The Birth of Homo Sapiens

Human evolution is frequently featured on television. Ever since Darwin realized that humans have biological origins, the question of what our ancestors were like in an anthropological sense has been a constant focus of social interest.

Regarding the process leading to Homo sapiens, there used to be classifications like 'ape-men,' 'primitive men,' 'ancient men,' and 'modern men,' but these are no longer considered correct classifications and are basically not used in academic circles. However, they are still used as convenient terms in Japan.

This doesn't mean pointing to a specific single species; rather, they are used as terms to represent certain stages—for example, calling the oldest period of humanity 'ape-men'—and in that sense, I think they are still effective today.

Looking back from the present, we can set certain stages, but it feels more like saying 'there were these steps to reach Sapiens.'

While it's easy to understand, I feel there's a part of it that could be misinterpreted as suggesting that we, modern humans, are the pinnacle of evolution.

Nowadays, even on TV, people often say that the process of evolution wasn't a straight line. That's true, but saying 'there were many types of humans and only Homo sapiens survived' is a bit misleading.

There is much debate about whether there were actually many different species. Even if there were, the specific ancestors are the intermediate stages. So even if you say only Homo sapiens survived, they couldn't exist without those who came before. When people say 'there were 20 species and only one survived,' I feel like saying, 'Wait a minute.'

It's not like they evolved gradually from ape-men to primitive men, ancient men, and then modern men; there were times when they coexisted.

Exactly. Conversely, I'm not sure about over-emphasizing that a huge number of species coexisted either.

It seems the points people want to emphasize change depending on the time.

Increasing the number of species makes for a more interesting topic, so I think the 'splitters' (those who favor more species) are currently doing a good job of capturing public interest (laughs).

My specialty is mechanical engineering, but when I look at humans as machines, I think they are amazing. While it's difficult to realize a machine like a human, I feel that challenging that is important for mechanical engineering, which is why I work in the field of anthropology.

When you think about it deeply, humans are ultimately products of evolution. I think it's incredibly important and interesting to consider the mechanisms of human movement from that perspective.

From a mechanical engineering standpoint, is bipedalism the interesting part?

Yes. It's generally recognized that the definition of humanity is the start of bipedalism.

That's not necessarily the case. You can define it that way, but the current interpretation is to first say 'the origin of humans is where we branched off from chimpanzees' and then 'bipedalism happened to start as a result.' There must be at least a few human ancestors who were not bipedal.

I suppose that's true, but then, how do you distinguish them?

That's another issue. Currently, we can't distinguish them.

Ultimately, it's a question of how we can recognize them. If old bones come out of Africa and it seems they were bipedal, people will say, 'That must be a human.'

Certainly, from a phylogenetic perspective, I think what Kono-san said is correct, but as a practical matter, I think 'being bipedal' ends up being used as the definition.

Conversely, for early humans, what kind of evidence could allow us to say 'this is a human' even if we don't know if they were bipedal?

The reduction of the canine teeth. Humans have small canines, and there is no difference between males and females. Chimpanzees and others have large canines with sexual dimorphism, but in humans, they gradually get smaller.

However, proving that is difficult. If you find one fossil and say 'it's small,' someone will just say 'it's probably a female' and that's the end of it.

You need to know the distribution to some extent.

Exactly. More than 20 canines of Ardipithecus ramidus (Ramidus ape-man) from 4.4 million years ago have been found, but not a single large one exists; they are all only about the size of a female's. Therefore, it is argued that the canines had already become small.

The probability of finding 20 and having them all be from only one side is infinitely close to zero, so that's the conclusion. But you can't say that until you find 20.

When you get down to it, anthropology is also a science of frequency. Ultimately, you examine how much the frequencies differ, and only when it's 'almost impossible' do you reach a conclusion.

However, in anthropology, there are many one-of-a-kind fossils, so often you can't say that. It's an endless effort to fill in the gaps by gradually discovering more and somehow reaching a valid scientific interpretation.

In a discipline based on fossils, it's natural for numbers to be small, so in a strict sense, it's difficult to say whether differences truly exist within a biological group with variation. So, we pile up evidence to make it as plausible as possible (laughs).

Even if you say 'plausible,' 'outlandish' theories are no good.

It means 'as correct as possible.' That's why theories are frequently rewritten. When a fossil that didn't exist before appears, the way of thinking changes. In that sense, I think it's dynamic and interesting.

Even within the same species, there are naturally individual differences. There's no criterion to judge whether two fossils are within the range of individual variation or are different species.

In old high school textbooks, primitive men were given different species names like Sinanthropus pekinensis (Peking Man) and Pithecanthropus erectus (Java Man). At some point, the conversation shifted toward unifying them as Homo erectus.

When fossils increase to a certain extent and comparisons show they aren't that different, a movement to lump species together sometimes occurs.

On the other hand, there's also a movement to separate African fossils that were lumped under Homo erectus because they are too different. So, it's a repeated cycle of lumping and splitting. Ultimately, how to divide them is something humans decide.

When speaking of humans before Sapiens, general people in Japan might first think of Peking Man. Neanderthals have a strong image of being European.

Neanderthals did reach as far as southern Siberia. In China and India, things categorized as 'ancient man' class have been found, but their relationship with Neanderthals isn't well understood.

Asia yields many fossils of primitive men (Homo erectus). There are ancient men, but not enough have been found to judge where they should be placed.

I'd like to ask Ogihara-san, are there striking mechanical differences between Peking Man or Neanderthals and modern humans?

It depends on what level you look at the differences, but from a macro perspective, I don't think they are dramatically different physically.

The differences between early humans like ape-men—and even before that, around when bipedalism started—are interesting, but from primitive men onwards, honestly, I don't think they change much.

What about things like the degree of muscle development?

I don't think it's that different. Even if there are individual differences, they probably fall within the scope of variation. Primitive men can do an overhand throw. In short, they are basically close to modern humans.

Could ape-men not do an overhand throw?

That's what is said. At least chimpanzees cannot do an overhand throw well.

They can't do a take-back like a baseball pitcher, can they?

Exactly. The structure of the shoulder and the shape of the scapula are quite different. The apes in 'Planet of the Apes' throw spears from above (laughs), but chimpanzees basically throw underhand. I believe it becomes possible from the level of primitive men.

Is there not much difference in walking itself between primitive men and Sapiens?

Yes. I don't think they can be considered different. The speed probably isn't that different either. There's a recent theory that humans are suited for long-distance running, and that is also said to start roughly from the level of primitive men.

That's Daniel Lieberman's theory mentioned in the NHK program 'The Birth of Mankind.'

Yes. From around the time of Homo erectus, they became able to track and kill prey over long distances. So the theory is that while humans are by no means sprinters, they are better suited for endurance than other animals.

That would mean the structure of the lower limbs became more like modern humans around the time they became primitive men. Honestly, it's difficult to distinguish whether they are better suited for running or walking.

There are stories that say every single part of the human foot is an 'adaptation for running,' but I'm not so sure about that.

There was also the story that because they lost their hair and could sweat, heat didn't build up, so they wouldn't get heatstroke even if they kept running long distances.

How do they know they didn't have hair?

That's just an assumption (laughs). There's no evidence anywhere.

If you use CG to recreate ancient humans in hairless and hairy versions, at a cognitive level, we feel the difference between 'human' and 'beast.' The impression is completely different.

But isn't the idea that by the time they were primitive men, sweat glands developed and hair was lost, allowing for efficient heat dissipation, considered a factor in adaptation for running?

But in the NHK program, Homo habilis (the earliest primitive man) was hairy.

I wonder if there's a line between Habilis and Erectus. Habilis are the people around the time they encountered the Monolith in '2001: A Space Odyssey.' That's based on an assumption of 3 million years ago.

Why was it decided that Habilis has hair?

It's probably because they want to make the story about Erectus running long distances, so that's when they first became hairless. I've watched the same program about six times for class, so it's ingrained in my head (laughs). There's no reason to deny that hair was lost earlier, and there's a possibility they still had hair at that point.

They probably made them hairless to fit the background that by the time of Erectus, they were living completely on the ground and out in the savanna.

It's an analogy that they must have sweated at least a little to survive.

Can we tell if they had hair or not through DNA? It seems there are many things we've come to understand through DNA.

Erectus is likely too old for DNA analysis.

Phylogenetic relationships have become very clear. In other words, we know which species are more closely related to each other.

We can also tell in what order they branched off, right?

Basically, with fossils, we talk about morphological similarity, but when we examine DNA, we often find that even if the shapes are similar, they were actually different.

For things that can only be identified by fossils, there's nothing we can do. If it's as recent as Neanderthals, we can extract DNA. Even though they are called fossils, the bones haven't turned into stone yet. But before that, they are stone, so we probably can't get DNA.

The oldest DNA extracted so far is from Homo heidelbergensis, dating back 400,000 years.

In the past, there was the multiregional evolution hypothesis for Sapiens, but now the Recent African Origin hypothesis is well-established.

Basically, yes.

That's exactly what we've learned through DNA.

Homo erectus is also considered to have originated in Africa.

Are Neanderthals perhaps the only ones that might have originated outside of Africa?

Even so, the ancestral species of Neanderthals was Heidelbergensis, and if you trace back further, the image is that they ultimately came out of Africa.

Yes, I think it ultimately comes down to an African origin.

The Recent African Origin hypothesis refers to the origin of Sapiens, but it's striking that other hominids and close relatives of humans also trace back to Africa.

But even if we go back to the great apes, do they also originate in Africa?

It is believed that all great apes, if you trace them back, originated in Africa.

Is that so? Mr. Ogihara, you are researching Nakalipithecus, a 10-million-year-old fossil ape found by Kyoto University in Kenya, right?

Unfortunately, I'm not directly involved with that one. What was found was a jaw (laughs).

Kyoto University discovered a 15-million-year-old fossil ape called Nacholapithecus, and for that one, they found almost the entire skeleton. However, fossils from the period close to the divergence between humans and apes are mostly teeth and jaws. It's difficult to estimate locomotion patterns from just a jaw.

Regarding teeth, various specimens have been found from about 30 million years ago for apes up to just before humans, though they are sporadic. However, it's not clear which ones are in the direct ancestral line of humans.

Early apes had simple teeth, but later the enamel became a bit thicker and more ape-like; that's about the only difference.

What are the points that make you think, "This is an ape"?

It's the shape of the teeth. If you look at the teeth, you can tell it's an ape.

So early apes had ape-like teeth, but their bodies were basically monkey-like.

By the time of Proconsul (an extinct fossil primate) 25 million years ago, quite a few body bones have been found. We call them "dental apes" because if you go back that far, the teeth are ape-like, but you can't tell from looking at the body.

Basically, they were monkeys that walked on all fours in the trees.

We assume the reason the tooth shape evolved and the enamel thickness changed was due to food. However, recently the tone of the debate has shifted toward the idea that enamel thickness changes more easily through evolution than previously thought, making it impossible to judge whether something is human based on that alone.

I've visited many sites where Asian hominids were excavated, and Homo floresiensis is fascinating. There's a reconstruction model at the National Museum of Nature and Science, but everyone was shocked when the paper was published in Nature in 2004. They were only 110 centimeters tall.

That was a real surprise.

When you actually interact with a 110-centimeter child, they are surprisingly small. Even some kindergarteners are over 110 centimeters.

One wonders if a hominid could really become that small.

And the brain was also very small.

On par with a chimpanzee?

Yes. And yet they were as recent as tens of thousands of years ago; it's baffling. The theory that human brains have consistently grown larger turned out not to be universally true. Other hominids were all around 160 centimeters, right?

At the museum, there's a 1.5-million-year-old African hominid boy called Turkana Boy, and even though he's a boy, he's about 165 centimeters. Even for Java Man, it's said that based on the femur, there were individuals over 170 centimeters.

Hominids are large, aren't they? Why did Homo floresiensis become so small? They must have been large at first and then shrunk.

It's thought that they crossed over to the island and became smaller there.

Does that mean they adapted?

That's right. In an island environment, there are no predators and food is limited, so there's no need or opportunity to grow large, and they gradually shrink. There's a phenomenon called insular dwarfism, and it's said this might be a dwarfed version of humans.

But some people aren't convinced. They say, "Humans don't get smaller. Brains don't get smaller" (laughs).

There are people who insist it's a diseased Homo sapiens, and various other theories.

Since Java Man was likely nearby, the most straightforward interpretation is that they went there and became smaller.

But even though they were so small, their stone tool techniques weren't primitive, were they?

Exactly.

Maybe brain size isn't actually necessary? (laughs)

Maybe the cells themselves became smaller? With the number of cells remaining the same.

But doesn't cell size not vary that much between species?

That's true (laughs). Whales, elephants, and mice are all the same.

It's purely mysterious.

For 40 or 50 years, only stone tools were found, and then the bones were discovered. At first, even though stone tools were appearing, many people didn't take it seriously.

Yousuke Kaifu, who is now on the research team looking at the bones, said, "Even when they said fossils were found, I didn't take it seriously at first" (laughs).

In Southeast Asia, on islands like Sulawesi and Luzon, there are places where only stone tools have been found and the bones of the makers haven't appeared yet. Chronologically, they should be close to the era of Homo floresiensis, so it's interesting to see what kind of bones will turn up.

The first major turning point was when early humans eventually began walking on two legs and their canines became smaller. The next major turning point was when the brains of the genus Homo began to grow larger somewhere between 3 and 2 million years ago.

We call those with large brains the genus Homo. It's said the brain grew larger because they started eating meat. But this is also a circular argument. They could eat meat because they used tools, which made the brain larger, but why could they make tools? Because the brain was large. It's a cycle.

However, as with Homo floresiensis mentioned earlier, there are cases where they used tools even with small brains.

But they are still genus Homo. The definition has broken down, but we can't call them anything else.

I suppose so.

You can't really split them up that much at the genus level. From a cladistic perspective, if you split that one off, you'd have to dismantle everything else.

In any case, those two phases are where the major changes occurred. However, it's not yet clear whether it progressed at a steady pace or changed rapidly at some point.

Regarding the brain, we know to some extent at what pace it grew; NHK said it grew significantly once they became Erectus.

NHK works very hard to create proper programs. That's for sure, but they aren't necessarily correct about everything. I hope you can view it as one way of capturing the current theories in the world.

The general public tends to think that a standard interpretation has been decided, but that's certainly not the case.

It is often called the "replacement" of Neanderthals by Homo sapiens, but how should we interpret this? A while ago, it was frequently expressed using the word "replacement," but recent DNA research has provided one piece of evidence after another supporting interbreeding, so I feel a sense of discomfort with the word replacement.

Also, regarding archaeological evidence, it used to be said that relatively advanced abstract expressions and artifacts related to art did not appear until Homo sapiens, but recently there have been more stories about evidence being found that shows Neanderthals also had such abilities.

In the past, there were often people who wanted to say something dramatic, like there was a war and the Neanderthals lost.

That's true. I don't hear that much lately, though. To be honest, I don't know what the most plausible hypothesis is.

The sizes of Neanderthals and Homo sapiens are almost the same. Anatomically, they are almost identical, but the shape of the head is different.

Since their bodies were slightly larger, the general consensus is that the absolute size of the Neanderthal brain was also slightly larger. However, I think Sapiens might have had a relatively larger cerebellum. As for where Neanderthals were larger, it was the occipital lobe, the area at the back of the head that primarily governs vision. However, it is also true that these are subtle differences.

Thinking simply, is it possible that Neanderthals lived a more visually dominant lifestyle?

Papers have been published suggesting that because Neanderthals lived at relatively high latitudes, it might be because they lived in dark environments. But we don't know for sure.

It is probably true that the cerebellum of Homo sapiens is large, but it's debatable whether there is a meaningful difference there. So, if asked whether the difference in brain shape was a factor in the replacement drama, I can't say anything definitive.

I think having a large occipital lobe or a large frontal lobe would be directly reflected in the shape of the skull, but is it reflected even when it's something small like the cerebellum?

It is reflected. The shape around the lower part of the back of the head is smaller. We performed a task where we tried to deform a human brain to fit it into a Neanderthal head.

When we calculated the mathematical deformation to fit the human brain in, we noticed that the fit around the cerebellum was poor. At first, we were working under the preconception that differences would appear in the frontal lobe or areas related to higher-order functions, but in fact, the area with the most different shape was the lower part of the back of the head.

So the frontal lobe didn't change that much.

As a result, yes. Looking at the head as a whole, the shape around the forehead is quite different between Neanderthals and modern humans. Because of that, I thought the area around the frontal lobe might be different, but when we compared the shape of the cranial cavity, there wasn't much difference.

The largest Neanderthal head was found by a team from the University of Tokyo, wasn't it?

That's right. It was discovered in a cave in Israel. It's 1740cc. It's extremely large, but that individual was also tall. Generally, Neanderthals are said to be larger and more thick-boned.

Since the cerebellum is small, and the cerebellum is an area closely related to motor skills, one might think their motor skills were low, but we don't think so. The cerebellum has many connections with the cerebrum and is also related to higher-order functions, so we believe it led to differences in cognitive function rather than motor nerves.

It is said that Neanderthal teeth have thinner enamel for unknown reasons. But it might have just happened to shift in that direction.

There is a story that Neanderthals had heavy wear on their front teeth. It's also said they might have used their front teeth to tan hides.

Modern humans also vary by era and region. As times become more recent, for example, if a division of labor occurs within the same group, it can happen that one person's teeth are worn down while another's are not.

What DNA is most different between Neanderthals and Sapiens?

I believe there was a story that genes related to language and brain development are slightly different.

Their skin color was light, wasn't it?

Yes. It is said that interbreeding occurred several times.

Can we estimate how many times?

To be honest, I don't know very well.

I want you to tell me (laughs). But there seems to be evidence that interbreeding occurred.

Also, regarding Denisovans, they were contemporaries of Neanderthals, and only a pinky bone and two teeth have been found, but when DNA was taken from them, it turned out there was another species that was different from both Neanderthals and Sapiens.

I hear that people researching DNA are saying various things, like people around Melanesia have inherited genetic material from Denisovans, or that the high-altitude adaptation genes of Tibetans come from Denisovans.

It's becoming a surprisingly big story.

Yes. And the locations are spreading all over the world.

Well, it's a fact that Neanderthals and Homo sapiens coexisted during the same period. Whether it was all at once or gradually, we don't know, but Neanderthals disappeared.

They overlapped for tens of thousands of years, which is long if you call it long. Homo sapiens was born in Africa about 200,000 years ago, but it's said they didn't fully leave Africa until 60,000 or 70,000 years ago. If they coexisted after that, it was during the period until Neanderthals were gone by 30,000 or 40,000 years ago.

Looking at the results, Homo sapiens survived, but many people see the title of the book I wrote recently, "Why Are We the Only Ones?" and think the answer is written there (laughs).

I intended it as a way to set the question. For example, there are many possible explanations for why I am in this meeting room right now. It's probably impossible to narrow it down to one. There must be an element of chance as well.

I suppose you could say that humanity, which had been diverse until then, became a single species after the Neanderthals were gone. Consequently, you can also say that movement was active. Because they advanced into places where previous humans had not gone.

Without geographical isolation, they become a single species. If one reason they became a single species is that the population exploded and spread throughout the world, then why did the population explode like this?

Perhaps, rather than a romantic story like "they could go anywhere," it might be that the population growth became so significant that they had no choice but to leave.

In the first place, when it comes to why the population growth occurred, I think it might stem from cooperation or social intelligence. I don't think things like agriculture could be done unless there was a foundation of getting along well with others.

Agriculture didn't start until about 10,000 years ago, but they had already reached Patagonia during the hunter-gatherer era.

I think there was some kind of cooperative behavior, and that contributed to increasing the survival rate.

So, if the story becomes that cooperative play was necessary to hunt mammoths, for example, would that be too easy to understand? (laughs). Like that being related to the cerebellum. One can imagine many things.

Since the time of Erectus, hunting by endurance running probably linked to doing things in groups, so you could also think that the brain enlargement from that time is related.

In that case, Homo floresiensis is even more of a mystery.

It is said that Homo sapiens arrived in the Japanese archipelago about 38,000 years ago. Unfortunately, no evidence of people from earlier stages, such as Peking Man on the continent next door, has been found to this day.

Sites where stone tools and such are found begin to appear nationwide from about 38,000 years ago. However, almost no bones are found. Bones are difficult to preserve in the Japanese archipelago due to the soil conditions.

The exception is Okinawa. Since Okinawa is limestone land, bones are easy to preserve. Paleolithic bones have been found in about 10 locations in Okinawa and only one location on Honshu.

Where is the one on Honshu?

It's the Hamakita site in Shizuoka. It used to be said there were more, but when the dates were examined, they turned out to be newer, or they were judged not to be human bones.

In Japan, archaeology and anthropology are separate disciplines, but in fact, when learning about humans from ancient times, people in other countries often work together. For example, if you want to know about Neanderthals, you need both an archaeological approach and an approach from bone morphology.

In Japan, from the moment you enter university, they are split cleanly, and I think it's unhealthy that there isn't much interaction and they are thought of as separate disciplines. Mr. Kono, do you feel a gap in that regard?

It's true that there is a distance from archaeology. However, more than that, the anthropology industry has shrunk, and jobs and posts are decreasing. In the past, quite a few anthropology professors belonged to the Department of Anatomy in the School of Medicine, but now there are fewer. To begin with, there aren't that many universities that can train students.

On the other hand, when bones appear or when there's a special feature on an NHK program, everyone is happy to watch (laughs).

Mr. Kono, your current affiliation is the Faculty of Letters, isn't it? Anthropology within a Faculty of Letters is relatively rare.

But anthropology is a field of science, and while it's not immediately useful, it deals with the essence of what a human being is, so it connects somewhere to what people in the Faculty of Letters do.

At first, I wondered why I was talking about this to students in the Faculty of Letters, but when I have them write their impressions, they write things like, "I thought it was important for humans to use tools and have culture, but I was surprised to feel that the body structure is the same as other primates," so I thought, "I'm glad I did it."

I think it's good that people who will think about humans in the future will also look at humans from a biological perspective. Occasionally, there are students who want to research bones.

Professor Ogihara, are there any students in your department who are interested in anthropology?

Basically, there aren't many, but the discipline that the study of the evolution of human bipedalism is based on overlaps considerably with things like robotics.

Originally, I think there is a foundation where if robotics were also done with people who have a biological perspective, something a little different would be created.

I think it's a field that the general public is also interested in, so I hope the number of students interested in anthropology increases.