This is a post I made concerning the implications of the Neanderthal mitochondrial DNA which Krings et al. published in 1997.

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I have finally gotten my hands on the Neanderthal DNA articles from Cell (Krings, et al. 1997; Lindahl, 1997). The authors do an excellent job of addressing the questions a skeptic might ask of their results. They used multiple control mechanisms, such as repeating the DNA extraction at two different laboratories, using different experimental techniques, only using data which was experimentally duplicated, etc. In short, I am convinced that they did every thing they could to ensure no contamination and to rule out errors. I believe that they did in fact isolate Neanderthal mtDNA.

What are the implications of this work? First, it demonstrates conclusively that we have no Neanderthal great...great-grandmothers from the lineage of the Neanderthal whose bone was used. The authors make the claim that this work places Neanderthal outside of the range of variation of human mtDNA. This claim is not supported by the data the authors present. Krings et al write:

"Whereas these modern human sequences differ among themselves by an average of 8.0+/- 4.1 (range 1-24) substitutions, the difference between the humans and the Neandertal sequence is 27.2+/-2.2 (range 22-36)" (Krings et al, 1997, p. 24)

They make a big error here by comparing the range of human mtDNA variation (1-24 differences from the standard sequence) with the experimental error in determining the Neanderthal variation (22-36). This is an equivocation.

If Neanderthal mtDNAis outside of the range of human variation, it is only slightly beyond that range and may be within it. The experimentally determined minimal distance between Neandertals and us is 22 substitutions. (Krings et al, 1997, p. 24-25) Modern humans can have as many as 24 substitutions among them, and they are still considered human.

In spite of the press reports, the authors themselves acknowledge that this does not rule out the inclusion of Neandertals in our ancestry. They write,

"These results do not rule out the possibility that Neandertals contributed other genes to modern humans." (Krings et al, 1997, p. 27)

This is because of a phenomenon called crossover. Genetically, the mitochondria only can determine whose mother left her mtDNA in the humans. But other women left their nuclear DNA to us but they didn't leave their mitochondria. There is a phenomenon called cross-over which occurs on all chromosomes except the X and Y. During the formation of the sperm or egg a chromosome makes two copies of each.

000000000000 Chromosome 1 from mother
111111111111 chromosome 1 from father

During meiosis, each doubles and you have this situation:

000000000000 Chromosome 1 from mother
000000000000 Chromosome 1 from mother
111111111111 chromosome 1 from father
111111111111 chromosome 1 from father

Then cross over occurs which scrambles the chromosome's lineage.

000000000000 Chromosome 1 from mother
000000001111 Chromosome 1 from mother and father
111111110000 chromosome 1 from father and mother
111111111111 chromosome 1 from father

This phenomenon occurs rapidly enough so that no one can follow a lineage of nuclear DNA.

The implications are that as long as no direct maternal lineages from Neanderthal exist, there still could be Neanderthal genes in our lineage.

The best evidence of that is from the H-O mandibular foramen. This is a weird type of hole in the jaw where the nerve goes through. There are two types of this foramen: normal and H-O. The H-O foramen is described by Wolpoff and Caspari,

" "The mandibular foramen, for example, is an opening on the inside of the vertical part of the mandible for the branch of the mandibular nerve that reaches the teeth. This is the uncomfortable spot a dentist tries to reach with a nerve block for the mandibular teeth. In the H-O form the rim of the opening has an oval shape with the long axis of the oval oriented horizontally. Alternatively, in the normal form the rim may be broken, along with its lower border, by an unbridged vertical groove. The broken rim is the usual form in living populations. "The horizontal-oval mandibular foramen is virtually unique to European fossils. It is found in almost no other remains, including Late Pleistocene Africans and the Skhul/Qafzeh sample, the putative alternate ancestors of the post-Neandertal Europeans. But the horizontal-oval foramen has a significant frequency in the subsequent post-Neandertal populations of Europe and only decreases to rarity in recent Europeans. The exact form of the foramen opening is an example of nonadaptive equivalents. It is important that the foramen be there (the nerve must enter the mandibular body), but it makes absolutely no difference which form its rim has."~Milford Wolpoff and Rachael Caspari, Race and Human Evolution, (New York: Simon and Schuster, 1997), p. 296-297

In order to explain this without Neanderthal genes in the population of Europe, one must assume that the H-O form arose by mutation a second time, only in European fossils. This is not found in non-European populations!

It is also only found in Neanderthal fossils with one exception. Frayer notes "For example, australopithecines totally lack the trait, and the H-O foramen is exceptionally rare in the fossil record of Homo before the neanderthals. In pre-Mousterian Europe the H-O form is absent in specimens such as Mauer and Arago 2 and 13. Each of these have the normal, V-shaped morphology. From my survey of the literature and inspection of casts and original specimens, the only non-European fossil which possesses the H-O trait is an archaic Homo mandible from Olduvai Gorge (OH-22)."~David W. Frayer, "Evolution at the European Edge: Neanderthal and Upper Paleolithic Relationships," Prehistoire Europeenne, 2:9-69, p. 29

Here are the frequencies of the H-O foramen The African Eves are the anatomically modern humans:

European                H-O         Normal
                      Foramen      Foramen
                         %            %

Neanderthal             53            47
African Eves             0           100 (the invaders)
Skhul/Qafzeh             0           100 (the invaders)
Early U. Paleolithic    18            82 (supposedly genetically separate)
Late U. Paleolithic      7            93
Mesolithic               2            98
Medieval Europeans       1            99

David W. Frayer, "Evolution at the European Edge: Neanderthal and Upper Paleolithic Relationships," Prehistoire Europeenne, 2:9-69, Table 7, p. 31

As to claims of Neanderthal being a different species, this may be quite erroneous and unproven. Even if there has been 550-700,000 years of separation between anatomically modern men and Neanderthals, this does not mean that the Neanderthal were unable to interbreed with us. Consider the coyote and wolf,

"The coyote and wolf have a sequence divergence of 0.075 +/- 0.002 and diverged about one million years ago, as estimated from the fossil record. consequently, because the sequence divergence between the most different genotypes in clade 1 (the most diverse group of dog sequences) is no more than 0.010, this implies that dogs could have originated as much as 135,000 years ago. "~Carles Vila et al, "Multiple and Ancient Origins of the Domestic Dog," Science, 276(June 13, 1997):1687-1689, p. 1689

Why is this important? Because the coyote and wolf can mate and produce fertile offspring, some believe that they are really the same species and according to some definitions they would be. If coyote and wolf, which diverged more than a million years ago, and Neanderthal diverged only 600,000 years ago, why must we automatically feel that they are a different species? While I haven't seen the Cell article, I will bet that the divergence is less than .075 because Neanderthal and modern man diverged according to the report, 500-600,000 years ago.

Finally, there is a morphological intermediate between Neanderthal and archaic Homo sapiens in the Atapuerca people I mentioned on some posts about the earliest burial. They lived about 600kyr ago and are at the perfect time for the split between the lineages. If those people are the ancestors of Neanderthal, and they were human, with burial rites, then their descendants, the Neanderthals, also would have to be people.

I think the biggest disappointment was the authors' using out of date articles to date the origin date of modern men. They did not even reference Templeton's work which most authorities agree, destroyed the 120-150,000 year old Eve theory. There still was an Eve, but Eve was much older. As noted above, there are up to 24 differences in the mtDNA of modern humans. This requires some time for this amount of divergence to occur. They write:

"To estimate the time when the most recent ancestral sequence common to the Neandertal and modern human mtDNA sequences existed, we used an estimated divergence date between humans and chimpanzees of 4-5 million years ag and corrected the observed sequence differences for multiple substitutions at the same nucleotide site. This yielded a date of 550,000 to 690,000 years before present for the divergence of the Neandertal mtDNA and contemporary human mtDNAs. When the age of the modern human mtDNA ancestor is estimated using the same procedure, a date of 120,000 to 150,000 years is obtained, in agreement with previous estimates.(Cann et al., 1987 Vigilant et al. 1991)." Krings, Matthias, et al, 1997. "Neandertal DNA Sequences and the Origin of Modern Humans," Cell,90:19-30, p. 25

The authors are obviously using two different rates (or alternatively a different amount of divergence) to estimate the divergence of modern human mtDNA and that of Neandertal. The time it took for modern human populations to accumulate 24 differences among themselves, can not be significantly less time than it took for Neandertal to accumulate 27 differences. Yet the authors seem to indicate that it was. Mathematically, this is fallacious.

The Cann et al and Vigilant articles have been disproven by the work of Alan Templeton (Templeton, 1993). Trinkaus and Shipman write:

"Templeton also challenged the calibration of the molecular clock used by the mtDNA researchers. Instead of trying to pinpoint a specific date at which the mtDNA in all modern human groups separated evolutionarily, Templeton estimated the 95 percent confidence limits on that time. In other words, he defined a divergence period by picking the most recent likely date and the most ancient likely date, between which there was a period when the divergence actually occurred, with 95 percent certainty. Basing his work on conservative assumptions, Templeton showed that the mtDNA divergence lay not in the relatively narrow band of time between 166,000 and 249,000 years ago, as had previously been estimated, but in a broad swath sometime between 191,000 and 772,000 years ago. This time interval embraces the period in which Homo erectus was spreading out of Africa and across Eurasia--meaning that the divergence in mtDNA might well have occurred long before the appearance of modern humans." (Trinkaus and Shipman, 1993, p. 394-396)

This can be calculated easily. If modern humans have a divergence of 24 sequence differences, and Neanderthals have a divergence from modern humans of 27 sequence differences, then at the least, modern humans should have split apart from each other only 24/27ths of the time of the Neanderthal split. So if the Neandertal split 600,000 years ago, the rest of humanity should have split from themselves at 533,000 years ago. This is not a lot of difference. Templeton lists a variety of divergence times for Eve ranging from 280,000 to 844,000 years for the length of time it took for the observed variation in modern human mtDNA to arise. (Templeton, 1993, p. 59).

Finally, since the ability to reproduce fertile offspring is determined by nuclear DNA, not mtDNA, these differences shed no light on whether or not we are different species.

Theologically, if Christians use this to say that Neanderthals are not human, then that is equivalent to saying that humanity is determined by mitochondrial DNA. All humans do not have the same mitochondrial DNA sequence, and in fact are almost as divergent from each other as they are from this Neanderthal. If the Neandertal is not human, then what about those populations today whose mtDNA is so divergent from the norm? Are they also not human? To use mtDNA to exlcude the Neandertal from humanity implies that humanity is defined by mtDNA, which is a very dubious proposition.

DMD Publishing

References

Krings, Matthias, et al, 1997. "Neandertal DNA Sequences and the Origin of Modern Humans," Cell, 90:19-30.

Lindahl, Tomas, 1997. "Facts and Artifacts of Ancient DNA," Cell, 90:1-3.

Templeton, Alan R. 1995 "The 'Eve" Hypothesis: A Genetic Critique and Reanalysis," American Anthropologist 95(1): 51-72. p. 58

Trinkaus, Erik and Pat Shipman, 1993. The Neandertals, (New York: Alfred Knopf).