I'm fascinated by the implications of a new study of Native American DNA:

If future research comes to the same conclusions, we have yet another clue into just how amazing the conquest of this planet by modern humans really was.

Anatomically and behaviorally modern humans had emerged in Africa 100,000 years ago, give or take. But it wasn't until about 50,000 years ago, when the population of homo sapiens in East Africa may have been as low as a few thousand, that one or two small groups left. Scientists are pretty sure that one group, possibly as small as 150 people, crossed the Red Sea into what's now Yemen. A second group may have left Africa farther north, entering the Middle East through the Sinai.

Whether they started off as one or two groups, they soon split off, with one moving north and west to populate Europe, and the other moving east into Asia, including New Guinea. One branch of the European group also went into Asia, ending up in Australia.

And, as the new research suggests, a small and admirably plucky group of humans managed to emigrate from Beringia, the now-submerged land bridge between Siberia and Alaska, into North America. Their descendants didn't just survive, they populated two continents, eventually hunting dozens of species of megafauna into extinction. By the time the first Europeans arrived with their deadly diseases, the Native American population may have surpassed 100 million people -- more than lived in Europe in 1491. By the mid-1600s, as many as 95 percent of them may have died from diseases against which their non-diversified immune systems were helpless.

Mammoths they could handle. Smallpox, not so much.

Weekend blog meat

• Still more confirmation that a little exercise goes a long way.
• Why the obese are more likely to survive a critical illness. (Hat tip: David MacRury.)
• Sucralose is the sweetener that just keeps on sweetening. (Hat tip: Anthony McInnis.)
• Finally, here's an interesting addition to yesterday's post: Sudhir Venkatesh explains the economics of high-end prostitution. His thesis: If Eliot Spitzer had been willing to pay more for his hookers, he wouldn't have gotten caught.