Genetic Study Confirms Dr. Craig's Model

KEVIN HARRIS: Dr. Craig, this study we are looking at is very timely with your book on the historical Adam. Very importantly, the findings support a speciation event that is right in line with the model that you spell out in your book. We’ll visit that in just a moment. This genetic study reported in the journal Science has also been written up in the New York Times which says^[1],

But as omnipresent as humans may be today, a team of scientists now claims that our species came very close to never appearing at all.

Researchers in China have found evidence suggesting that 930,000 years ago, the ancestors of modern humans suffered a massive population crash. They point to a drastic change to the climate that occurred around that time as the cause.

Our ancestors remained at low numbers — fewer than 1,280 breeding individuals — during a period known as a bottleneck. It lasted for over 100,000 years before the population rebounded.

Let's start with the bottleneck. What is that?

DR. CRAIG: A bottleneck is a metaphor for a decline in the population as you go back in time. Think of the shape of a bottle which is wide in circumference around the base but then as you go toward the neck of the bottle it narrows down. What they have discovered is that around 900,000 years ago the population of breeding human beings on this planet went down to a severe bottleneck for a period of about 100,000 years. The genetic data indicates that there were less than 1,300 breeding individuals on average over that period of 100,000 years. So the human population as you go back in time constricts down to this very tiny narrow bottleneck right around 900,000 years ago.

KEVIN HARRIS: Would you say that your book, In Quest of the Historical Adam, is a proposal or a model that makes predictions? What I'm trying to say is all models predict what one should expect will be discovered if the model is accurate. So far, is this study in line with your model?

DR. CRAIG: It is absolutely in line with my model. I have to say that I did not propose a model that had any predictable results from it. I simply wanted to craft a hypothesis that would be consistent with all of the known scientific evidence. So my hypothesis was that the human race sprang from an original single founding pair called Adam and Eve prior to 750,000 years ago. Now, I never imagined that there would actually be scientific evidence that would confirm this hypothesis. All of the data that we had was that there could be such a population bottleneck if it was prior to 500,000 years ago. If it was prior to 500,000 years ago we wouldn't be able to detect it so as to say it didn't happen. So the evidence we had was just negative – it did not rule out such a population bottleneck as long it was earlier than 500,000 years ago. But now what this genetic study indicates is that there actually was such a bottleneck around 900,000 years ago during which the human population was so small that it was less than 1,300 breeding individuals over a window of about 100,000 years. This is dramatic scientific confirmation of my model. Beyond my wildest dreams I could not have imagined that we would have this. Now, our listeners need to understand that when one speaks of scientific confirmation we don't mean scientific proof. When you say a hypothesis has been confirmed what one means is that given the new evidence the probability of the hypothesis is increased. The hypothesis is more probable given this new evidence than it was before. And this new genetic evidence provides significant scientific confirmation of my model. It makes the model significantly more probable than it would have been in the absence of this evidence.

KEVIN HARRIS: I think you had some divine help with this! The New York Times article says,

“About 98.7 percent of human ancestors were lost at the beginning of the bottleneck, thus threatening our ancestors with extinction,” . . .

If the research holds up, it will have provocative implications. It raises the possibility that a climate-driven bottleneck helped split early humans into two evolutionary lineages — one that eventually gave rise to Neanderthals, the other to modern humans.

DR. CRAIG: Let me interrupt at this point. You notice that these scientists are presupposing the truth of standard evolutionary biology, namely that human beings evolved from nonhuman primates who lived earlier. So they talk about a crash in these nonhuman ancestral forms prior to the bottleneck, and then you have the bottleneck and then the human population beginning to emerge. This is consistent with my model saying that the human population actually originated prior to that bottleneck. My model doesn't say anything about human evolution from lower primate forms. This has been a misunderstanding of the book by some people. It is neutral with respect to that. The model is consistent with saying that there were ancestral primates to the human population, but it's also consistent with a de novo creation of the founding pair of Adam and Eve by God at the beginning of this population bottleneck. So my model is neutral with respect to the question of what went before the bottleneck.

KEVIN HARRIS: This is a little bit of a side issue but I am curious about it. I want to mention the possible political baggage that this New York Times article carries. Anytime climate change is mentioned, it triggers the divisive global warming controversy, but catastrophic climate changes have always been a part of Earth's natural history so that needs to be taken into account. But I wonder if the New York Times sees this near-extinction that is evident in this study as a warning on the side of the global warming debate.

DR. CRAIG: Yeah, I wondered that, too. When they use those trigger words “climate change” you wonder what they're thinking of. Now, it may have been that they were simply thinking of the Ice Age or an ice age during which the population was tremendously attrited because of the difficult living conditions during those cold years. So that's possible that they're talking about the Ice Age, but they didn't explain this in the article. There they are simply speculating as to what the cause of the bottleneck is. Their genetic modeling indicates merely that the human population does go back to this severely restricted early tiny population but it doesn't say anything about how that originated.

KEVIN HARRIS: Oh, and on Neanderthals, Bill. You spell out in your book that they should be considered human.

DR. CRAIG: Exactly. One of the things that was so important for me in this investigation was the conviction that I arrived at on the basis of the archaeological evidence as well as the skeletal evidence is that Neanderthals were fully human, that they were our human cousins. They were just as intelligent as Homo sapiens, and therefore deserve to be called fully human. Indeed, some people think that because Neanderthals and Homo sapiens interbred with one another, and only members of the same species can successfully interbreed, that in fact they really were members of our species – that they were all one human species – and they would be just like a different race perhaps. But nevertheless all fully human.

KEVIN HARRIS: The article continues,

For decades now, scientists have reconstructed the history of our species by analyzing the genes of living people. . . .

By comparing genetic variations in DNA, scientists can trace people’s ancestry to ancient populations that lived in different parts of the world, moved around and interbred. They can even infer the size of those populations at different times in history.

. . .

Every human genome contains over three billion genetic letters of DNA, each of which has been passed down for thousands or millions of years — creating a vast record of our history. To read that history, researchers now use increasingly powerful computers that can carry out the vast numbers of calculations required for more realistic models of human evolution.

Do you think these new innovations in genetic research are crucial in constructing a scientifically solid view of Adam and Eve?

DR. CRAIG: I don't think they're crucial because I arrived at my model before these results came out. What the evidence indicated, as I say, when I wrote was that there could be such a population bottleneck so long as it was prior to 500,000 years ago. So it was entirely consistent with the evidence. So the model was scientifically credible. But I did not anticipate that there would be actual scientific evidence for the model which we do now have. So it's not crucial but it certainly does make the model significantly more probable.

KEVIN HARRIS: The article continues,

Haipeng Li, an evolutionary genomics researcher at Chinese Academy of Sciences in Shanghai, and his colleagues spent over a decade creating their own method for reconstructing evolution.

The researchers named the method FitCoal (short for Fast Infinitesimal Time Coalescent). FitCoal lets scientists cut up history into fine slices of time, allowing them to create a model of a million years of evolution divided into periods of months.

. . . once enough genetic data from our own species had been sequenced, they turned to the history of humans, comparing the genomes of 3,154 people from 50 populations around the world.

Does it look like FitCoal is going to be an accurate method?

DR. CRAIG: Well, I'm not qualified to answer that question at all. That would be a question more appropriately put to someone like my colleague Josh Swamidass who is an information biologist and who has done genetic modeling of the human population going into the past. What I can simply do is read the scientific literature and report on it, and we'll see whether or not the estimates of this team of geneticists are confirmed by other scientists going forward or whether or not they might be disconfirmed.

KEVIN HARRIS: Did you notice FitCoal is short for “Fast Infinitesimal Time Coalescent” which has definitions of being infinite, but I think it's just shorthand perhaps of what they're trying to call it.

DR. CRAIG: Yes. It's a very fine-grained method for estimating population sizes in the past so that they are able to say that during this era that we mentioned that there were fewer than 1,300 breeding individuals on this planet in the human race. That's just astonishing to think that a model could become so specific, but that's what these new genetic models that they've developed enable them to do.

KEVIN HARRIS: The Times article continues,

The researchers explored various models in order to find one that best explains today’s genetic diversity among humans. They ended up with a scenario that included a near-extinction event among our ancestors 930,000 years ago.

. . .

Before the bottleneck, the scientists concluded, the population of our ancestors included about 98,000 breeding individuals. It then shrank to fewer than 1,280 and stayed that small for 117,000 years. Then the population rebounded.

This small population size seems to have gotten your attention. Why is that?

DR. CRAIG: The reason it's significant is that this average population size of less than 1,300 breeding individuals is an average over that window of about 100,000 years, and so that's entirely consistent with saying that at certain points during that 100,000 years it dipped down even lower or may have risen higher. It's an average over that window of time, and so the data is entirely consistent with saying that during that window of time the population size of the human race shrank down to two as you go back in time – that is to say, to a founding pair from whom all humanity then descended. Now, whether or not there were 98,000 breeding individuals prior to that first pair is going to depend upon whether or not you accept evolutionary theory with regard to their origin. These 98,000 would be nonhuman primate hominids (perhaps something like Homo erectus) from which then the human population evolved. But my model doesn't take a stand on where this original couple came from – how they came to exist – just simply that they existed about this time and the entire human race is descended from that primordial founding pair.

KEVIN HARRIS: Next the article says,

Our branch of the evolutionary tree split from that of other apes about seven million years ago in Africa. Our ancestors had evolved to be tall and big-brained in Africa by about a million years ago. Afterward, some of those early humans spread out to Europe and Asia, evolving into Neanderthals and their cousins, the Denisovans.

The Denisovans are first mentioned on page 276 of your book. Let's revisit that.

DR. CRAIG: Well, let's back up a moment here. Again, they're talking about prehuman evolutionary theory here – things like Australopithecines and other advanced primates. For all we know, these lineages just all died out and became extinct. We do not know that the original founding human pair was an evolutionary product of these individuals. They might have been, but we don't know. So that's what they're talking about over a million years ago in Africa – are these prehuman hominids. Now, when you talk about Neanderthals and Denisovans, you are leaping forward in time hundreds of thousands of years in Asia. Neanderthals diverged from another race of human beings called Denisovans about which we know very, very little because scant remains of their skeletons have been found. But these seem to be three of the major groups of the human species: the Neanderthals, the Denisovans, and then Homo sapiens to which you and I belong. All three of these interbred with one another in the course of their history before the race of Neanderthals and Denisovans went extinct.

KEVIN HARRIS: Continuing the article,

After decades of fossil hunting, the record of ancient human relatives remains relatively scarce in Africa in the period between 950,000 and 650,000 years ago. The new study offers a potential explanation: there just weren’t enough people to leave behind many remains, Dr. Hu said.

That's another thing about this issue. It's difficult to zero in on what ancient humans were like because it was so long ago and remains are relatively scarce.

DR. CRAIG: Oh, extremely scarce. And it's interesting that they think this might be a possible explanation for the scarcity of human remains from this time because there just weren't very many human beings on the planet at that time.

KEVIN HARRIS: Towards the end of the article it says,

Dr. Li and his colleagues also drew attention to the fact that modern humans appear to have split from Neanderthals and Denisovans after their proposed population crash. They speculate that the two events are related.

Now let's get to an important finding in this study that relates to the model that you propose in your book. The study says,

. . . the ancient severe bottleneck possibly marks a speciation event leading to the emergence of the LCA shared by Denisovans, Neanderthals, and modern humans whose divergence has been dated to about 765 to 550 kyr BP.^[2]

Are they referring to Heidelberg man?

DR. CRAIG: Yes! When I read this I nearly came out of my chair. They say that associated with this population bottleneck may have been a speciation event; that is to say, an event which led to the emergence of the last common ancestor shared by Neanderthals, Denisovans, and Homo sapiens (that's what LCA means – it's the last common ancestor). In the article they identify this last common ancestor as Homo heidelbergensis. This was perhaps the most bold prediction of my hypothesis, namely that Adam and Eve were members of the species Homo heidelbergensis from which then all of these other types of human beings evolved. So when these Chinese geneticists came to the conclusion that associated with this bottleneck was the emergence of a new species – Homo heidelbergensis – from which all the rest of humanity descended, I just could not believe my eyes because this was dramatic scientific confirmation of my hypothesis concerning Adam and Eve.

KEVIN HARRIS: As we wrap it up today, you had a chance to talk about this study briefly when we met with several Reasonable Faith chapter directors recently. What are some of the findings in this study that we should keep an eye on?

DR. CRAIG: I think obviously we will want to see whether or not other teams of geneticists confirm these results. When these studies are checked and the models are run again, do other scientific teams also detect this same bottleneck about the same time? Is there any evidence further for this being the origin of the species Homo heidelbergensis? These are some of the questions that we’ll be following the headlines on.^[3]