The invention of agriculture has long been invoked to explain the spread of the Indo-European languages. Now, Dr. Jared Diamond of the University of California at Los Angeles and Dr. Peter Bellwood of the Australian National University in Canberra have applied the concept to 15 major language families. Their article appeared in the April 25 issue of Science.
The premise is that when humans lived as hunters and gatherers, their populations were small, because wild game and berries can support only so many people. But after an agriculture system was devised, populations expanded, displacing the hunter-gatherers around them and taking their language with them.
On this theory, whatever language happened to be spoken in a region where a crop plant was domesticated expanded along with the farmers who spoke it.
Even if the farmers interbred with the hunter-gatherers whose land they took over, genes can mix, but languages cannot. So the hunter-gatherers would in many cases have adopted the farmers language. That is why languages "record these processes of demographic expansion more clearly than the genes," Dr. Bellwood said.
Dr. Diamond said the new theory also predicted that expansions would occur more easily on an east-west axis than a north-south axis because the crop plants on which an agriculture depends tend to be able to grow only at particular latitudes.