Anthropologists Have A Bone To Pick With New Skull Finding

A reconstruction of an ancient skull suggests that humans could have evolved half a million years earlier than thought. Not so fast, some say.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Ira Flatow?

  Science Friday is supported by MathWorks, creator of MATLAB and Simulink software for technical computing and model-based design. MathWorks, accelerating the pace of discovery in engineering and science. Learn more at mathworks.com.

• 0:17Flora Lichtman?

  Hey, this is Flora Lixman, and you're listening to Science Friday.

• 0:23Flora Lichtman?

  Today in the show, new skull just dropped. An ancient hominid fossil from China is shaking up the human origins field.

• 0:31Speaker 02

  This is really a case where if you have another piece of evidence, it might be a good time to sort of show people.

• 0:43Flora Lichtman?

  A new analysis of a very old skull challenges what we thought we knew about our ancestral family tree and its timeline, at least according to the researchers who wrote the paper. The study in the journal Science claims that Homo sapiens and some of our relatives could have emerged at least a half a million years earlier than we thought. But as we know, big claims require big evidence. So here to piece together the details is Dr. John Hawks, an anthropologist and professor at the University of Wisconsin Madison. He studies the bones and genes of ancient humans. John, welcome back to Science Friday.

• 1:17Speaker 02

  Hey, thanks for having me.

• 1:19Flora Lichtman?

  First of all, is it drama in your field right now?

• 1:22Speaker 02

  You know, look, I'm a field that's got a lot of drama in it, but I will say that this is a really astounding claim and one that has drawn a lot of attention to the question of whether we know as much as we thought we did about our recent past.

• 1:39Flora Lichtman?

  Okay, let's talk about the study. I know it centers on this very crushed up skull. Tell us about it.

• 1:46Speaker 02

  Yes, so this site in central China, widely known as the Yunshan Site, is a site where in 1982, partial skulls were found, and they were both highly crushed. That makes them tough for us to study, obviously, but they have features that connect them with an early species in our ancestry known as Homo erectus. The new study has created a reconstruction of one of those skulls that tries to put it back into its anatomical order so that we can see more about its anatomy and therefore its relationships with us and with other hominids. And their claim is that this is actually not a Homo erectus. It's actually something that's closer related to us and related to some more recent skulls

• 2:31Speaker 02

  from China, skulls that in recent years have been called Homo longi. And so the idea is that this lineage of hominins is something that evolved in China, maybe before a million years ago, and existed much later than that in China until at least 200,000 years ago or later. The interesting piece of that is that this lineage, we have DNA from the most recent part of the lineage. And that DNA connects them with a group that we know as the Denisovans, a group that is really important in our ancestry because they are among the ancestors of today's people.

• 3:09Flora Lichtman?

  So was there DNA from this skull?

• 3:13Speaker 02

  No, there's no DNA from this skull from Yunshan. And in fact, at around a million years old, it's a, you know, it's very much a long shot that there would be DNA evidence from this very ancient time.

• 3:27Flora Lichtman?

  Is the main takeaway here that this skull looks different and actually more modern than we thought it should?

• 3:37Speaker 02

  Yeah, the story of the research is that this skull is more advanced than we thought it should look at a million years ago. It has a larger brain, it has a more rounded skull, it resembles some of the later skulls. And so the idea is that maybe this more modern form had already appeared before a million years ago. You know, where, where the interest is for anthropologists like me is that we have a genetic timeline. We've got DNA from some ancient fossils. Those include the Denisovans and the Neanderthals. And those are all later fossils. Those are all fossils that existed within the last 150 to 200,000 years that we have DNA. But we can use that DNA to reconstruct their tree.

• 4:23Speaker 02

  The tree of relationships of those lineages, the Neanderthals largely in Western Eurasia, the Denisovans largely in Eastern Eurasia, and African ancestors of ours, modern humans in Africa, those branches, we estimate from DNA, go back around 750,000 years ago. So a skull like this, if it belonged to the Denisovan branch, would suggest that our timeline was wrong, that maybe the DNA is giving us the wrong picture about how long ago our ancestors arose. And that throws into question a lot of things that we estimate from DNA.

• 5:01Flora Lichtman?

  I'm gonna take a wild guess that not everybody in the anthropology world is on board with these conclusions.

• 5:10Speaker 02

  Yeah, somebody like me, I study DNA and I study ancient fossils. And I've got to tell you that ancient fossils can look similar for lots of reasons. Their environments could be similar. They have similar adaptations because natural selection has affected their populations. DNA has got 3 billion base pairs of genome that we can compare between different individuals and different populations. And that's a lot of information. We have a lot of knowledge today about the tree of these populations from DNA. And so it would take a really, really convincing set of evidence for me to go and say, you know what, I think that Denisovan DNA, we got it wrong. I just, I'm not there with this evidence.

• 5:57Flora Lichtman?

  What would be a convincing amount of evidence? Like another skull?

• 6:03Speaker 02

  You know, the really interesting thing about this site is that there is a third skull that was discovered a few years ago and is still in the process of being studied. We know that it's there, but we can't see it yet. And the folks who are working on it, I'm sure they're doing great work on it. But this is really a case where if you have another piece of evidence, it might be a good time to sort of show people, hey, we've got more than just this skull that we rebuilt. We actually have a set of evidence that is making us, it's reinforcing our new point of view.

• 6:38Flora Lichtman?

  Our anthropologists like, release that skull.

• 6:43Speaker 02

  You know, that's sort of my attitude. I always feel like our, our conclusions are the strongest when we can share the data with everybody. And in a lot of cases, we're not there, you know, countries have different models of how people work on their fossil remains. They don't release things as openly. And, and I am always advocating for a vastly more open release of things. If we can see the stuff, we're in the United States and in many other parts of the world are facing a lot of doubt about evolutionary science. And one reason for that is that the evidence isn't just there for everybody to see.

• 7:18Flora Lichtman?

  I want you to put this finding in context. I mean, it seems to me, just from covering this, that the ancient human family tree has been in major flux, you know, for the last decade or two. New branches, new intersections. Can you give me the sort of 10,000 foot view of the field?

• 7:40Speaker 02

  Absolutely. Over the last 15 years, we've acquired this ancient DNA record of the later parts of our evolution. And throughout the earlier parts, going back to as early as seven million years, we've found new fossils that give light to new branches that we didn't suspect had existed. We have unexpected branches in South Africa, the species that I was involved in helping discover Homo naledi, that is really different from today's people, but existed until 250,000 years ago or less. So it existed when our species arose. The Neanderthals and Denisovans, we now know, contributed DNA to our lineage, to our line,

• 8:22Speaker 02

  modern humans. And that suggests a network of connections. So we're looking at a tangled web of relationships going back in time with some new members of our family that we didn't suspect had existed, but also new connections between some of the old ones.

• 8:38Flora Lichtman?

  I mean, this must be vastly different from when you began working in this field.

• 8:44Speaker 02

  You know, when I first started, we were still arguing about whether there had been ever more than one kind of human ancestor at a time, or whether the tree was filled out with more branches. And today, we're looking at dozens of branches, some of which reconnect over time and become part of our ancestry in different ways, and some of which go off in very different directions. We have a fossil diversity in our ancestry that nobody appreciated 30 or 40 years ago.

• 9:18Flora Lichtman?

  You know, whenever we see headlines like this, you know, that the skull pushes back the timeline of human evolution, or changes some relationship between ancient humans, you know, I, I think it raises the question of why, you know, why should we care about that? If something did evolve a couple hundred thousand years earlier than we thought, why is that a big deal?

• 9:42Speaker 02

  You know, I think that my answer to most people about that is that when you look around the world today, there's this tremendous diversity of people that you see, right? People are different colors, they look different, they're different sizes, their hair is different. And we think of that as being really different. The fact is that people around the world everywhere today are more genetically similar than chimpanzees that live in neighboring groups in one small part of the Democratic Republic of Congo.

• 10:12Flora Lichtman?

  Is that true?

• 10:13Speaker 02

  Yeah, absolutely. And so you have what is today so low variation genetically, but very high variation in some respects, right? You look at people, they look different. And that can be confusing, right? How does this emerge? It emerges because our lineage is adapting rapidly to new landscapes, new environments, using the genetic heritage that we all share in different combinations. Uncovering the ways that that has come to pass helps to inform us about our shared humanity, the fact that we're all the same everywhere, but also helps to inform us about our potential. As we move forward into the future, we're drawing

• 10:56Speaker 02

  upon our genetic variation that comes from such a limited number of ancestors in the past. And we're trying to learn how they lived so that we can think through how we can shift and change our lifestyles in the future.

• 11:10Flora Lichtman?

  Hmm. What, what do we need data wise to definitively answer some of these questions about our past, about timeline, about family tree?

• 11:19Speaker 02

  You know, fascinating, the fascinating thing is that, you know, today I can tell you the answer to questions that remained open for 150 years. I know that I have about 2% Neanderthal ancestry, and I know that because we have genetic sequences from Neanderthals and whole genomes from me and many other people. And I can find the Neanderthal chunks. So one answer to your question, right? What more do we need? Is we got everything we needed and we answered some old questions. The problem is, of course, that that opens new questions. And that's the way science works, right? We've got a new telescope. We can see deeper into the past. We see things they wouldn't,

• 11:59Speaker 02

  we didn't see before. But in the same vein, it creates for us new problems. And we're working to solve those problems with new discoveries of the fossils.

• 12:10Flora Lichtman?

  I mean, is it fossils? Does it come down to just, we need more fossils?

• 12:15Speaker 02

  We always need more fossils. I gotta tell you, right? As somebody who has found a lot of fossils and has described a lot of fossils, I have to say that what I've found and described is a drop in the bucket from what it would take to uncover some of the chapters of our past.

• 12:32Flora Lichtman?

  Dr. John Hawks is an anthropologist at the University of Wisconsin-Madison. John, thanks for joining us today.

• 12:38Speaker 02

  Thank you.

• 12:43Flora Lichtman?

  Today's episode was produced by Dee Peterschmidt, but a lot of folks helped make this show happen every single week, including Annie Nero.

• 12:52Speaker 02

  Jason Rosenberg.

• 12:54Flora Lichtman?

  Sandy Roberts. Robin Kazmer. I'm Flora Lichtman. Thanks for listening.