you parasite. And, you know, keep walking on. And the next, you know, it was like, you know, the three trolls or the three billy goats gruff kind of thing. So the next one that comes is a is a full grown, dominant male macaque with a really large fangs, which he shows to.

Eric 26:18
Me they can be intimidating.

Dr. Stout 26:19
And big muscles, which he's flexing and he and I'm like, let's go. And and I get ready to kick him if he if he comes at me.

Eric 26:29
There was no rock available.

Dr. Stout 26:30
That that Yeah that's later in the story but yeah he backs down and then a few more feet there's another one large big macaque now and I do the same thing and I'm putting the food bag behind me, but now they've predicted me so they run up my back, slash the bag of food. Everyone grabs a piece and there's like six monkeys, and then there's no monkeys and there's no food. And it was all over in a blink of an eye. And they had completely predicted my actions and outsmarted me. And, you know, they they had a mental.

Eric 27:06
Map on this again.

Dr. Stout 27:07
And again. And they had a mental map of how I would react. And they had a plan and they they they'd set themselves up along the path because they knew I was going to be there. And they, they, I, they, I fell into every one of their traps.

Eric 27:20
That sounds like our friend's story from the Diamond district.

Dr. Stout 27:24
Yeah, well, yeah. No, I mean, this is. This is. This is how people are. We make predictions off of each other and and we are able to, I you know, exploit them. That can be for, you know, robbery purposes.

Eric 27:38
So so that's what the blue. J Blue. J Yeah. The blue Jay was trying to do to you.

Dr. Stout 27:44
It was predicting Me Yeah.

Eric 27:45
Right, Right. And this is exactly what the macaques were doing.

Dr. Stout 27:48 Yeah. Yeah. So.

Eric 27:49
So this happens across the animal kingdom at every level.

Dr. Stout 27:52
At every level. To the extent that things have brains, but things have more brains than you'd think that, you know, birds. You know, we think of bird brains, they're actually really smart. Basically things like jays and crows are quite intelligent. There's crows out there that can make tools. They'll actually strip a stick and stick it into a hole and pull out a bug with it. And so, you know, these kinds of capabilities that we think of unique as uniquely ours are throughout the animal kingdom, but we definitely also do them better. And we like to think of the gap between ourselves and the animal kingdom being based on our mentality. What I'm trying to say is at least at the same level as we're that much better than them on our thoughts, we're that much more advanced on our bipedalism. Our ability to go long distances is as unique a human adaptation as our advanced consciousness is. It's something that other animals do. We have just specialized on it and so we shouldn't think of ourselves.

Eric 28:55
Going, I'm sorry, we shouldn't think we.

Dr. Stout 28:56
Shouldn't think of ourselves as specialists in, you know, forming cities. We should think of ourselves very much as specialists in being super poor and maximizing resources and then working together and against each other to get those resources that are our societies are what keep us alive. But society preying on other members of society is built in from the very beginning with everything from robbery to prostitution.

Eric 29:27
So so the unique, the unique things about us at this stage are the the, the walking long distances, the endurance, the walking and the.

Dr. Stout 29:39
That's pretty much it. I mean, I love.

Eric 29:40
There's no other quality.

Dr. Stout 29:42
Not tremendously unique. We just have big teeth for grinding. Our teeth are larger than any other primates at this time and we can walk really long distances. Our brains are ever so slightly larger, but we're following the same.

Eric 29:56
You say it's the walking and the thinking.

Dr. Stout 29:58
That's the beginning of thinking. So chimpanzees are remarkably intelligent animals already, right? So they're they're they're they're they're far, far advanced of of of of the monkeys which are advanced of, say, you know, your dog or your cat. So we're already well along the path towards intelligence, but mostly for social reasons at this point. Okay. And you don't need that big a brain because the monkeys can already do a pretty good job of it. Okay. So we now we've grown our brain a little bit because you're never going to spend calories on something you don't need, especially in this environment. Right. You're not going to have extra.

Eric 30:33
But we need a little more because our environment.

Dr. Stout 30:34
Changed, our environment got a little harder and so our brain gets a little bit bigger. And so most of what our brain is probably doing is social interaction and the mental map of where we are. So understanding in time and space where the resources are and then understanding what it what it would take to get other members of our troop to help us out, give us food when we need food, help us when we're sick, you know, bring food to us if we need it, bring food to our babies if we need it. And I basically keeping the whole the whole system going needed just a little bit extra. And so that little bit extra brain is not a tremendous cost, but it's going to be something that we're spending calories on. And so given that we're specialists in not using up calories, it's a big deal that we've now grown our brain a little bit bigger. But seriously, what we spent our entire time doing would be chewing and walking.

Can you chew gum and walk at the same time? We're literally evolved to do that.

Eric 31:37
Which explains my kids love of gum.

Dr. Stout 31:40
Yeah, exactly. No, we are literally evolved to do that. We should have much harder gum. We should be chewing much more, much more difficult foods. Yes, it will wear down our teeth, but our teeth are pretty tough and it will give us much better jaw muscles. I actually have some interesting theories on orthodontia that a lot of orthodontia is is because we don't we don't chew enough, which doesn't create enough jaw space for our teeth to come in properly. That, you know, if you think about hunter gatherers, they didn't ever have dentists and they somehow got through their wisdom teeth erupting, erupting at the age of 20 without dying. Okay. So, you know, if they hadn't had room for their wisdom teeth, they all would have died. Interesting. And so we must have had larger jaws and we definitely had larger teeth. So we even had larger jaws. And that would have been the only way right up until we became farmers. So we had much larger jaws, too, about 10,000 years ago. And we can see this in Aboriginal groups, particularly in Australia today. They have the largest teeth and jaws of any other group.

Eric 32:48
So we've so we've been talking about millions of years ago. So so what, what, what makes this transition from two to, you know, the more contemporary

farmers from the, from the oh.

Dr. Stout 33:05
We're still not up to farming, we're not doing where we are, we're not going.

Eric 33:09
Yeah, future talk.

Dr. Stout 33:11
Farming is where everything goes wrong.

That's when we become lazy and get cavities and and it all goes wrong. And we do still exercise, but we exercise badly and we get bad.

Eric 33:22
That's such a better way to live.

Dr. Stout 33:24
It does in less. You think of the hunter gatherer life. It's actually

incredibly perfect. It's what we evolved for. So what we're and.

Eric 33:36
What we're still evolved for even now.

Dr. Stout 33:37
Even now, Yeah. So we evolved that millions of years of evolution to be a hunter gatherer involves very little work every day. They actually can get most of their calories without working as long as a farmer does. It involves a lot of walking. But if you don't mind walking, that's not so bad.

Eric 33:55 And I've.

Dr. Stout 33:56
Walked. So it's a lot of walking at this point. It would have been some digging later on. Our evolution would be some hunting, but not, you know, not more than a couple of hours a day most. And then the rest.

Eric 34:08
Where we digging with our hands or were we digging with.

Dr. Stout 34:10
Tools, we would assume.

Eric 34:12
That would make a difference, that.

Dr. Stout 34:13
The Australopithecines would have been able to have a stick. We don't know because Styx wouldn't have survived. But We know that chimpanzees certainly use simple tools like a stick or a rock to dig. So I would assume that that they would have done that with a stick or a rock. We didn't actually end up with fingers well adapted to digging. And for this first 4 million years, our fingers actually were long and thin still, which were very good for climbing trees, not good for holding things, even even even that. Stick for digging or a rock for digging. We could hold it, but it would have been

a very a poor grip, just sort of fingers on to palm, not a finger thumb grip. And so we could hold things. Certainly. Certainly chimps can. But these were fingers that were evolved, for one, from trees climbing up a tree very quickly. And we think they spent a lot of time in trees. So, for example, Lucy, one of the very early australopithecine fossils that was found we think fell out of a tree. And so she has broken femur and pelvis that indicates she fell like, you know, 40 feet out of a tree and then fell immediately into a water where she happened to be preserved. And you know that that's how we have her fossil. And there's not a lot of fossils because not everyone falls out of a tree into water immediately.

Eric 35:27
But it fell out of a tree and rolled right into water.

Dr. Stout 35:30
Pretty much, yeah. Within Within, you know, a day or two of of having fallen out of the tree was in water and then covered. So maybe a flood came and put sediments over her before the, you know, again Serengeti full of scavengers. So along comes the scavenger cracks all the bones. Yeah. Yeah. She had to and covered over pretty quickly. But the point is that we were still very much needing trees. So this was a an area where, yes, it's Serengeti, but there's these patches of trees within the Serengeti. And so we started off as a jungle creature living in trees and then were walking from patch of tree to patch of tree to patch of tree. But each patch of trees only has a certain amount of resources. So we maximize the resources we get out of that patch of trees, store as much of it that we can as fat, and then we walk to the next next patch of trees and we sleep in the trees during the day and we come out and we dig around them. The trees are almost always near water, so there's a lot of water nearby. Now it's interesting, if you think about

chimpanzees and gorillas compared to monkeys, they actually have less fur on them than monkeys. And so one of the other things you might notice about humans is we're slightly less furry than the monkeys are. And so this is probably happening during the same period of time where we're moving out onto the grassland. And so in general, there's a correlation with the larger the primate is, the less fur it has. And this would have set us up nicely. For whatever

reason, almost none of the other primates sweat. It doesn't make a lot of sense to sweat in a rainforest is almost 100% humidity, so you don't get any evaporative cooling, right? So we move out onto the Serengeti as these furry, non sweating apes, and we're getting hot really quickly and we're being eaten all the time. So we have to figure out a way to divide our habitat into a way that avoids predators and allows us to walk from place to place and scavenge food without getting eaten by all the time. So all of the predators on the Serengeti are most active during the morning and the evening and sometimes at night. So we climb into the trees at night to avoid that whole period. And then we get up and we move around during the middle of the day when it's super hot, hottest.

Eric 37:38
Part of the day when the other animals don't want to move.

Dr. Stout 37:40
Around. And so what we evolved the ability to do is to sweat off of a naked skin. So we lost our fur and we sweat and that evaporative cools us and we need a lot of water.

Eric 37:50
LONG Does a transition like that take that sounds like that would take a very long time.

Dr. Stout 37:55
All of these things were selected for very highly. That's why I said we don't have a lot of intermediary fossils.

Eric 38:01
So these so the things that did not they would have died very quick.

Dr. Stout 38:06
Right. And we don't have any fossils of sweat glands or hair, so we really don't know. But what you see is a very quick transition to being a biped, you know, So if you think of a a of a dog skull, it is a hole at the back of the skull, the form of Magnum where the where the spinal cord attaches at the back of the skull. If you think of a human skull, it has a hole at the bottom of the skull to hold the skull on so that you can look forward and look instead of looking straight up. Right. So that happened very, very quickly. As we move to being bipeds, the central form in Magnum appears very early in the fossils. A couple other things. If you look at a chimpanzee's pelvis, it has these two long things in the back to sort of hold the lower back while you're bent over, not walking on your knuckles. If you look at a human's pelvis, it looks like a bowl. So so that's for a vertical oriented organism with a cup shaped or bowl shaped pelvis to hold your internal organs in place as you're walking around. That also occurs fairly quickly. So these these adaptations where you couldn't survive without it happened very quickly, you know, quickly could easily be half a million years or a million years. And they just we don't have any fossils from that intermediary one. We have a lot of fossils that are part way.

Eric 39:23
They're an evolutionary quick movement is something that could take between a half a million. Well, this.

Dr. Stout 39:29
Was a brand new ecosystem. This was this was as large an adaptation as birds getting wings right. So I a a African ape moving on to a grassland. Apes have never been on a grassland before. We're the first ones to figure it out. It was by necessity. Our jungle dried out and it's a whole new

ecosystem niche that we can now exploit. And so it's you get what's called I i, i radiation and speciation into all the different possible habitats. So some of these are better walkers than others. Some of them have longer legs, some of them have shorter legs, some of them have stronger bones. They maybe did more digging, others have even jaws. They all have large jaws, but some of them have really, really large jaws. And they could have been chewing on ones that the other, you know, more grass while i australopithecines would not have been able to chew. So the groups are radiating into many different species. So it's not a straight sort of line between chimpanzees and us, but it's a very bushy family tree.

Eric 40:42
And nonetheless, all of them had the ability to adapt or they would have just died.

Dr. Stout 40:47
Well, yeah, I mean, every everything is always adapted to whatever it happens to be. And it's just that this is a very new environment. And so the adaptations are very happening very rapidly at this point.

Eric 40:58
And with great variety. Yeah.

Dr. Stout 40:59
And it turns out there's also a lot of just

I it doesn't always have to be evolutionary adaptation. That's what we're talking about. But the body can adapt to a new environment on its own. So there's a strain or an ostrich. There is a practice in Japan where they force macaques to walk on two legs and act in plays as a samurai monkey.

Eric 41:30
That doesn't sound right.

Dr. Stout 41:32
And they, they, they, they force slash encourage them to walk up to two kilometers a day, like holding their hands as they walk along up and down the street. And these macaques actually develop many of the adaptations you would expect in a biped because they're forced to become bipeds.

Eric 41:49
They develop them in an individual.

Dr. Stout 41:51
In an individual. So obviously you don't see the skeletal adaptations that you would expect to see in a biped in terms of the way the, you know, the hip sockets are going to be going in.

Eric 42:02 Evolutionary change.

Dr. Stout 42:03
Or the way, you know, when we walk, our knees are directly under us. They're not on either side. When a chimpanzee walks, its knees are under its hips, and so it tends to go from side to side, whereas humans can walk straight forward. These macaques don't get knees directly under them because that's just a thing they they don't have. They haven't evolved that far, but they are able to walk as bipeds for for, you know, over a mile every day and they're able to stand on stage and do their their scenes very well. So, yeah, you could imagine that, you know,

a chimpanzee can take a couple of steps as a as a biped. They're not very good at it. What kind of adaptation would that give you right away? Your inner grassland. You need to get to the next patch. Simply standing on two legs gets you above the grass. Right? So now you can see if there's anything else out there and you can see where the next tree is. And so then you go back down to all fours, but now you're lost, so you spend more and more time being upright. Now, I'm not saying that this is Lamarckian evolution where one chimpanzee passed down acquired characteristics for the next generation, but there is an advantage right away to having some of these primitive patients do.

Eric 43:15
That instantly, have a disadvantage.

Dr. Stout 43:17
Instantly have a disadvantage. And so it was selected for very, very quickly. And so you see adaptations going in a bunch of different directions, but all of them allowing for these longer distances.

Yeah. So I want to I want to continue on with these discussions, sort of move us through evolution until we get to talking about these evolutionary history in relation to, you know, our modern existence. But we're still we're still we haven't even gotten big brains yet. So next time what I'd like to do is start talking about how we got these larger brains beginning of genus homo moving from the Australopithecines, which were our first 4 million years of evolution, basically bipedal chimpanzees to now the next 2 million years up till now, where we have large brains and we have the capabilities of of a large brain hunter out on the Serengeti, which changes everything. You know, being a occasional scavenger and a digger of tubers is quite different from what what our genus then evolves into, which is is is hunters with tools and fire and a and a whole new class of living. So just like you have adaptive radiation with the the, the bipeds moving out of the Serengeti are becoming a large brained tool user is another kind of ecological niche that we are then able to exploit and gives us entire new set of capabilities. And so that's what I'd like to talk about next time.

Eric 44:54
I'm actually excited. Excellent. Excellent. All right. Thanks.

Dr. Stout 44:58 Thank you.

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