Our Genes May Prove It: We Are Family
Humans are all so closely related that our entire population shows less genetic diversity than that of a small group of chimpanzees. It’s almost as though we all came from the same town—and perhaps we did. This year geneticists announced that each of us is descended from a population made up of as few as 2,000 hunter-gatherers who lived in northern Africa between 70,000 and 140,000 years ago. If the analysis holds up, it supports the controversial out-of-Africa theory that Homo sapiens evolved in Africa before migrating to other continents.
This scenario is based on a study by Marcus Feldman, a population geneticist at Stanford University; Noah Rosenberg, a computational biologist at the University of Southern California in Los Angeles; and Lev Zhivotovsky, a geneticist at the Russian Academy of Sciences in Moscow. They examined short, repetitive fragments of DNA called microsatellites, markers found in every person. “We used 377 markers that are generally located in noncoding regions of the genome, ones that are likely to be neutral, where there is no natural selection involved,” says Rosenberg. The beauty of microsatellites is that they mutate frequently and at a steady pace, enabling scientists to infer from them when human populations first diverged from each other. Studying those mutations in 1,056 individuals clustered in 52 population groups around the world allowed researchers to plot successive waves of migration to Europe, Asia, and the Americas after those first hunter-gatherers left Africa. “We’re now trying to confirm these results using different models of how evolution took place,” says Rosenberg.
—Michael W. Robbins
This Very Old American House Sheltered Prehistoric Nomads
The place doesn’t look like much, just a circular pile of slab-shaped rocks weighing about 50 pounds each. There are also subtle signs of fire damage: bits of mud used as mortar have a burnished red hue, like clay baked in an oven. All things considered, however, the recently unearthed site is remarkably well preserved. Dozens of stone knives, scrapers, and spear points found there suggest it may have been a weapons-making depot for Folsom hunters, prehistoric nomads who roamed North America more than 10,000 years ago.
The most extraordinary thing about the crude shelter is its location, on top of Tenderfoot Mountain, an 8,600-foot mesa in the southern Rockies near Gunnison, Colorado. Folsom hunters ambushed and speared bison and elk on the Great Plains, from what is now Nevada to Iowa, and researchers had surmised that they must have lived in ephemeral hide shelters that left no traces. “It could be that we’ve had blinders on and that the Folsom people were more mountain oriented than we thought,” says Mark Stiger, an anthropologist at Western State College in Gunnison. “Perhaps they just hunted on the plains but lived up here the rest of the time.”
Stiger began digging on Tenderfoot after he happened upon some bits of Folsom spear points while surveying the proposed site of a communications tower. He has since identified 15 other Folsom-era sites on the mountain that have yet to be unearthed. “There wasn’t any surface evidence of the house on the area we excavated,” Stiger says. “The other areas may have houses, or they may be something different. We’ll see.”
—Michael W. Robbins
Land Bridge Theory Tested
The most plausible explanation of how humans first settled the Americas—Ice Age hunters pursuing game walked from Siberia to Alaska over a land bridge—has gained wide acceptance in recent years, although scientific evidence has been thin at best. In 2003, it got thinner.
The yardstick for determining when the hunters crossed over is farther south, in Clovis, New Mexico. There the oldest archaeological site in North America with reliably dated tools and artifacts shows a human presence as early as 11,500 years ago. For the land bridge concept to hold, sites much older than Clovis would have to be found along the route. Only one has been found—at Ushki Lake, along the Kamchatka River, in Siberia. It was discovered in 1964 by archaeologist Nikolai Dikov, who found spear points and tools that he carbon-dated to about 14,300 years old. That would have given tribes sufficient time—3,200 years—to trek over the land bridge and down to Clovis.