I am riding a bit of a hobby horse on molecular datings linked to
supposed key events in human evolution, and Sharon Begley's article in
the latest Newsweek quotes a whole lot of them.http://www.msnbc.msn.com/id/17542627/site/newsweek/
Whoever's briefing her has a lot to answer for, since, if both the
AMNH and Newsweek are disseminating such, the 'findings' become
engraved in stone as gospel truth in the public mind, and more than
probably, in such discussion groups as this.
Today I tried to track each one of Begley's pronouncements down to the
original paper, but came across secured access articles (particularly
in Science) which sometimes stopped me in my tracks.
But I did find one outstanding misquote, one extraordinary
interpretation of a crucial date, and a few other wilful
misinterpretations:
(Please bear with me - this is a long and detailed post, thick with
quotes, and I can't put necessary emphasis anywhere)
------------------------------
MRCA of all modern men:
Sharon Begley (Quote):
"Peter Underhill, a molecular anthropologist at Stanford University,
tracked 160 such changes in the Y's of 1,062 men from 21 populations
across the world. Applying the molecular-clock technique, he concludes
that the most recent common ancestor of all men alive today lived
89,000 years ago in Africa. The first modern humans—and therefore,
unlike the earlier wave of Homo erectus into Asia a million years ago,
the ancestors of everyone today—departed Africa about 66,000 years
ago."
Peter Underhill said nothing of the sort.
What he did say was:
"A minority of contemporary East Africans and Khoisan represent the
descendants of the most ancestral patrilineages of anatomically modern
humans that left Africa between 35,000 and 89,000 years ago.
This puts the age of M168, which marks the expansion of anatomically
modern humans out of Africa, at approximately 44,000 years, in
agreement with a previous estimate of 47,000 years with 95%
probability intervals of 35,000–89,000 years using the program
GENETREE"
Y chromosome sequence variation and the history of human populations
PA Underhill, P Shen, AA Lin, L Jin, G Passarino,+ 16 other authors
… - nature genetics,
2000http://tinyurl.com/2h5vp8
I cannot track down Begley's 66000 year figure at all, after an
exhaustive search.
Perhaps I am missing something that someone else came up with.
----------------------------------
FOXP2
Sharon Begley (Quote):
"Using the standard molecular-clock tactic, Svante Paabo and
colleagues at the Max Planck Institute estimate that the human version
of FOXP2 appeared less than 200,000 years ago—about when anatomically
modern humans stepped onto the world stage—and maybe as recently as
50,000. If so, then it is only humans as modern as those in the last
diaspora out of Africa who developed advanced, spoken language."
The paper quoted was written by 7 authors, with Svente Paabo placed
last (that usually means a well-known authority is given some
overseeing role in the paper, not necessarily that he oversaw the
research himself).
They actually said:
"If this speculation is true, then the time when such a FOXP2 variant
became fixed in the human population may be pertinent with regard to
the evolution of human language. We estimated this time point using a
likelihood approach. Under a model of a randomly mating population of
constant size, the most likely date since the
fixation of the beneficial allele is 0, with approximate 95%
confidence intervals of 0 and 120,000 years. Our point-estimate of 0
reflects the fact that high-frequency alleles rapidly drift to
fixation, so an excess is most likely
immediately after a selective sweep.
However, if population growth soon succeeds the fixation of the
advantageous allele, the rate of drift will be decreased and high
frequency alleles may persist longer in the population. Thus, the
inclusion of population growth may push this time estimate back by at
most the time since the onset of human population growth,
some 10,000–100,000 years ago.
In any case, our method suggests that the fixation occurred during the
last 200,000 years of human history, that is, concomitant with or
subsequent to the emergence of anatomically modern humans. This is
compatible
with a model in which the expansion of modern humans was driven by the
appearance of a more-proficient spoken language"
Molecular evolution of FOXP2, a gene involved in speech and language
Wolfgang Enard*, Molly Przeworski*, Simon E. Fisher†, Cecilia S. L.
Lai†,
Victor Wiebe*, Takashi Kitano*, Anthony P. Monaco† & Svante Pa¨a¨bo*
… - Cell. Biol, 2001 - botany.utoronto.cahttp://tinyurl.com/29cv4u
- which is a quite extraordinary conclusion, based on:
"the most likely date since the fixation of the beneficial allele is
0, with
approximate 95% confidence intervals of 0 and 120,000 years."
Put less 'scientifically' this means the FOXP2 variant most probably
happened sometime between July 4 2001 AD and 120000 BC, or at most,
between 10kya and 100kya, and certainly in the last 200,000 years - a
very good series of fail-safe statements.
50,000 years ago wasn’t mentioned at all.
What it certainly doesn't say is that the FOXP2 variant was really any
'cause' for the introduction of a more-proficient spoken language, or
that it coincided in any way with appearance of modern humans, or with
any supposed intellectual explosion 50,000 years ago.
-----------------------------------
A few other wilful misinterpretations:
------------------------------------
ASPM:
Sharon Begley (Quote):
"The third, called ASPM and also involved in brain size, clocks in at
5,800 years.
That was just before people established the first cities in the Near
East and is well after Homo sapiens attained their modern form."
The researchers actually said:
"...one genetic variant of ASPM in humans arose merely about 5800
years ago"
Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in Homo
sapiens
Mekel-Bobrov et al Science 9 September 2005:Vol. 309. no. 5741, pp.
1720 - 1722
Science - (Secured article)
- abstract
onlyhttp://tinyurl.com/kmrxr
This is a bit different than stating, baldly, that something new,
ASPM, clocked in 5,800 years ago, just as we invented cities.
-------------------------------------
PDYN
Sharon Begley (Quote):
"In 2005, Matthew Rockman of Duke University and colleagues discovered
that a gene called PDYN began accumulating changes 7 million years
ago, soon after our oldest direct ancestor appeared".
The authors actually said:
"If instead of divergence, we consider the germline mutation rate,
estimated at 0.99 3 10 9 per site, and assuming 5 to 7 million years
of evolution since the last common ancestor of humans and chimpanzees,
we expect 0.34 to 0.47 substitutions per 68 bp. To convert the
acceleration factor to s, we consider the case of sequential fixations
and ignore the effect of interference among independent advantageous
mutations. The effect of interference is likely to be modest, as the
expectation of the conditional fixation time of advantageous alleles, ;
(2/s)(ln2N) , is less than 10,000 generations for s . 0.002, while the
time available for fixations is roughly 300,000 generations (6 million
years, 20 years per generation)."
Ancient and Recent Positive Selection Transformed Opioid cis-
Regulation in Humans
MV Rockman, MW Hahn, N Soranzo, F Zimprich, DB …
- biology.plosjournals.orghttp://tinyurl.com/24dung
which doesn't, at all, say quite the same.
----------------------------------------
Human/chimp MRCA
Sharon Begley (Quote):
"....7 million years ago, soon after our oldest direct ancestor
appeared".
The authors of the PDYN paper cite:
Slow Molecular Clocks in Old World Monkeys, Apes, and Humans
S Yi, DL Ellsworth, WH Li - Molecular Biology and Evolution,
2002http://www.biology.gatech.edu/professors/yi/clock.pdf
for their 7 million year date, and in turn, the authors of that paper
say:
"Next we take advantage of the recent discovery of a hominid fossil,
Sahelanthropus tchadensis (Brunet et
al. 2002), which was dated to be 6–7 MYA before present (Vignaud et
al. 2002). This is even older than the
earliest known fossil hominid so far, the Ardipithecus ramidus
kadabba, dated to be 5.2–5.8 MYA before present
(Haile-Selassie 2001). As the Sahelanthropus fossil is hominid, it
gives a minimal date of 6 MYA for the
divergence between human and chimpanzee. (Note that as long as
Sahelanthropus was a hominid, the fossil
would have postdated the human-chimpanzee divergence, even if it was
not a direct ancestor of Homo
sapiens.) We therefore obtain a maximal rate of 0.99 3 1029
substitutions per site per year for the human and
chimpanzee lineages. The actual human-chimp divergence should be older
than the Sahelanthropus hominid
fossil, which can be as old as 7 MYA (Vignaud et al. 2002). If we
assume that the date for the human-chimp
split is 7.5 MYA, then the average substitution rate in noncoding,
nonrepetitive regions becomes 0.79 3 1029
substitutions per site per year."
In other words, they fiddle their figures to fit Toumai, whose
putative date is, anyway, very embarrassing to any estimates of the
dating of the Human/chimp MRCA. And they’re not estimating the date of
the human/chimp MRCA at all, but investigating gene change rates.
-----------------------------
If Ian Tattersall is behind all this wilful misinterpretation of
reported data, to fit his own agenda, then that puts him in the same
league as Dick Cheney.
I don't think he would appreciate such a comparison at all.
regards
Richard
