http://news.bbc.co.uk/1/hi/sci/tech/7358868.stm

"Ancient humans started down the path of evolving into two separate
species before merging back into a single population, a genetic study
suggests."

Interesting. This is I presume the source of the oft quoted "There is more
racial diversity inside Africa than outside"?

Mark

--

On Apr 25, 4:01 pm, Mark.Wri...@bristol.ac.uk wrote:
> http://news.bbc.co.uk/1/hi/sci/tech/7358868.stm
>
> "Ancient humans started down the path of evolving into two separate
> species before merging back into a single population, a genetic study
> suggests."
>
> Interesting. This is I presume the source of the oft quoted "There is more> racial diversity inside Africa than outside"?
>
> Mark
>
> --

Interesting but not, I suspect, the source of the racial diversity
quote.

The racial diversity quote just acknowledges that the group who left
africa were a small subset of teh original population, and so they
must have contained less diversity when they left than the original
stay at home population.

Lance

Lance  wrote:
: Interesting but not, I suspect, the source of the racial diversity
: quote.

: The racial diversity quote just acknowledges that the group who left
: africa were a small subset of teh original population, and so they
: must have contained less diversity when they left than the original
: stay at home population.

That's true, but that would preclude there currently being more diversity
outside Africa, on account of there having been much more natural
selection in a larger population?
Mark

--

On Apr 29, 7:09 pm, Mark.Wri...@bristol.ac.uk wrote:
> Lance  wrote:
>
> : Interesting but not, I suspect, the source of the racial diversity
> : quote.
>
> : The racial diversity quote just acknowledges that the group who left
> : africa were a small subset of teh original population, and so they
> : must have contained less diversity when they left than the original
> : stay at home population.
>
> That's true, but that would preclude there currently being more diversity
> outside Africa, on account of there having been much more natural
> selection in a larger population?
> Mark
>
> --

Since I am so deeply ignorant and can't speak with authority on the
issue I will compromise by asking as David Smithian type question: Do
you think the time involved since the two groups (the first going to
Australia, the second forming the remainder of modern humanity outside
Africa) left Africa is great enough for significant genetic change to
occur?

Lance

On Apr 30, 1:12 pm, Lance  wrote:
> On Apr 29, 7:09 pm, Mark.Wri...@bristol.ac.uk wrote:
>
>
>
> > Lance  wrote:
>
> > : Interesting but not, I suspect, the source of the racial diversity
> > : quote.
>
> > : The racial diversity quote just acknowledges that the group who left
> > : africa were a small subset of teh original population, and so they
> > : must have contained less diversity when they left than the original
> > : stay at home population.
>
> > That's true, but that would preclude there currently being more diversity
> > outside Africa, on account of there having been much more natural
> > selection in a larger population?
> > Mark
>
> > --
>
> Since I am so deeply ignorant and can't speak with authority on the
> issue I will compromise by asking as David Smithian type question: Do
> you think the time involved since the two groups (the first going to
> Australia, the second forming the remainder of modern humanity outside
> Africa) left Africa is great enough for significant genetic change to
> occur?
>
Certainly. Look at the fox -> dog experiment in Russia that we
discussed here recently the change took only a few decades (a dozen or
so generations) and was a very marked difference.

The size of the population matters only if the size results in a
greater exposure to evolutionary pressure. If you have two
populations, one tiny and one huge, but the huge population is in a
homogeneous environment, and the tiny one spread over many different
environments, then you'd expect more diversity in the tiny population.
If they're both in similarly challenging environments, then, indeed,
there'd be more diversity in the larger population. So the remark
about larger populations being more diverse conceals a hidden
assumption.

On May 1, 8:45 am, verity.bro...@gmail.com wrote:
> On Apr 30, 1:12 pm, Lance  wrote:
>
>
>
> > On Apr 29, 7:09 pm, Mark.Wri...@bristol.ac.uk wrote:
>
> > > Lance  wrote:
>
> > > : Interesting but not, I suspect, the source of the racial diversity
> > > : quote.
>
> > > : The racial diversity quote just acknowledges that the group who left> > > : africa were a small subset of teh original population, and so they
> > > : must have contained less diversity when they left than the original
> > > : stay at home population.
>
> > > That's true, but that would preclude there currently being more diversity
> > > outside Africa, on account of there having been much more natural
> > > selection in a larger population?
> > > Mark
>
> > > --
>
> > Since I am so deeply ignorant and can't speak with authority on the
> > issue I will compromise by asking as David Smithian type question: Do
> > you think the time involved since the two groups (the first going to
> > Australia, the second forming the remainder of modern humanity outside
> > Africa) left Africa is great enough for significant genetic change to
> > occur?
>
> Certainly. Look at the fox -> dog experiment in Russia that we
> discussed here recently the change took only a few decades (a dozen or
> so generations) and was a very marked difference.
>
> The size of the population matters only if the size results in a
> greater exposure to evolutionary pressure. If you have two
> populations, one tiny and one huge, but the huge population is in a
> homogeneous environment, and the tiny one spread over many different
> environments, then you'd expect more diversity in the tiny population.
> If they're both in similarly challenging environments, then, indeed,
> there'd be more diversity in the larger population. So the remark
> about larger populations being more diverse conceals a hidden
> assumption.- Hide quoted text -
>
> - Show quoted text -

I think there is a certain amount of genetic change that takes place
just with the passage of time. This change is not (at least I think it
is not) related to evolutionary pressure. This natural change is
(again I think) used to estimate the time a since divergence between
groups, etc.

Small genetic changes can produce large changes in the phenotype. I
don't think you can estimate genetic change simply by looking at
phenotypes. Again, I speak subject to correction.

I think large interbreeding populations are more resistant to genetic
change than small ones. So small groups that splinter off and enter
new environments may show greater change. But it would be change
within a relative homogenous set of genes...

Lance

On May 1, 1:58 pm, Lance  wrote:
>
>
> I think there is a certain amount of genetic change that takes place
> just with the passage of time. This change is not (at least I think it
> is not) related to evolutionary pressure. This natural change is
> (again I think) used to estimate the time a since divergence between
> groups, etc.
>
Yes, I agree, of course, that time is a factor! This change is related
to evolutionary pressure - over time there mutations creep in, the
longer you have, the more there are (being a pilot, living in a
granite house, and so forth increase the chances, as would eating
certain things). Whether these mutations are incorporated in the
genome (rather than, as is usually the case, resulting in abortion or
other non-survival to reproductive age) depends on whether they are
dangerous or not, if not they are more likely to survive. If they are
positively useful then there might even be speciation based on them.
So, in short, even these rely on evolutionary pressure for their
continuance.

Genetic material that doesn't go through meiosis like the
mitochondrial DNA and the X chromosome will gather changes over time
and have, as you say, been used to calculate time of population
diversion.
>
> Small genetic changes can produce large changes in the phenotype. I
> don't think you can estimate genetic change simply by looking at
> phenotypes. Again, I speak subject to correction.
>
> I think large interbreeding populations are more resistant to genetic
> change than small ones. So small groups that splinter off and enter
> new environments may show greater change. But it would be change
> within a relative homogenous set of genes...
>
It probably depends a bit on what we are thinking of as 'large' and
'small'! In the case of very small, certainly there isn't going to be
a large variation - I liked an example that came up this week:

http://www.thisiswesterndailypress.co.uk/displayNode.jsp?nodeId=145786&command=displayContent&sourceNode=231644&home=yes&more_nodeId1=145795&contentPK=20508448&bustcache=