Posted by jlwile on May 22, 2010
It’s not a really new story, but I was interviewed by an internet radio show about the sequencing of the Neanderthal genome1 and its comparison to present-day people, so I decided I would blog about it as well.
The first thing to discuss is how they sequenced the genome of something that no longer exists. In this case, they used three Neanderthal fossil fragments found in the Vindija cave in Croatia. Fossils (especially those belonging to genus Homo) are rare and very valuable, and this process required the destruction of the fossils, so the three fragments were chosen carefully. They were all fragments that contained very little anatomical information, so anything lost due to the destruction of the fossils was minimal. Based on some pretty good reasoning, it was concluded that the fossil fragments came from three different women, two of which may be relatives. According to scientifically irresponsible dating techniques, these fragments are supposedly around 40 thousand years old.
When they looked at the DNA in the samples they prepared from the bones, they found that between 95 and 99 percent of the DNA came from organisms other than Neanderthals, like bacteria that colonized the fossil. In other words, only 1-5 percent of the DNA found was DNA of interest. How did they get rid of the other 95-99 percent so they could focus on Neanderthal DNA? They used restriction enzymes that tend to cut only bacterial DNA.
So even though this is a remarkable achievement, there are a lot of potential errors in the derived genome sequence. After all, any time the “signal” you are looking at is 20-99 times weaker than the “noise,” it will be hard to determine exactly what the signal is. Keeping in mind these potential errors, what was learned? In short, it was learned that creationists have been right about Neanderthals all along.
As the illustration above shows, when Neanderthal man was first discovered, it was assumed that he was a transitional form between apes and humans. As a result, he was “reconstructed” to be very apelike, despite the fact that the fossils looked very human. Just eight years after the discovery of the first Neanderthal fossil, geologist William King pronounced that Neanderthal man was a completely different species from present-day humans, and he named the species Homo neanderthalensis. The idea that Neanderthal man was a different species from present-day humans has persisted, but creationists have always insisted that Neanderthal man was fully human.
This study, if it holds up, vindicates the creationist position. How does it do that? Well, in the study, the authors compared their Neanderthal genome to the genomes of five present-day humans. The five individuals come from France, China, Papua New Guinea, North Africa, and South Africa. Specifically, they looked at the genome regions that were different among the present-day humans, and they then looked at those regions in the Neanderthal genome to see if the Neanderthal genome was more similar to any of the five current genomes. What they found was that the Neanderthal genome was more similar to the non-Africans than it was to the Africans. This implies that Neanderthals and people interbred.
How do these results imply the interbreeding of Neanderthals and people? Well, the assumption is that if Neanderthals were a distinct population and did not breed with any people, they should be equally unrelated to all present-day humans. However, if some people interbred with Neanderthals, the Neanderthals should be more closely related to the descendants of those people than to the descendants of people with whom no interbreeding took place. Thus, these results indicate that the ancestors of people in Africa did not interbreed with Neanderthals, but the ancestors of the other people represented in the study did interbreed with Neanderthals.
Now, of course, if people and Neanderthals did, indeed, interbreed, then they are clearly from the same species. Thus, this result vindicates what creationists have always claimed. Neanderthals are human beings. They are not some transitional form between ape and human (as was first believed), and they are not some isolated evolutionary dead end (as has been the currently fashionable evolutionary belief). Instead, they are just a specific race of people who went extinct.
The fact that these data belong to the growing list of data which demonstrate the veracity of creationist positions is not, in my mind, the most important aspect of the story. Instead, the important aspect of this story is that it shows how skeptically you should treat the results of any historical science study, including this one.
You see, evolutionists have been trying for years to promote Neanderthals as something less than human. As a result, it was important to portray Neanderthals as not interbreeding with humans. Thus, several studies were performed that “clearly demonstrated” there was no interbreeding between Neanderthals and humans.
For example, in 2004 Dr. Katerina Harvati and her colleagues performed a three-dimensional analysis of several primate skulls, including those of present-day humans and Neanderthals. They concluded that humans and Neanderthals never interbred.2 This led the BBC to report:
The Neanderthals were not close relatives of modern humans and represent a single species quite distinct from our own, scientists say.
In 2008, the mitochondrial DNA of Neanderthal man was sequenced by the same group responsible for the current study. In case you are not aware, there are two places you can find DNA in the eukaryotic cell, which is the kind of cell found in people and animals. You can find it in the nucleus of the cell, but you can also find it in the mitochondria, which are often called the “powerhouses” of the cell. They are given that name because most the process that converts food into energy takes place in the mitochondria.
The DNA that is found in the nucleus is generally just called “DNA,” although it is more properly called “nuclear DNA.” The DNA that is found in the mitochondria is different, and it is called “mitochondrial DNA.” There is significantly less mitochondrial DNA than there is nuclear DNA, so the mitochondrial genome sequence is easier to produce than the nuclear genome sequence. In addition, it is widely thought that only the mother contributes mitochondrial DNA to the child, while both the mother and father contribute nuclear DNA to the child. As a result, the mitochondrial genome is thought to be easier to understand than the nuclear genome.
So what did scientists learn when they compared the Neanderthal mitochondrial genome to the human mitochondrial genome? They determined once again that Neanderthals and humans did not interbreed, at least not enough for Neanderthals to make any lasting contributions to the human mitochondrial genome.3 Indeed, Discover Magazine reported:
Neanderthal DNA Shows They Rarely Interbred With Us Very Different Humans…The team analysed the DNA of 13 genes from the Neanderthal mitochondria and found they were distinctly different to modern humans, suggesting Neanderthals never, or rarely, interbred with early humans.
Now, just two years later, the same group tells us that Neanderthals and humans did, indeed, interbreed enough so that the Neanderthals left a lasting contribution to the present human genome. Why didn’t the mitochondrial DNA show this? According to John Hawks:
The mtDNA of Neandertals is gone because it conferred some disadvantage.
We don’t know what that disadvantage was, but it must have existed, at least according to evolutionary thinking.
So to me, the “take home lesson” of this story is to always be skeptical of new results when it comes to historical science. Up until just two years ago, there were at least two strong lines of evidence that “clearly” showed people and Neanderthals were different species. Today, there is strong evidence that “clearly” shows they are the same species. While I prefer the latter conclusion to the former one, I won’t claim the case is closed. Historical science is fraught with difficulties, and it often takes generations for those difficulties to be uncovered.
2. Harvati K. , Frost S.R. and McNulty K.P., “Neanderthal taxonomy reconsidered: Implications of 3D primate models of intra- and inter-specific differences,” Proceedings of the National Academy of Sciences USA 101:1147-1152, 2004.
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