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Over the past couple of thousand years, human beings have undergone evolutionary changes that caused their bodies to become smaller - and their brains to shrink, according to a new study published this week in the scientific periodical Proceedings of the National Academy of Sciences (PNAS).

The study, which was conducted by a group of researchers from the University of Wisconsin, suggests that, contrary to what scientists have believed until now, the pace of human evolution has in fact accelerated, and is now progressing at a faster rate than in the past.

The scientific narrative says that Homo sapiens first appeared on the planet 200,000 years ago in Africa. Their initial numbers are believed to have been in the thousands. Their habits were very different than modern man's, but biologically they belonged to our species.

Researchers traditionally believed that Homo sapiens has changed very little over the past few thousand years from a genetic point of view. But the new study says that humans are now evolving at a rate 100 times faster than during certain periods in the past.

"Ten thousand years ago, as men switched to an agricultural lifestyle, their bodies began getting smaller, and along with their bodies, their brains also decreased in size," anthropologist John Hawks told Haaretz. Hawks, who headed the team of researchers at Wisconsin, said nutritional changes constituted one of the reasons - but not the only one - behind the reduction in body size.

"Man himself has changed and become smaller," Hawks said. At the same time, the average height in the West began to grow during the past two hundred years. However, Hawks attributes that to better nutrition, rather than to genetic changes.