SSS 2010-01-21

（单词翻译）

At one time or another, you’ve probably said, “It’s a small world.” Well, it used to be much, much smaller. Because according to scientists from the University of Utah, about a million years ago our ancestors numbered fewer than 20,000. The estimate appears in the Proceedings¹ of the National Academy of Sciences.

The scientists based this ancestral census² on a reading of modern human genomes. In particular, they tracked the positions of transposable elements. These small pieces of DNA³ are basically genomic parasites⁴. Over time, they’ve spread through our genomes and though they’re still capable of hopping⁵ from one place to another, they do so quite rarely. One particular transposon first appeared about a million years ago. And by seeing where these sequences now sit, scientists can get a sense of the size of the breeding population back then.

Their estimate of 18,500 individuals is pretty sparse⁶ considering that these early humans were spread across the Old World. By comparison, some 25,000 gorillas⁷ and 21,000 chimps⁸ were concentrated in Africa alone. So a million years ago, we were essentially⁹ an endangered species. Here’s hoping our recovery is permanent.