Saturday, June 9, 2012

A New Cause for the Genetic Bottleneck?

Most of you are probably aware of the theory that at sometime between 50,000 and 100,000 years ago, the human population was reduced to between 1,000 and 10,000 mating pairs, creating a genetic "bottleneck." The most widely theorized cause for the bottleneck was the eruption of a super volcano located at Lake Toba (Sumatra, Indonesia) approximately 73,000 years ago. It is believed that the eruption caused a 6-7 year volcanic winter, and ushered in a 1,000 year cooling period. (See also here).

(We know this is bunk because all global climate variation is caused by humans producing CO2 through their nasty SUVs and general enjoyment of a higher standard of living).

The Daily Mail reported earlier this week about another possible explanation:
The key factor which separated man from our evolutionary rivals 100,000 years ago may not have been language - but instead a mysterious plague.

The plague ravaged populations of early humans in Africa, until just 5-10,000 were left.

But from that small population, humans emerged - and triumphed over other evolutionary cousins such as Neanderthals.

The bug attacked small infants and newborns, causing symptoms similar to sepsis or meningitis.

But suriving it seems to have conveyed a key advantage.

Soon afterwards, homo sapiens expanded dramatically in numbers, and spread all over the Earth.

Researchers found that human populations today have 'dropped' two genes which related primates - apes - have, which could have left early man vulnerable to infections.

The infections are related to modern bugs such as E Coli.

‘The modern bugs can still bind and could potentially have altered immune reactions,’ said Ajit Varki, MD, professor of medicine at UC San Diego

'Though it is impossible to discern exactly what happened during evolution, the investigators studied molecular signatures surrounding these genes to hypothesize that predecessors of modern humans grappled with a massive pathogenic menace between 100,000 and 200,000 years ago.

'This presumed ‘selective sweep’ would have devastated their numbers. Only individuals with certain gene mutations survived – the tiny, emergent population of anatomically modern humans that would result in everyone alive today possessing a non-functional Siglec-17 gene and a missing Siglec-13 gene.'

It's widely known that 100,000 years ago, human evolution reached a mysterious bottleneck.

The cause of the bottleneck remains unsolved, with proposed answers ranging from gene mutations to cultural developments like language to climate-altering events, among them a massive volcanic eruption.

‘In a small, restricted population, a single mutation can have a big effect,’ said senior author.

‘We've found two genes that are non-functional in humans, but not in related primates, which could have been targets for bacterial pathogens particularly lethal to newborns and infants.

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