According to a recent study done by scientists from the Arctic Monitoring and Assessment Programme (Amap), man-made chemicals found in high concentrations in the blood of pregnant women in some Arctic villages appear to be causing drastic changes in the traditional gender ratios of their offspring.
Recently, the historical sex balance of the human race has begun to change around the world as well. Throughout history there has usually been a slightly greater number of males than females born each year, but a paper published in the US National Institute of Environmental Health Sciences this year said that in Japan and the US there were 250,000 boys fewer than would have been expected had the sex ratio existing in 1970 remained as it was.
http://www.treehugger.com/files/2007/09/manmade_chemica.phpcould be something for india and china who have to few girls wouldn't it?