Out Of Africa Strikes Back

[Rokcet Scientist]

I still can't get by the selective "mass-extinction" of the Toba volcano which took out HSS but no one else.

Could've been a species-specific infectious disease (think: AIDS), that impacted HSS but not HE or HN?

[Digit]

I THINK you're wrong FT. Genetic variation has been calculated at 3%/Million yrs.
In a period of 1 million yrs the original parent group should be 3% different from their origins.
Meanwhile, back on the march, the same time period has elapsed for those who left the parent group, therefore they should be 3% different from their origins.
Same amount of diversity, the variation should have had different results between the 2 groups, but the number of variations should be the same.
The experts seem to be trying to get around this by saying the those who left Africa were reduced in number be 'bottlenecks'.
Why only those who left Africa?
Come back Charlie!

[FreeThinker]

Digit, you are forgetting the genetic diversity the parent group started with. That genetic diversity added to the ongoing accumulation of more genetic diversity would give the parent group the greatest diversity. Newer groups would only have the diversity that accumulated since they left the parent group and thus would have a smaller amount than the parent group.

We may disagree on this but we agree on one thing: Come back Charlie!

[Manystones]

Digit you need to do your homework on genetics...

There is a limited gene pool hence the lack of diversity as the descendants spread across the globe.

[Minimalist]

Hold the presses.....


A lone voice is crying out in the wilderness!


http://news.yahoo.com/s/livescience/200 ... RhJhFFeQoB

However, John Hawks of the University of Wisconsin-Madison says the paper is “mistaken.” A major flaw is that the current research is largely based on skull variability.


“You can’t find the origin of people by measuring the variability of their skulls,” Hawks told LiveScience.


Differences in skull features are related to genetics, and genetic variation depends on how much mixing occurs with other populations. “The main problem with the paper is that it takes some assumptions from genetics papers of 10 to 15 years ago that we now know are wrong,” Hawks said.

[Beagle]

http://johnhawks.net/weblog/reviews/ear ... ?seemore=y

It seems to me that the recent evolution of the face is mostly a consequence of selection on the dentition, which has evolved rapidly in the last 15,000 years throughout the world. That has little, if anything, to do with modern human origins.

The entire John Hawks response.

[Digit]

MS and FT, if you check back you'll find that I hold my hand up to being ignorant on genetics. My argument is based on logic.
Surely, whatever genetic diversity the parent group has those leaving will carry with them, if not how do they lose it?
Fast forward 1000000yrs, if diversity is measured as 3%/million yrs then both groups will have genentically changed 3%. If not, how not?

[FreeThinker]

Digit, hang in with me here on this, I think I can clarify what I am saying.

When a small group leaves a large parent population, its genetic diversity will be less than the parent group as a whole. This is because not every genetic type contained in the parent group as a whole will be represented in the smaller splinter group as it breaks off from the parent group. Once the smaller group breaks off from the larger parent group you essentially have two groups, one large with lots of genetic variance, and one smaller with not so much genetic diversity (consider too that a group splitting off, especially in those ancient "tribal" times would probably been of the same "tribe" and thus would most likely have individuals who had very similar genetics). This is why the genetic diversity of the parent group always will be ahead of the splinter group.

[Forum Monk]

I am not sure if I complete follow this myself, F/T.
This discussion depends on the definition of genetic diverstity. For example, if I take a popluation of objects which are made up of 200 different colors, that is, each individual is one of 200 unique colors, and then separate a random subgroup, clearly the number of colors in the subgroup will be less than than the number in the larger group. Now of course this depends on several factors:
1 - how the diversity of individuals is expressed
2 - how the diversity is measured i.e. number of unique variants
3 - the size of the respective populations

It seems, therefore the individuals within the subgroup remain as diverse from one and another as those in the larger group, but the probabilities of of a certain color to exist is now different because the population size changes.

[Digit]

Yep FT, I'd worked along those lines as well, then I found a snag.
We are discussing hunter/gatherers here, and the experts tell me the ideal size for such a group is 30 individuals. Obviously, before group fission takes place, that number is likely to be higher.
The group splits, and for the sake of argument let's say the new group consists of 10 individuals, your statement now applies. But only if no contact is maintained with other groups that have also split from the parent group.
Most societies maintain strict rules to prevent inbreeding, so contact with others would be necessary, also leaving the parent group, and marching off into the wide blue yonder severs family ties, therefore I suspect our H/Gs would only move that distance necessary for living.
But I will repeat that the original artical can only offer unspecified 'bottlenecks' as the method of reducing diversity, not dispersion.
I'd like to your views on that idea as well.

[Starflower]

Thank you to everyone, you have pretty much addressed all of my 'yes but's'. Keep up the good work.

Star