What exactly is genetic bottleneck the scientists refer to?

[strategist.com]

After the Toba supereruption, there is genetic bottleneck which means little genetic variation among the surviving species. What exactly do the scientists mean by 'little genetic variation?'

[Manco]

Very basic explanation:
When there's few people left, that also means there are few distinct full sets of genes around.
Since children's genetic code is pretty much 50/50 of each respective parent with only a few mutations, that means that all coming generations only have the genepool of those few people who survived the Eruption, though mixed and matched due to all the interbreeding, + whatever mutations have managed to crop up.

To once again have large genetic variation, you'll need a huge timespawn so that each success generation can add more and more mutations leading to more variety.

[John I Tzimisces]

I'm going to out-simple-explanation Manco (unless you don't like basic math)

Say you've got 100 people in a population, half of them are brunette, half are blonde. A landslide happens and kills all the brunettes. 100% of the population is now blonde. Genetic bottleneck. If the landslides kills half the brunettes, the population is now 75% blonde. Also a genetic bottleneck.

They can be species-wide, or restricted to a particular area/population, depending on the circumstances.

[Nikitn]

If the landslides kills half the brunettes, the population is now 75% blonde. Also a genetic bottleneck.

75% of the population survived, and now 50/100*0.75 = 2/3 = 66% of the population is blonde. Not 75%, unless I did something wrong.

But regardless, wouldn't the remaining brunettes be enough to restore the brunette gene in the general population?

[Phier]

But regardless, wouldn't the remaining brunettes be enough to restore the brunette gene in the general population?

A bit too complext for 830 am but...

http://en.wikipedia.org/wiki/Fixatio...on_genetics%29

[John I Tzimisces]

75% of the population survived, and now 50/100*0.75 = 2/3 = 66% of the population is blonde. Not 75%, unless I did something wrong.

But regardless, wouldn't the remaining brunettes be enough to restore the brunette gene in the general population?

oh no your math is correct, I was typing too fast. derp.

anyhow, if the landslide was the only operating force (which it pretty much would never be) on the presence of blondes and brunettes, then the population's blonde to brunette ratio would remain static. If brunettes had slightly higher reproductive success, then over time, they would ultimately become the sole hair color or allele or whatever.

[Phier]

oh no your math is correct, I was typing too fast. derp.

anyhow, if the landslide was the only operating force (which it pretty much would never be) on the presence of blondes and brunettes, then the population's blonde to brunette ratio would remain static. If brunettes had slightly higher reproductive success, then over time, they would ultimately become the sole hair color or allele or whatever.

The part it was too early to get into would be the idea of neutral drift. Even if there were no selection pressure for blonde or brunette, over time one could be come the only allele. Then there is also the concept of the "rare male" which I think applies to females as well. If there were few brunettes they may have a selection advantage but if they were to become dominant than that advantage would switch to blondes.

[hellheaven1987]

anyhow, if the landslide was the only operating force (which it pretty much would never be) on the presence of blondes and brunettes, then the population's blonde to brunette ratio would remain static. If brunettes had slightly higher reproductive success, then over time, they would ultimately become the sole hair color or allele or whatever.

Probably not, consider brunette probably is a heterozygous trait, which means after few generations brunette would still become dominate again.

[strategist.com]

Thanks for the answer lol. I have another question, what was the significance of the Toba supereruption in the human evolution? As far as I know it did accelerate human evolution but what was the significance in genetic level?

[hellheaven1987]

Thanks for the answer lol. I have another question, what was the significance of the Toba supereruption in the human evolution? As far as I know it did accelerate human evolution but what was the significance in genetic level?

The idea is that Toba event caused a sharp reduce of ancient human population and hence resulted a genetic bottleneck since few individuals lived after the event. In the same time, however, the surviving population was "natural selected" by the event hence they could live the post-catastrophic period better, resulted a rapid expansion of human species into the new space (remember that, Toba event caused not just the population reduction of human but whole Earthlings, hence many dominated species in some regions would die off too and allowed ancient human to explore the gap).

[Phier]

My point was simply that the Chinese ridiculous cultural affection for women with small feet that lead to feet binding is not dissimilar to other "natural" sexual selection pressures like having idiotically long tails. There is endless debate on this as to "why" in evolutionary biology discussions.

[Nikitn]

Perhaps long ago it was a useful feature to sexually-select mates with longer tails, but by now it has run out of control? I mean no way could it ever be useful to have tail-length of that magnitude.

[Nimthill]

Good example are big boobs: we all like them, but why? Having an extra layer underneath her mammary glands doesn't give a female any advantage except for the fact that it allows her to attract males better.

One of my profs (Biology and Pathology) claimed that 30.000y ago women didn't have breasts as we know them today. Good job guys!