A new genetic study suggests that humans reached America no earlier than 18,000 years ago. The authors base their conclusion on research into mutations on the form of the human Y chromosome known as haplotype 10. The scientific community has been divided on this subject. Some researchers believe that America was first populated 13,000 years ago, at the end of the last Ice Age. Others propose a much earlier date – around 30,000 to 40,000 years ago, at the same time that people were moving into Europe.
     Haplotype 10 is one of only two haplotypes carried by Native American men and is thought to have reached the continent with the earliest migrations. This haplotype is also found in Asia and confirms that the colonists originated there. If it could be determined when mutations on haplotype 10 occurred, it might give a date for the first populations in America.
     Native Americans carry a mutation called M242 which is found in both Asia and America. The first Americans were, therefore, still living in Asia when the mutation occurred. Calculations based on the rate at which DNA on the Y chromosome mutates, combined with the time taken for a single male generation, gave a maximum date of 18,000 years ago for the first appearance of M242. Migration eastwards into America could only have taken place after this date. Dr. Spencer Wells, geneticist and contributing author, said: “I would say that they entered within the last 15,000 years.”
     In 1997 a US-Chilean team claimed that burnt wood and fractured pebbles found in 33,000-year-old sediments in Chile were evidence of hunting camps. The interpretation of these remains has, however, been questioned by experts. Dr. Wells has acknowledged the possibility that older American populations carrying unidentified haplotypes could have been swamped by the later migrations, with the result that the genetic record was erased. “We can’t rule that out, but in science we have to deal with what’s extant.” The research is to be published in the American Journal of Human Genetics.

Source: BBC News (22 July 2003)