The most ancient fossil hominid, announced last week, causes several changes
in the way we view human origins and these changes will have theological
implications. First, the issue of is it a hominid. Usually at these
announcments some creationist organization or apologetical organization will
claim it isn't a hominid. It is. Bipedality is a key criteria of being a
hominid. Indeed, some call it the 'hallmark' of hominid status (Noel Boaz,
Eco Homo, (New York: Basic Books, 1997), p. 139) From what I can see in the
pictures, this creature does show evidence of bipedalism in the placement of
the foramen magnum, the opening at the base of the skull where the spinal
cord enters the brain. In chimps, who walk on all fours, the foramen magnum
is at the back of the skull. If it were underneath the skull, the chimp
would be looking at the ground all the time. If we had a foramen magnus
placed in a chimp-like position, we would be looking at the zenith of the
sky all day. Figure 1:d of the article clearly shows the foramen magnum
underneath the skull. An associated article notes: "And the point at the
back of skull where neck muscles attach suggests that ToumaÔ walked
upright." http://www.nature.com/nsu/020708/020708-12.html. Also supporting
its hominid status are the shape of the foramen magnum, which is oval
(http://www.bartleby.com/107/31.html). Chimp foramen magna are more rounded.
The article lists all the hominid traits:
ìSahelanthropus has several derived hominid features, including small,
apically worn caninesówhich indicate a probable non-honing CñP3 complexóand
intermediate postcanine enamel thickness. Several aspects of the basicranium
(length, horizontal orientation, anterior position of the foramen magnum)
and face (markedly reduced subnasal prognathism with no canine diastema,
large continuous supraorbital torus) are similar to later hominids including
Kenyanthropus and Homo. All these anatomical features indicate that
Sahelanthropus belongs to the hominid clade.îMichel Brunett, et al, ìA New
Hominid from the Upper Miocene of Chad, Central Africa,î Nature,
481(2002):145-152, p. 151
Another associated article notes:
"ToumaÔ has prominent brow ridges of the kind seen only in our own genus,
Homo. " http://www.nature.com/nsu/020708/020708-11.html
There is little doubt of the hominid status of this creature.
Secondly, this skull has implications for the age of mitochondrial Eve. This
is because the rate of mutation is calibrated by the date of the
chimp-hominid split. Given that tchadensis moves the date of that split
further back in time, it means that mitochondrial Eve is now older. It can
be illustrated by the following:
"Hasegawa and Horai (1991) used a different analytical approach to estimate
the time of coalescence from the mitochondrial DNA sequence data. Using a
four-million-year calibration point for the human-chimpanzee divergence,
they estimated a divergence time of 280,000 years ago. Using their variance
estimate in a gamma distribution, the resulting 95% confidence interval is
191,000 to 386,000 years ago. Using a 9.2-million-year calibration point for
the human-chimpanzee divergence, the resulting 95% confidence interval using
the approach of Hasegawa and Horai (1991) is 439,000 to 844,000 years ago.
Consequently, the approach of Hasegawa and Horai (1991) indicates that the
coalescent time is even older than that implied by Tajima's equations." ~
Alan R. Templeton, "The 'Eve" Hypothesis: A Genetic Critique and
Reanalysis," American Anthropologist 95(1): 51-72. p. 59
Sahelanthropus tchadensis pushes the calibration point back towards the 7-9
million year range and that means then that the mitochondrial Eve gets
older, meaning that she is from a time when there were NO anatomically
modern humans on earth. Our Eve is either an archaic Homo sapiens or Homo
Erectus.
"Assuming a human-chimpanzee divergence at 6 my, this corresponds
to a molecular divergence time among modern humans of 222,000
years.
"We also used the combined mitochondrial sequence data from
COII and ND4-5 to estimate coalescence times for human alleles. We
used a variety of mutation rates, which is equivalent to
calibrating with different divergence times between humans and
chimpanzees. Using 6 my for the human-chimpanzee divergence, the
mean coalescence time for human alleles is 298,000 years (somewhat
older than the date derived above using a relative branch length
approach) with 95% coalescent error bars of 129,000 to 536,000
years." MaryEllen Ruvolo, "A New Approach to Studying Modern Human
Origins: Hypothesis Testing with Coalescence Time Distributions,"
Molecular Phylogenetics and Evolution 5(1996):1, p. 202-219, p.
208
Using 7 million years for the split we have the error bars between 150 and
625 kyr with the mean at 347 kyr.
Using 9 million years for the split we have the error bars between 193 and
804 kyr with the mean at 447 kyr.
The oldest fossil of what is called anatomically modern man(they have
archaic features) is found 130,000 years ago at Omo Kibish and Klasies River
Mouth Cave (Chris Stringer and Clive Gamble, In Search of the Neanderthals,
(New York: Thames and Hudson, 1993), p.218; Bernard G. Campbell and James D.
Loy, Humankind Emerging (New York: HarperCollins, 1996), p.466).
With the discovery of Sahelanthropus, Eve just got much older than that.
Thus, Mitochondrial Eve didn't look like us and she wasn't within the past
60,000 years.
glenn
see http://www.glenn.morton.btinternet.co.uk/dmd.htm
for lots of creation/evolution information
anthropology/geology/paleontology/theology\
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