Humans Barely Dodged Extinction----

[indigobusiness]

Humans

DNA evidence suggests that humans today are a legacy of a population bottleneck which occurred 70,000 years ago. This would have had the result of limiting the overall level of genetic diversity in the human species, possibly by a large amount. One theory about this bottleneck is the Toba catastrophe theory, positing that the human population was reduced to a few thousand individuals when the Toba supervolcano in Indonesia erupted and triggered a massive environmental change.

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



Population Bottlenecks and Volcanic Winter

The "Weak Garden of Eden" model for the origin and dispersal of modern humans posits a spread around 100,000 years ago followed by population bottlenecks. Then, around 50,000 years ago, a dramatic growth occurred in genetically isolated, small populations. In a 1998 article, Stanley Ambrose proposed an alternative hypothesis, a volcanic winter scenario, to explain recent human differenciation. The bottleneck was caused by a volcanic winter resulting from the super-eruption of Toba in Sumatra. If Ambrose's hypothesis is correct, modern human variations differentiated abruptly through founder effect, genetic drift, and adaptation to local environments after around 70,000 years ago.

Ambrose points out that the Out of Africa dispersal date of around 100,000 years ago fits the generally warm, humid last interglacial period, 130 -74,000 years ago. An impressive body of paleontological evidence shows an Afro-Arabian biotic community expanded northward during this period. Several such multi-species dispersals out of Africa have occurred during previous interglacial phases. He considers the variants of the Replacement model to be more accurate and realistic than the Multiregional models.

The number of DNA mutations within a population increases temporally. When a population has passed through a bottleneck, the mutation distribution evidences the bottleneck. DNA studies have identified a significant bottleneck (or bottlenecks) during the last glacial period.

The Multiple Dispersals model proposes a population bottleneck occurred when cold, dry climates isolated populations in Africa. Additional bottlenecks occurred through physical bottlenecks such as the Sinai Peninsula. The first dispersal of anatomically modern humans, to the Levant around 100,000 year ago, is evidenced by early modern human skeletons in the Near East. According to Ambrose, this first dispersal apparently failed to permanently establish modern humans outside of Africa. Genetic evidence shows that non-African populations can be divided into southern Australasian and northern Eurasian populations that divided 50-75,000 years ago.

snip

http://www.jqjacobs.net/anthro/paleo/bottleneck.html

Human Evolution

The New Batch - 150,000 Years



How did we escape extinction?

What makes us so special?

How we colonised the world.

With just over 6 billion people living in the world today, human beings are a phenomenally successful animal. But our species, Homo sapiens, once came close to outright extinction.

Social networks spread the risk of survival during the bottleneck
Clues from genetics, archaeology and geology suggest our ancestors were nearly wiped out by one or more environmental catastrophes in the Late Pleistocene period. At one point, the numbers of modern humans living in the world may have dwindled to as few as 10,000 people.

http://www.bbc.co.uk/science/cavemen/chronology/contentpage6.shtml