I was intrigued to read an article about the human genome at The Daily Galaxy. Here's an excerpt.
"Each little piece of the genome has its own unique bit of history and goes to a unique ancestor as you go further and further back," explained John Novembre, a population geneticist at UCLA. "As you look at different parts of the genome, you get access to different parts of history."
On the basis of this principle, Richard Durbin, a genome scientist at the Wellcome Trust Sanger Institute near Cambridge, UK, and Heng Li determined a way to calculate, from the ages of different segments of a single person's genome, changes in the population size of their ancestors.
The genomes of Venter and two others of European ancestry, two Asian men and two West African men all tell the same story up until about 100,000 years ago, when their populations began to split and then plummet in size, reflecting, it is believed, the first human migrations out of Africa.
The ancestors of Asians and Europeans dwindled by a factor of ten to roughly 1,200 reproductively active people between 20,000 and 40,000 years ago, Durbin and Li calculated. African populations also crashed, but by nowhere near the same extent, dropping to around 5,700 breeding individuals. Other studies have recorded population crashes at around the same time, Reich says.
. . .
Mining individual genomes can't reveal every chapter of human history, notes David Reich, who works with Li at the Broad Institute of Harvard and MIT in Cambridge, Massachusetts. The approach reveals little about upheavals of the last 20,000 years, such as the peopling of the Americas, because few chunks of the genome are young enough. Similarly, Durbin and Li's method can't deduce the history of human ancestors who existed before about 2 million years ago because few regions of the genome are much older.
There's more at the link. Highly recommended reading.
It's actually pretty scary to think how humanity dwindled to no more than a few thousand individuals, a few tens of thousands of years ago. A tiny population like that would have been terrifyingly vulnerable to the whims of nature. If things had gone badly for them, there wouldn't be a human race today, and this planet would be populated only by plants and animals. I wonder what happened to reduce humanity's numbers to such a tiny margin? And how did those few humans manage to survive, and recover, and rebuild their numbers?
Call it Divine intervention, if you will, or sheer blind luck, or whatever: but I guess we'll never know for sure . . .