This wasn't received by the Reflector, so I am resending it.
Apologies if its received twice.
On Thu, 20 Jun 1996 12:08:17 -0500, Steve Clark wrote:
SC>John asks a penetrating question:
JR>I often hear that a given primate species (say, chimpanzees) are
98% or 99% >identical to human wrt the genome.
>Is this literally true? What, exactly, is the claim being made here? How
>do they know without sequencing the whole thing? By "identical" do they
>just mean "similar" or compatible or something more vague like that, or do
>they mean base-pair-for-base-pair identical?
>And how identical are two randomly selected humans? (I've heard informally
>over 99.6%) or two siblings?
>If you know a better question that I would be asking if I knew more about
>it, feel free to answer that one instead or (preferably) in addition.
SC>I only recently heard the claim that humans and chimps share
>90-something% genomic identity. I heard this from Prof. R.J.
>(Sam) Berry, a Christian geneticist from the Univ. of London,
>during a talk he gave on this campus entitled, "Developing a
>Christian Mind". As I recall, the number comes from someone at UCLA
>who proposes that humans and chimps should be considered part of the
>same genus (Homo) but different species. Currently, chimps belong
>to a different genus (Pan).
The study was King M.C. & Wilson A. C., "Evolution at two levels in
humans and chimpanzees", Science, 188:107-116, 1975:
"...Mary-Claire King and A. C. Wilson have recently published an
account of genetic differences between the two species (Science,
April 11, 1975), and the results may well upset a prior prejudice
still
carried, I suspect, by most of us. In short, using all the
biochemical
techniques now available and surveying as many proteins as possible,
the overall genetic differences are remarkably small." (Gould S.J.,
"Ever Since Darwin", Penguin: London, 1977, p53)
In fact, the difference in protein amino acid sequences was only 0.8%
between chimp and human:
"In any case, the measurement of amino acid differences between
humans and living African great apes (gorillas and chimpanzees) led
to the most surprising result of all. We are virtually identical for
genes that have been studied, despite our pronounced morphological
divergence. The average difference in amino acid sequences between
humans and African apes is less than one percent (0.8 percent to be
precise)..." (Gould S.J., "Our Greatest Evolutionary Step", "The
Panda's Thumb", Penguin: London, 1980, p109).
That is, humans and chimps share more than 99% the same protein amino
acid sequences:
"Chimpanzees and we share more than 99 per cent of our genes."
(Dawkins R., "The Blind Watchmaker", Penguin: London, 1991, p263)
SC>Unfortunately, I do not know how such an estimation of genetic
>relatedness was made. The same questions John raised above, I also
>have. The problem, I beleive, lies in what is meant by "identity".
Indeed, this closeness of man and chimp raised a problem for
evolutionists:
"DNA in chimpanzees differs from our own by less than one per cent.
This worries geneticists, who would have expected a far bigger
difference to account for the enormous dissimilarity between the two
species... The genetic make-up of chimpanzees and humans is more
than 99 per cent identical, according to molecular biologists. It
seems to mean we had a common ancestor less than five or six million
years ago (see chapter eight), and is a puzzle to geneticists who
would have expected a bigger difference to account for the anatomical
dissimilarity" (Hitching F., "The Neck of the Giraffe: Where Darwin
Went Wrong", Ticknor & Fields: New York, 1982, p75,78)
It means that on this molecular biological basis, man and chimp are
one genus:
"DNA hybridization has shown how close genetically we and the African
great apes are. A recent systematic application of this relatively
new and fascinating technique (Sibley and Ahiquist, 1984) has shown
that humans and chimps are closer genetically than either is to the
gorilla and, in fact, even closer than two similar species of
gibbons. Or, for that matter, humans and chimps are more similar
than zebra and horse or goat and sheep." (Nelson H. & Jurmain R.,
"Introduction to Physical Anthropology", West Publishing Company:
St. Paul MN, Fifth Edition, 1991, p255)
Indeed, they would be sibling species:
"When two species scarcely differ in morphology but function as
separate and reproductively isolated populations in nature,
evolutionary biologists speak of "sibling species." Sibling species
generally display far fewer genetic differences than pairs of species
placed in the same genus but clearly different in morphology
("congeneric species")." (Gould S.J., "Ever Since Darwin", Penguin:
London, 1977, p53)
Indeed Gould points out that this is obviously not the case, and it
therefore calls into question the notion that organic traits are
controlled by single genes:
"Now chimps and humans are obviously not sibling species; we are not
even congeneric species by conventional taxonomic practice (chimps
belong to the genus Pan; we are Homo sapiens). But King and Wilson
have shown that the overall genetic distance between humans and
chimps is less than the average for sibling species and far less than
in any tested pair of congeneric species. A fine paradox, for
although I have argued strongly that our distinctions are matters of
degree only, we are still very different animals. If the overall
genetic distance is so small, then what has caused such a divergence
in form and behavior? Under the atomistic notion that each organic
trait is controlled by a single gene, we cannot reconcile our
anatomical dissimilarities with King and Wilson's findings, for many
differences in form and function would have to reflect many
differences in genes." (Gould S.J., "Ever Since Darwin", Penguin:
London, 1977, p53)
Johnson points out that though chimps and humans chemical "letters"
looks almost the same, the information content of the human genetic
system is must be significantly different from that of apes:
"Molecular studies have also produced claims having important
philosophical implications, particularly on the sensitive topic of
human evolution, because by some molecular measurements chimps
are much more similar to humans than they are to other non-human
primates. This degree of similarity may call the importance of
molecular comparisons into question, because it does little to
explain
the profound dissimilarities between humans and animals of any kind.
Evidently the information content of the human genetic system is
significantly different from that of apes, even though the
arrangement
of chemical "letters" looks almost the same. This point is lost on
some Darwinists." (Johnson P.E., "Darwin on Trial", InterVarsity
Press: Downers Grove Ill., Second Edition, 1993, p93)
Indeed, Gould points out that though the differences between man and
chimp at the genetic level might be minor, the *organisation* of that
genetic material at the chromosome level is major:
"The genetic differences between humans and chimps are minor,
but they include at least ten large inversions and translocations.
An inversion is, literally, the turning around of a chromosomal
segment. (Gould S.J., "Ever Since Darwin", Penguin: London, 1977,
p55)
Since even one such chromosome inversions would probably confer
sterility:
"The very small genetic distance between humans and chimps might
tempt us to try the most potentially interesting and ethically
unacceptable scientific experiment I can imagine-to hybridize our two
species and simply to ask the offspring what it is like to be, at
least in part, a chimpanzee. This interbreeding may well be
possible-so small are the genetic distances that separate us. But,
lest we fear the rise of a race comparable to the heroes in Planet of
the Apes, I hasten to add that the hybrids would almost certainly be
sterile-like a mule, and for the same reason....Each hybrid cell
would have a set of chimp and a corresponding set of human
chromosomes. Egg and sperm cells are made by a process called
meiosis, or reduction division. In meiosis, each chromosome must
pair (lie side by side) with its counterpart before cell division, so
that corresponding genes can match up one to one: that is, each
chimp chromosome must pair with its human counterpart. But if a
piece of human chromosome is inverted relative to its counterpart in
chimps, then gene-by-gene pairing cannot occur without elaborate
looping and twisting that usually precludes successful cell
division." (Gould S.J., "Ever Since Darwin", Penguin: London, 1977,
p55)
one might ask how did this chain of alleged descent from chimp-human
ancestor to human, manage to survive these major chromosomal
dislocations, each of which would render the link sterile?
God bless.
Steve
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