Re: DNA testing
Thu, 05 Aug 1999 20:46:38 +0000

At 05:32 PM 08/05/1999 -0500, Jeff Schnitker wrote:
> I hope this question is appropriate for this group. I was wondering.
>Has there been any DNA study/testing, or is it possible, on Neanderthal,
>Africa, Peking man to see whether or not theirs is similar to ours. If so,
>what conclusions have been made? Thank you for your time, Jeff Schnitker

The only DNA testing on fossil man comes from the mitochrondrial DNA
recovered from Neanderthal. That data is often claimed to show that
Neanderthal can't be related to us. But, an analysis of the data shows
that this conclusion is a reach. I posted this on a Neanderthal list and
it got me a mention in Anthropological E-mail news which was put out by an
anthropologist at the Chicago Field Museum.

"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)
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. In total, 0.002% of the pairwise comparisions
between human mtDNA sequences were larger than the smallest difference
between the Neandertal and a human.
"The Neandertal sequence, when compared to the mitochondrial
lineages from different continents, differs by 28.2 +/- 1.9 substitutions
from the European lineages, 27.1 +/-2.2 subsitutions from the African
lineages, 27.7+/- 2.1 substitutions from the American lineages and 28.3+/-
3.7 substitutions from the Australian /Oceanic lineages. Thus, whereas the
Neandertals inhabited the same geographic region as contemporary Europeans,
the observed differences between the Neandertal sequence and modern
Europeans do not indicate that it is more closely related to modern
Europeans than to any other population of contemporary humans.
"When the comparison was extended to 16 common chimpanzee
lineages,. the number of positions in common among the human and chimpanzee
sequences was reduced to 333. This reduced the number of human lineages to
986. The average number of differences among humans is 8.0+/- 3.0 (range
1-24), that between humans and the Neandertal, 25.6 +/- 2.2 (range 20-34),
and that between humans and chimpanzees, 55.0 +/- 3.0 (range 46-67). Thus,
the average number of mtDNA sequence differences between modern humans and
the neandertal is about three times that among Humans, but about half of
that between modern humans and modern chimpanzees."Krings, Matthias, et al,
1997. "Neandertal DNA Sequences and the Origin of Modern Humans," Cell,
90:19-30, p. 24-25

It seems to me that the comparison of a range of experimental uncertainty
with mtDNA variation across the human race is an invald comparison.

Secondly, the last paragraph above seems to be an invalid comparison. Since
humans have up to 24 substitutionary differences, and Neandertal is about
that distance from the reference sequence, how can their conclusion that
there is a 3 times difference be meaningful? They further compound this
when 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 time for humans to accumulate 24 substitutions should be almost the
same as the time for Neandertal to accumulate 27 substitutions. While there
may have been isolation between Neandertal women and modern people the time
of divergence should be the same unless they can show that human
mitochondrial substitutions occur at a more rapid rate.


Furthermore, the authors themselves say that this data cannot be used to
prove that Neanderthals left no genetic heritage. They write:

"These results do not rule out the possibility that Neandertals
contributed other genes to modern humans. However, the view that
Neandertals would have contributed little or nothing to the modern human
gene pool is gaining support from studies of molecular genetic variation at
nuclear loci in humans." ~ Matthias Krings, et al., "Neandertal DNA
Sequences and the Origin of Modern Humans," Cell, 90:19-30, p. 27

What this study conclusively does prove is that this particular
neanderthal's mother left no mitochondrial DNA in the human population.
That is not at all the same as saying that she left no genetic legacy. If
she had only sons, then the likelihood of her passing her mtDNA on is very
low, but she could easily have left nuclear genetic material to the future
through her sons.

And if the Neanderthal hybrid is truly a hybrid, then the question of
genetic continuity with archaic peoples is still an open question.

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