A human migration fueled by dung?

When people made their way from Asia to the Americas, the path they took may have been covered in dung.

At the peak of the last ice age, when sea levels were low, a land bridge that's now submerged in many places connected what are now Alaska and northeastern Russia. Although much of the area was dry more than 50,000 years ago, firm archaeological evidence of human occupation in this region dates to only around 14,000 years ago, says David Rhode of the Desert Research Institute in Reno, Nev. Recent genetic data supports this timing (see story p.84). Some scientists have proposed that humans took so long to migrate into this frigid, treeless expanse because there wasn't any wood for heating or cooking.

Rhode and his colleagues, however, contend, people could have burned dried dung.

Today, many residents of the Tibetan Plateau use yak dung for almost all of their heating and cooking needs. A single family living in a 10-square-meter tent requires between 25 and 40 kilograms of dried dung per day in the summer and about twice that in the winter, says Rhode. That adds up to about 20 metric tons of dung per year. Although that sounds like a huge amount, Rhode and his team observed one group of Tibetans collect about a quarter-ton of dung from their yak herd's pasture in just 4 hours. The researchers estimate that one person could gather an entire family's average fuel supply in less than 1 hour per day.

Today's conditions on the Tibetan Plateau match the cold, arid climate of the ancient land bridge's tundra. Scientist believe that the region then supported large populations of herbivores such as bison, mammoths, horses, and wooly rhinoceroses (SN: 4/19/03,p.244). Unless there were far fewer of these animals than currently estimated, there should have been plenty of dung available for fuel, says Rhode.--S.P.