On Fri, 24 Sep 1999 00:56:29 -0500 (CDT), Wesley R. Elsberry wrote:
[...]
>SJ>regarding the possibility that humans may have *twice* as
>>many genes (140,000) as previously thought
>>(60,000-80,000). If this holds up it makes the `humans
>>share 98% of their genes with chimps' line even more shaky
>>(unless of course chimps turn out to have twice as many
>>genes as first thought too!).
WE>The 98% figure given by Stephen comes from DNA hybridization
>studies, and is *not* "98% of genes", but should rather be
>"98% of DNA".
First, King & Wilson's 1975 study did not only use DNA hybridization, but
also protein immune reactions:
"Moving on from immune reactions to proteins to the DNA itself, which
orders the shape of the proteins, Wilson and another student, Marie-Claire
King, showed that chimp and man are 99 per cent identical." (King M.-C.
& Wilson A.C., 'Evolution at two levels in humans and chimpanzees",
Science, 188:107-116, 1975). (Gribbin J. & Cherfas J., "The Monkey
Puzzle: A Family Tree", 1982, p30)
"...in 1975 Allan Wilson used all the information he had to calculate the
average difference between the species. Thirteen proteins, ranging in size
from 30 to 650 amino acids long, differed by a total of about 19 amino
acids. Averaged over the entire 2633 amino acids that works out to 7.2
differences per 1000 amino acids: the proteins of man and chimp are more
than 99 per cent the same." (King M-C. & Wilson A.C., "Evolution at two
levels in humans and chimpanzees", Science, 188: 107-116, 1975) (Gribbin
J. & Cherfas J., 1982, p117)
Second, King and Wilson did infer from the high degree of similarity
between those proteins and DNA studied of humans and chimps that there
was a corresponding hight degree of similarity between their genes:
"Soon after the expansion of molecular biology in the 1950's, it became
evident that by comparing the proteins and nucleic acids of one species
with those of another, one could hope to obtain a quantitative and
objective estimate of the "genetic distance" between species. Until then,
there was no common yardstick for measuring the degree of genetic
difference among species. The characters used to distinguish among
bacterial species, for example, were entirely different from those used for
distinguishing among mammals. The hope was to use molecular biology to
measure the differences in the DNA base sequences of various species. This
would be the common yardstick for studies of organismal diversity.
During the past decade, many workers have participated in the
development and application of biochemical methods for estimating genetic
distance. Those methods include the comparison of proteins by
electrophoretic, immunological, and sequencing techniques, as well as the
comparison of nucleic acids by annealing techniques. The only two species
which have been compared by all of these methods are chimpanzees (Pan
troglodytes) and humans (Homo sapiens). This pair of species is also
unique because of the thoroughness with which they have been compared
at the organismal level-that is, at the level of anatomy, physiology,
behavior, and ecology. A good opportunity is therefore presented for
finding out whether the molecular and organismal estimates of distance
agree.
The intriguing result, documented in this article, is that all the biochemical
methods agree in showing that the genetic distance between humans and
the chimpanzee is probably too small to account for their substantial
organismal differences.
Indications of such a paradox already existed long ago. By 1963, it
appeared that some of the blood proteins of humans were virtually identical
in amino acid sequence with those of apes such as the chimpanzee or
gorilla (1). In the intervening years, comparisons between humans and
chimpanzees were made with many additional proteins and with DNA.
These results, reported herein, are consistent with the early results.
Moreover, they tell us that the genes of the human and the chimpanzee are
as similar as those of sibling species of other organisms (2). So, the
paradox remains. In order to explain how species which have such similar
genes can differ so substantially in anatomy and way of life, we review
evidence concerning the molecular basis of evolution at the organisms
level. We suggest that evolutionary changes in anatomy and way of life are
more often based on changes in the mechanisms controlling the expression
of genes than on sequence changes in proteins. We therefore propose that
regulatory mutations account for the major biological differences between
humans and chimpanzees.
Similarity of Human and Chimpanzee Genes
To compare human and chimpanzee genes, one compares either
homologous proteins or nucleic acids. At the protein level, one way of
measuring the degree of genetic similarity of two taxa is to determine the
average number of amino acid differences between homologous
polypeptides from each population. The most direct method for
determining this difference is to compare the amino acid sequences of the
homologous proteins. A second method is microcomplement fixation,
which provides immunological distances linearly correlated with amino acid
sequence difference. A third method is electrophoresis, which is useful in
analyzing taxa sufficiently closely related that they share many alleles. For
the human-chimpanzee comparison all three methods are appropriate, and
thus many human and chimpanzee proteins have now been compared by
each method. We can therefore estimate the degree of genetic similarity
between humans and chimpanzees by each of these techniques."
(King M.-C. & Wilson A.C., "Evolution at Two Levels in Humans and
Chimpanzees", Science, 11 April 1975, Vol. 188, No. 4184, p107)
Third, the "98% figure" is often used of "genes" not "DNA" in the
scientific literature:
"Additional evidence that changes in structural genes may not be correlated
with anatomical evolution was recently reported by Mary-Claire King of
the University of California at San Francisco and Wilson. They compared a
group of 44 proteins of human beings and chimpanzees- two species so
dissimilar that they are placed by taxonomists in different families.
However, King and Wilson found that the human proteins are, on the
average, 99 percent identical to those of the chimpanzees. This means that
the structural genes coding for these 44 proteins are as similar as the
structural genes of species classified as sibling species." (Kolata G.B.,
"Evolution of DNA: Changes in Gene Regulation," Science, Vol. 189, 8
August 1975, p446)
"More recently, molecular biologists have revealed that our genes are
about 98 percent the same as those of an African ape." (Shreeve J., "The
Neandertal Enigma: Solving the Mystery of Modern Human Origins,"
[1995], William Morrow & Co: New York, 1996, pp22-23).
"Although humans may look entirely different from chimpanzees and
gorillas, those differences are superficial. Where it counts-in their genes-all
three are ninety-nine percent identical." (Edey M.A. & Johanson D.C.,
"Blueprints: Solving The Mystery of Evolution", 1989, p363).
"In all the cases that I have discussed so far, anatomical evidence of
relationships was already convincing, and the DNA-based conclusions
confirmed what the anatomists had already concluded. But DNA was also
able to resolve the problem at which anatomy had failed - the relationships
between humans, gorillas, and chimpanzees. As the figure on page 17
shows, humans differ from both common chimps and pygmy chimps in
about 1.6% of their (our) DNA, and share 98.4%. Gorillas differ somewhat
more, by about 2.3%, from us and from both of the chimps...The genetic
distance (1.6%) separating us from pygmy or common chimps is barely
double that separating pygmy from common chimps (0.7%)...The
remaining 98.4% of our genes are just normal chimp genes....In this respect
as in most others, we are just a third species of chimpanzee..." (Diamond
J., "The Rise and Fall of the Third Chimpanzee", Vintage: London, 1992,
p18).
WE>The number of genes/loci comes from genomic
>sequencing studies. Stephen is invited to explain why anyone
>would expect the number of loci found via genomic sequencing
>to alter our opinion of the confidence with which to hold the
>DNA hybridization result.
I already said "why". "If humans have The have *twice* as many genes
(140,000) as previously thought (60,000-80,000)" and "unless of course
chimps turn out to have twice as many genes as first thought too", then the
statement that `humans share 98% of their genes with chimps' will be
wrong. Humans and chimps might share 98% of their *known* genes,
but that does not necessarily mean that they share 98% of their total
genes.
The problem with the assumption that humans share 98% of their genes
was that: a) it was based on only a limited number of proteins and
fragments of DNA; b) those fragments of human DNA that did not closely
match that of chimps were discarded; and c) as King and Wilson pointed
out, their study only compared structural genes. There might be major
differences in regulatory genes:
"The intriguing result, documented in this article, is that all the biochemical
methods agree in showing that the genetic distance between humans and
the chimpanzee is probably too small to account for their substantial
organismal differences. Indications of such a paradox already existed long
ago. By 1963, it appeared that some of the blood proteins of humans were
virtually identical in amino acid sequence with those of apes such as the
chimpanzee or gorilla (1). In the intervening years, comparisons between
humans and chimpanzees were made with many additional proteins and
with DNA. These results, reported herein, are consistent with the early
results. Moreover, they tell us that the genes of the human and the
chimpanzee are as similar as those of sibling species of other organisms (2).
So, the paradox remains. In order to explain how species which have such
similar genes can differ so substantially in anatomy and way of life, we
review evidence concerning the molecular basis of evolution at the
organisms level. We suggest that evolutionary changes in anatomy and way
of life are more often based on changes in the mechanisms controlling the
expression of genes than on sequence changes in proteins. We therefore
propose that regulatory mutations account for the major biological
differences between humans and chimpanzees." (King M.-C. & Wilson
A.C., "Evolution at Two Levels in Humans and Chimpanzees", Science, 11
April 1975, Vol. 188, No. 4184, p107)
[...]
WE>An interesting-sounding paper was mentioned on t.o. recently.
>
>Jorge J. Yunis and Om Prakash. "The Origin of Man: A
>Chromosomal Pictorial Legacy", in Science, Vol. 215, 19 Mar
>1982, p.1525-1530.
>
>I haven't had a chance to see this one myself yet. This is
>said to look at the banding patterns of chromosomes in
>primates. The relationships in banding patterns between the
>various species examined are said to provide striking evidence
>of similarities between the various species, and where
>differences occur, one can see that the explanation of
>inversion of chromosomal sections can cover much of the
>apparent variation.
It is indeed an interesting paper. Glenn had previously mentioned it
and I had posted something on it some time ago. Its Figure 3 explains it
all:
---------------------------------------------------------------
Human
18
2
|
1
|
Chimpanzee 17-18-15-12-9-5-4---|
9 Human-chimpanzee
7 progenitor
2p
|
Gorilla 17-18-14-12-10-8-5-4-1-|
Y
|
X
22
21
20
19
18
17
16
15
14
13
12
11
Orangutan 20 10
\ 9
17 8
\ 7
11 6 Hominid
\ 5 ancestor
8 4
\ 3
4 2q
\ 2p
2q 1
\ |
\|
Hominid-orang 3-7-10--17--Y--|
precursor
Fig. 3. Presumed ancestors of man, chimpanzee, gorilla, and
orangutan. In the middle are illustrated the chromosomes of a
presumed hominoid ancestor whose chromosomes were largely similar to
those of human (H) and to a great extent to chimpanzee (C), gorilla
(G), and orangutan (O). Before the divergence of man and chimpanzee
took place, their ancestor shared similar chromosomes 2p, 7, and 9
(human- chimpanzee ancestor). Man then diverged by fusion of
chromosomes 2p and 2q into chromosome 2 and by a small pericentric
inversion in chromosomes 1 and 18. By contrast, seven and nine major
nonheterochromatic changes in individual chromosomes occurred in
chimpanzee and gorilla, respectively. A presumed precursor of the
hominoid ancestor and orangutan had the same chromosomes as the
hominoid ancestor except for chromosomes 3, 7 10, and Y, which were
similar to those of orangutan, and chromosome 17, which was like that
of rhesus (R) and baboon (B). From this precursor, orangutan
diverged with changes in chromosomes 2q, 4, 8, 11, 17, and 20.
[...]
(Yunis J.J. & Prakash O., "The Origin of Man: A Chromosomal Pictorial
Legacy," Science, Vol. 215, No. 4539, March 1982, p1528)
---------------------------------------------------------------
Personally I find the above compelling evidence that humans shared a
common ancestor with chimps. But I don't find the evidence similarly
compelling that it all happened solely by Darwinian evolution, or indeed
any fully naturalistic evolutionary process, (although I would have no
problem if it did).
But in the absence of a equally compelling naturalistic information-
generating mechanism, my Progressive Mediate Creation model
hypothesis is that *all* the major increases in genetic information (ie.
new designs), in not just man, but all living things, going back to the
origin of life from non-living chemicals, came about primarily by an
Intelligent Designer supernaturally modifying and/or adding to existing
genetic information:
"Suppose contemporary evolutionary theory had blind chance built into it
so firmly that there was simply no way of reconciling it with any sort of
divine guidance. It would still be perfectly possible for theists to reject that
theory of evolution and accept instead a theory according to which natural
processes and laws drove most of evolution, but God on occasion abridged
those laws and inserted some crucial mutation into the course of events.
Even were God to intervene directly to suspend natural law and inject
essential new genetic material at various points in order to facilitate the
emergence of new traits and, eventually, new species, that miraculous and
deliberate divine intervention would by itself leave unchallenged such key
theses of evolutionary theory as that all species derive ultimately from some
common ancestor. Descent with genetic intervention is still descent-it is
just descent with nonnatural elements in the process." (Ratzsch D.L., "The
Battle of Beginnings", 1996, pp187-188)
Steve
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"It is perhaps clear to the reader that the genetic system is, in principle,
isomorphic with communication systems designed by communications
engineers. As a matter of fact, genetical systems have historical priority
since organisms have been using the principles of information theory and
coding theory for at least 3.8 x 10^9 years!" (Yockey H.P., "Information
Theory and Molecular Biology", Cambridge University Press: Cambridge
UK, 1992, p7)
Stephen E. Jones | sejones@iinet.net.au | http://www.iinet.net.au/~sejones
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