Toba volcano eruptions - 1.000 - 10,000 breeding pairsunb

[Murdstone]

I was at the Smithsonian last year. They had a wonderful exhibit on human evolution. One of the displays mentioned the Toba eruption 75,000 years ago and how after that we were left with 1,000 - 10,000 human breeding pairs.

How is this estimate being made? Is there also some information on pop distribution geographically of these 1,000 - 10,000 breeding pairs?

Thanks

 

[Skrambles]

The theory is based on genetic analysis suggesting there was a population bottleneck around the same time as the eruption. I've never heard of any definitive archaeological evidence for this theory though.

 

[Murdstone]

I found this link - http://www.physorg.com/news183278038.html

I have heard the stuff before about the Alu markers. It's amazing what they can do with 2 samples.

The article starts out - "Modern humans are known to have less genetic variation than other living primates"

Someone in the comments made an interesting observation - "I wonder why these disasters endangered humans, lowering our genetic diversity, but didn't do the same to most other animals.." (especially other primates??)

I have no answer.

 

[Skrambles]

Just because those species have more genetic variation than humans does not mean they did not also go through a bottleneck. If those populations were already more diverse going into a bottleneck then it makes sense they would also be more diverse when the population rebounded.

 

[Murdstone]

While your explanation provides a plausible answer, the tone of the article seems to suggest that the difference in genetic variation found between other primates and humans is unusual. Meaning at one time they were thought to be equivalent but now are not.

I actually need some help here. What does genetic variation mean? Seems to mean the number of point mutations in a gene, compared to an a priori?

 

[Skrambles]

Genetic variation is a statistical measure of the differences between genomes in a population. It is not limited to point mutations, but those would definitely contribute to variation.

http://en.wikipedia.org/wiki/Genetic_variation

http://en.wikipedia.org/wiki/Founder_effect

 

[bobze]

I found this link - http://www.physorg.com/news183278038.html

I have heard the stuff before about the Alu markers. It's amazing what they can do with 2 samples.

The article starts out - "Modern humans are known to have less genetic variation than other living primates"

Someone in the comments made an interesting observation - "I wonder why these disasters endangered humans, lowering our genetic diversity, but didn't do the same to most other animals.." (especially other primates??)

I have no answer.

Other mammals of the region, in deed even other primates also experienced a bottleneck around that time. See; Martin[/PLAIN] Williams, Did the 73 ka Toba super-eruption have an enduring effect? Insights from genetics, prehistoric archaeology, pollen analysis, stable isotope geochemistry, geomorphology, ice cores, and climate models, Quaternary International, Available online 9 April 2011, ISSN 1040-6182, 10.1016/j.quaint.2011.03.045.
(http://www.sciencedirect.com/science/article/pii/S1040618211001911)

Humans have been experiencing low population numbers for a long time, geologically speaking. Think of it as "extended bottlenecking", which would account for why our variation is lower than other primates.

Also an important point to remember is that we are talking about ancestors. That isn't to say that Toba would have wiped out all humans on Earth at the time except for a small group--Only that one of the pockets of humans that survived the eruption (those estimated 10,000 individuals) were the only ones that went on to become ancestors of all modern humans.

It seems likely that that is probably a recurrent trend in human evolution where we have small isolated pockets, that later become ancestral.