Comment on Dr. Geraty clarifies his “Challenge” to literal 6-day creationism by Sean Pitman.

“Species” based on mtDNA phylogenies?

As far as the topic of human ethnic groups compared to various “species” definitions for animals, consider the case of the Neanderthal. Many scientists consider Neanderthals to have been a separate “species” of human – not just a unique ethnic variation. This is due to several unique morphologic features of Neanderthals compared to modern humans – as well as to unique DNA sequences and average numbers of mutational differences.

According to a 1997 study by Pääbo et. al., on certain mtDNA sequences of Neanderthals compared to modern humans, Neanderthals would seem to qualify as a unique “species” – and not just a “cryptic species” due to their prominent morphologic differences.

“The Neandertal sequence was compared to 994 contemporary human mitochondrial lineages, i.e., distinct sequences occurring in one or more individuals, found in 478 Africans, 510 Europeans, 494 Asians, 167 Native Americans and 20 individuals from Australia and Oceania. Whereas these modern human sequences differ among themselves by an average of 8.0 (range 1-24) substitutions, the difference between the humans and the Neandertal sequence is 27.2 (range 22-36) substitutions. Thus, the largest difference observed between any two human sequences was two substitutions larger than the smallest difference between a human and the Neandertal…

The Neandertal mtDNA sequence thus supports a scenario in which modern humans arose recently in Africa as a distinct species and replaced Neandertals with little or no interbreeding.”

If mtDNA was in fact isolated from the Neanderthal bones, these conclusions might seem reasonable until one considers a few more facts. The Cell article itself noted that the range of sequence differences for modern human mtDNA goes from 1 to 24 with an average of 8 substitutions. The mtDNA sequence differences between modern humans and the single Neanderthal fossil range from 22 to 36 substitutions, with the average being 27. In other words, the two most different humans analyzed in this study, as far as mtDNA substitutions are concerned, are different by 24 substitutions. The closest that any human in this study was to the single specimen of Neanderthal mtDNA was 22 substitutions. This means that there are some people living today that are closer to Neanderthals in their mtDNA sequencing than they are to some other modern human beings. Someone might be found to be only 22 substitutions away from our Neanderthal, but 24 substitutions away from his own next-door neighbor. Interesting isn’t it? If Neanderthals are classed as separate species because of these differences, which one of our modern human volunteers should be classify as a separate species? Perhaps the one who was only 22 substitutions different from the Neanderthal? Or, maybe his next-door neighbor who is 24 substitutions away from his neighbor as well as 22 substitutions away from our Neanderthal friend? I mean, some of us might have neighbors that look like Neanderthals (or maybe we might look like Neanderthals compared to our neighbors), but can a different species really be assumed based on a difference of 20-some substitutions in a particular hypervariable region of DNA?

That means that there are a few modern humans who differ by 24 substitutions from a few other modern humans—two substitutions more than the Neanderthal individual. Would not logic demand that those few modern humans living today should also be placed in a separate species? To state the question is to reveal the absurdity of using such differences as a measure of species distinctions.

Lubenow, Marvin (1998), “Recovery of Neandertal mtDNA: An Evaluation,” CEN Technical Journal, 12[1]:87-97.

A subsequent paper published by Pääbo and his team in May of 1999, show that the range (1-81) for chimp/bonobo substitutions (in certain regions of mtDNA) are even wider than previously thought. In other words, if one chose a chimp at random, this chimp might be as many as 81 substitutions different from the chimp swinging on the branches right next to him. This is interesting because this same chimp might be only 78 substitutions different from a given modern human. This more recent paper also points out that the range between humans (1-35) is also wider than was reported in the first paper. The range between humans and the Neanderthal sequence was also altered in the updated paper to (29-43).

This second paper seems to make it even more clear that substitution differences in a given variable region cannot be used to absolutely measure the boundary between different species. In fact, using this method of reason, it seems like some chimps might be more closely related to certain humans than to certain chimps within their own species. Since this clearly is not the case, this logic seems flawed. Evolutionary conclusions therefore cannot be effectively supported using this these methods.

Of course, there is an additional problem that some humans from certain ethic groups are more closely “related” to Neanderthals than they are to certain other living humans from other groups. The question remains as to who should be classed as a separate species?

Maryellen Ruvolo (Harvard University) points out that the genetic variation between the modern human and Neanderthal sequences is within the range of other single species of primates. She goes on to say: “there isn’t a yardstick for genetic difference upon which you can define a species.”

Further confusion comes from the comments in the Cell article that seem to indicate that Neanderthals are more closely related to the ancestral “chimpanzee” than modern humans are. This might not have been the actual intention of the authors, but one could easily get confused by the wording of the article. The fact of the matter is that the single specimen of Neanderthal mtDNA was actually farther away from chimp mtDNA than humans are from chimp mtDNA substitutions. Clearly then, Neanderthal DNA is no closer “related” to chimp DNA than human DNA is.

Add to all of this the fact that the popular notion that mtDNA mutations can be used as a molecular clock has been called into question by the journal Science. As it turns out, former ideas about the timing of this clock might be in error by as much as “20-fold” – (or even 100 fold based on other studies). The famous “Mitochondrial Eve” once thought to be around 100,000 to 200,000 years old, might now have to be revised to as young as “6,000” years old.

D. Melnick and G. Hoelzer (Columbia University) tested the assumptions of mtDNA based phylogenic relationships and concluded:

“Our results suggest serious problems with use of mtDNA to estimate ‘true’ population genetic structure, to date cladogenic events, and in some cases, to construct phylogenies.”

If that isn’t an understatement of the problem I don’t know what is?

Jonathan Marks (Yale University) declared mtDNA determined relationships to be highly biased:

“Most analysis of mitochondrial DNA are so equivocal as to render a clear solution impossible, the preferred phylogeny relying critically on the choice of outgroup and clustering technique.”

In August of 2002, Gabriel Guitierrez et al., from the Universidad de Sevilla, Spain, published a paper in the well known journal, Molecular Biology and Evolution entitled, “A Reanalysis of the Ancient Mitochondrial DNA Sequences Recovered from Neandertal Bones.” Consider some of their conclusions:

Recent reports analyzing mitochondrial DNA sequences from Neandertal bones have claimed that Neadnertals and modern humans are different species. The phylogenetic analyses carried out in these articles did not take into account the high substitution rate variation among sites observed in the human mitochondrial D-loop region and also lack an estimation of the parameters of the nucleotide substitution model…

The computation of pairwise distances between 171 randomly selected sequences and the Neandertals rendered 1.6% of human-human comparisons larger than the smallest difference between Neandertals and humans. Likewise, 27% of the comparisons are lower than the largest human-human difference. This result suggests that Neandertals sequences are not so different from those of extant humans, in contrast to the NSG claims…

The main conclusion can be extracted from our analyses: the phylogenetic position of the ancient DNA sequences recovered from Neandertal bones is sensitive to the phylogenetic methods employed. It depends on the model of nucleotide substitution, the branch support method, and the set of data used.

In fact, Guitierrez et. al. went on to show that depending upon the mtDNA region(s) chosen Neaderthals could be clustered with modern humans while certain ethnic groups could be isolated out as separate “species” groups. This only highlights the subjective nature and definition of “species” using mtDNA-based phylogenies.

Although the molecular data appears to be very objective and precise, John Marcus states that the interpretation of the molecular data is just as subjective as is the interpretation of the fossils. Not only is the molecular evidence unfalsifiable, but

‘… the scientist must always choose which piece(s) of DNA he is going to use to do his comparisons. Very often a particular piece of DNA will not give the “right” answer and so it is dismissed as a poor indicator of the evolutionary process’.

Kenneth A.R. Kennedy (Cornell University) comments:

‘This practice of forcing the paleontological and archaeological data to conform to the evolutionary and genetic models continues in reinterpretations of dates based upon the molecular clock of mitochondrial DNA as well as radiometric samples… .’

The misinterpretation of the mtDNA data is seen in the work of Pääbo and his associates in that the Neandertal fossil evidence contradicts their interpretation of the mtDNA evidence.

http://www.answersingenesis.org/tj/v12/i1/mtdna.asp#f47

These same problems are not likely to be restricted to the determination of hominid “species” and phylogenetic relationships but are likely to affect the determination of different animal species as well – to include the numerous “cryptic species” that are being discovered today…

For further discussion of this topic see:

http://www.detectingdesign.com/earlyman.html#Neanderthal

Sean Pitman
www.DetectingDesign.com

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