----- Original Message -----
From: "Ian Pitchford" 
To: 
Sent: Friday, December 19, 2003 9:26 AM
Subject: [evol-psych] Lifestyle accounts for difference in chimp, human
genome


> DNA analysis for chimpanzees and humans reveals striking differences in
genes
> for smell, metabolism and hearing
> FOR RELEASE: Dec. 18, 2003
> Contact: Roger Segelken
> Office: 607-255-9736
> E-Mail: hrs2{at}cornell.edu
>
> ITHACA, N.Y. -- Nearly 99 percent alike in genetic makeup, chimpanzees and
> humans might be even more similar were it not for what researchers call
> "lifestyle" changes in the 6 million years that separate us
from a common
> ancestor. Specifically, two key differences are how humans and chimps
perceive
> smells and what we eat.
>
> A massive gene-comparison project involving two Cornell University
scientists,
> and reported in the latest issue of the journal Science (Dec. 12, 2003),
found
> these and many other differences in a search for evidence of accelerated
> evolution and positive selection in the genetic history of humans and
chimps.
>
> In the most comprehensive comparison to date of the genetic differences
between
> two primates, the genomic analysts found evidence of positive selection in
> genes involved in olfaction, or the ability to sense and process
information
> about odors. "Human and chimpanzee sequences are so similar, we were not
sure
> that this kind of analysis would be informative," says evolutionary
geneticist
> Andrew G. Clark, Cornell professor of molecular biology and genetics. "But
we
> found hundreds of genes showing a pattern of sequence change consistent
with
> adaptive evolution occurring in human ancestors." Those genes are involved
in
> the sense of smell, in digestion, in long-bone growth, in hairiness and in
> hearing. "It is a treasure-trove of ideas to test by more careful
comparison of
> human and chimpanzee development and physiology," Clark says.
>
> The DNA sequencing of the chimpanzee was performed by Celera Genomics, in
> Rockville, Md., as part of a larger study of human variation headed by
company
> researchers Michele Cargill and Mark Adams.
>
> Celera generated some 18 million DNA sequence "reads," or
about two-thirds
as
> many as were required for the first sequencing of the human genome.
Statistical
> modeling and computation was done by Clark and by Rasmus Nielsen, a
Cornell
> assistant professor of biological statistics and computational biology.
Some of
> the analysis, which also compared the mouse genome, used the supercomputer
> cluster at the Cornell Theory Center. Clark explains, "By lining up the
human
> and chimpanzee gene sequences with those of the mouse, we thought we might
be
> able to find genes that are evolving especially quickly in humans. In a
sense,
> this method asks: What are the genes that make us human? Or rather, what
genes
> were selected by natural selection to result in differences between humans
and
> chimps?" The study started with almost 23,000 genes, but this number fell
to
> 7,645 because of the need to be sure that the right human, chimp and mouse
> genes were aligned.
>
> According to Clark, all mammals have an extensive repertoire of olfactory
> receptors, genes that allow specific recognition of the smell of different
> substances. "The signature of positive selection is very strong in both
humans
> and chimps for tuning the sense of smell, probably because of its
importance in
> finding food and perhaps mates," says Clark. In addition to the great
departure
> in smell perception, differences in amino acid metabolism also seem to
affect
> chimps' and humans' abilities to digest dietary protein and could date
back to
> the time when early humans began eating more meat, Clark speculates.
> Anthropologists believe that this occurred around 2 million years ago, in
> concert with a major climate change.
>
> "This study also gives tantalizing clues to an even more complex
difference --
> the ability to speak and understand language," Clark says.
"Perhaps some
of the
> genes that enable humans to understand speech work not only in the brain,
but
> also are involved in hearing." Evidence for this came from a particularly
> strong sign of selection acting on the gene that codes for an obscure
protein
> in the tectorial membrane of the inner ear. One form of congenital
deafness in
>
> humans is caused by mutations to this gene, called alpha tectorin.
>
> Mutations in alpha tectorin result in poor frequency response of the ear,
> making it hard to understand speech. "It's something like replacing the
> soundboard of a Stradivarius violin with a piece of plywood," Clark notes.
The
> large divergence between humans and chimps in alpha tectorin, he says,
could
> imply that humans needed to tune the protein for specific attributes of
their
> sense of hearing. This leads Clark to wonder whether one of the
difficulties in
> training chimpanzees to understand human speech is that their hearing is
not
> quite up to the task. Although studies of chimpanzee hearing have been
done,
> detailed tests of their transient response have not been carried out.
>
> Clark emphasizes that a study like this cannot prove that the biology of
humans
> and chimps differ because of this or that particular gene. "But it
generates
> many hypotheses that can be tested to yield insight into exactly why only
1
> percent in DNA sequence difference makes us such different beasts," he
says.
>
> Also collaborating in the study were researchers at Applied Biosystems
(Foster
> City, Calif.), Celera Diagnostics (Alameda, Calif.) and Case Western
Reserve
> University in Cleveland. The Science report is titled, "Inferring
non-neutral
> evolution from human-chimp-mouse orthologous gene trios."
>
> http://www.news.cornell.edu/releases/Dec03/chimp.life.hrs.html
>
>
>
>
> Human Nature Review http://human-nature.com
> Evolutionary Psychology http://human-nature.com/ep
> Human Nature Daily Review http://human-nature.com/nibbs
>
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