Re: What makes us human?

On Mon, 14 Aug 2006 16:27:59 -0400, r norman
<NotMyRealEmail@xxxxxxxxxxxx> wrote:

On 14 Aug 2006 10:44:35 -0700, "rev.goetz" <jimgoetz316@xxxxxxxxx>
wrote:


Jenny Brien wrote:
From a Daily Telegraph article of the same name

http://www.telegraph.co.uk/connected/main.jhtml?xml=/connected/2006/08/01/echuman01.xml&page=4

<quote>
Chimps and humans each have about three billion nucleotides in their
genomes - 99 per cent of those may be identical, but that still leaves
about 30 million differences. Most of those are unimportant, the
background noise of genomic evolution. But some matter: which?

Therein lies the importance of microcephaly. The discovery of genes
that control the growth of the brain immediately suggested that these
genes might also have changed in the last six million years since we
last shared an ancestor with chimps. And so it proved: of the four
microcephaly genes that have been found, three bear the hallmarks of
rapid evolution. To be sure, chimps have versions of these genes, but
the human version is different. So different, in fact, that their
evolution must have been driven by natural selection.

</quote>

O.K. As a lay person I can understand that. Natural selection
preserves favourable mutations. "Favourable" for humans includes bigger
brains, so the genes which affect that are going to change more than
other genes, simply because favourable mutations are passed down to
future generations.

What I don't yet understand is this: I watched the program of the same
name on Channel 4, on which the author of the article, Dr Armand Leroi,
of Imperial College London, said that a particular mutation on one of
these genes first appeared after the invention of agriculture. Is that
simply a hypothesis, or is it indeed possible to date the first
appearance of a mutation so precisely and what is the thinking behind
it?

He obviously discovered the agriculture gene. I am impressed.


An analysis of two genes associated with brain development,
Microcephalin and ASPM show relatively recent changes between
haplotypes and haplogroups. A Microcephalin haplogroup appears to
have originated some 37,000 years ago and an ASPM haplogroup some 5800
years ago. A relatively non-technical discussion is at
http://www.hhmi.org/news/lahn4.html
Microcephalin and ASPM showed significant changes under the pressure of natural selection during the making of the human species.
Note: that is just the most recent variation of the genes. It does
not indicate that the brain took a large (or even a small) leap in
size at those times. Those changes occured way back, at the origins
of the human line.



I thought human intelligence was related to cortex not brain growth.

Quote from "lahn4.html" link above:

"Microcephalin and ASPM showed significant changes under the pressure
of natural selection during the making of the human species."

"under the 'pressure' of natural selection"? Does NS now have
"purpose"? I thought NS merely was recognition that a random mutation
had survived better than its predecessor. What 'pressure'?

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