millions of years?

The problem is that it is locus dependent i.e. you see a different pattern if you look at mtDNA versus nuclear. And there is among locus variation i.e. some show signs of bottlenecks and others don't. Some cases could be a result of selection i.e. a recent selective sweep of a specific chromosomal region whereas others could suggest a bottleneck. As to the dates, I would have to look it up since I have not really kept up much with the human evolution literature so much.

What would be the difference (in the data) if a region
just hadn't changed compared to a bottle-neck?

Good question. Actually, in most population genetics studies, one looks at highly variable loci that are neutral i.e. microsatellites. If you look at a lot of such loci in multiple individuals and they are all identical, that goes against the expectation for such loci and one could conclude that something had decreased variation in the population i.e. bottleneck/founder event. Similarly one can sequence the Dloop of the mitochondrial genome which has a fast evolutionary tempo. You and I probably differ in our Dloop...if you sequenced squirrels (since these seem to be the favorite animal on the forum ) from lots of different localities and they are all identical or nearly so one can again posit a bottleneck. From my own research it is historically known that muskoxen underwent multiple bottnecks and they are extremely homogeneous in mtDNA sequences and microsatellite in contrast to bovids (though things get interesting when you look at ancient samples...tune in for that when I publish it soon The above examples are different from say a highly conserved protein or protein domain where the rest of the genome could be quite variable but the one locus is highly conserved indicating it is under selection...in some cases you can test this with knockout experiments which are done in mice and see if there is a mutation...or if you get offspring at all.

That makes sense, thanks.Who has been talking about squirrels? In the UK we have lost
our reds due to the selective advantage that greys have ...

I was surprised to see that last time I was in England...the squirrels looked like the ones I was used to seeing in New York. In Munich there are red and black squirrels and they have long hair on their ears that make it look like they have wings on their heads...pretty dopey looking animals actually..in the Nature of Mutations II thread squirrels came up as an example...

Scotland and a few places in England still have the "native" red squirrels. American grey squirrels are far more common in the UK (and there are some black-furred individuals of that species around).

Hi PaulK
When did the American squirrels arrive in England? In the places where the red squirrels live, are there also grey squirrels or do they exclude one another?...It's sort of reverse colonialism..the UK colonizes America and the American squirrels invade the UK

The American ones have been displacing the reds for
quite some time now ... who said the cold-war was over

guess it sucks to be a red squirrel

I had to look it up, but the greys were introduced in the period from 1876 to 1929 according to this site Page Not Found | About | The University of AberdeenWhy ? I have no idea.Nobody seems to know exactly why the reds don't survive alongside the greys either. But they usually don't. Either they leave or they die out (don't ask me which).As this story demonstrates the greys can be very aggressive:
BBC NEWS | UK | England | Granddad guns down terror squirrel[This message has been edited by PaulK, 07-08-2003]

I think I read somewhere that grey squirrels are larger
and more agressive ... not sure either though. Maybe they
come out of hibernation earlier 'cause their ancestors lived
in more extreme climates that the temperate UK.

Grey squirrels are heavier built (they're shorter in length but weigh more) and they're bolder than the reds. But how they actually interact is a bit of a mystery.

Hi PaulK,
Interesting site about the introduction of grey squirrels to the UK. What I find interesting is they are not aggressive towards one another and no obvious disease was transmitted from grey to red. The article postulates competition for resources which I guess is plausible..though how much resources do squirrels require? It could be tested if there is a decline in preferred food availablity for red squirrels upon introduction of greys. Can grey and red form hybrids? Even infertile F1's?If the greys keep biting people on the face leading to geriatric vigilantism...perhaps the House of Lords in considering a fox hunting ban could merely re-direct the hunt to grey squirrels? Perhaps the event would lose some of its rustic charm but it might be a better sell as environmentally sound

...and watching the hounds try to climb a tree might be fun

Then I'd go look to hibernation behaviour.Isn't it more or less a north-south divide?If the southern red squirrels were used to lying in bed
until, say early april while the greys get up
in early march it'd sure make a difference to population numbers
(I would have thought) ... anyhow wild conjecture on my part
and I apologise[After thought: Perhaps we need Syamsu to analyse them from
the PoV of environmental interactions that contribute to
reproduction .... ][This message has been edited by Peter, 07-09-2003]