"RFoy H"  wrote in message
> Recently I read an article about the Y Chromosome. It suggested
> that, though small compared to the x, it covers a lot of territory.
>
The testis-determining factor, at the tip of the Y chromosome, has very
far-reaching effects, changing a body from female to male. However it acts
like a switch. The genes that build the penis, for example, probably are not
on the Y chromosome at all.
>
> It also said that it evolves rather rapidly. I haven't a clue what that
> really means.
>
What it means is that when you compare a Y chromosome with one from several
hundred thousand years ago, there will be more differences than if you
compare two autosomes. You could test this by comparing sequence homology in
humans and chimpanzees.
>
> As a result of the rapid evolution of the Y chromosome, would it
> not be possible for males to have evolved to fill different niches
> within a small scale tribal social group?
>
> Is this reasonable?
>
Estimate the chimp-human split from Y-independent data. This then tells you
how fast the Y-chromosome is evolving. If we assume a date of 5 million
years, we can calibrate the Y clock. Looking at human sequences, this gives
us a date for Y "Adam". By looking at other known human splits,
for instance
the colonisation of the Americas, we can get further calibration.
What you will find is that Y Adam lived quite recently, and that many
sub-populations also have one or maybe a handful of male founders. It is
therefore not plausible that there is much maintenance of different Y
chromosomes by frequency-dependent selection (i.e. one haplotype makes men
good arrow-makers whilst another codes for witch-doctors. The only
witch-doctor in a tribe is highly fit whilst if you have ten witch-doctors
eight will starve, and the same for arrow-makers, so both are maintained.)
This is not to say that this effect never happens, anywhere, but not on a
large scale.
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