A big hand for the little guys

摘要

The secret to what makes us human may lie not in our brains, but in sperm. Tiny changes in these little cells may have made all the difference to our evolution. DNA is packed into sperm heads by proteins called protamines, which help to squash the chromosomes into a tiny space. These proteins were never considered very important in human development because people thought their influence stopped shortly after fertilisation. But Caro-Beth Stewart at the University of Albany, State University of New York says these proteins evolved with lightening speed just as humans split from the common ancestor of animals like gorillas and chimps, indicating that the proteins have a much bigger role in human development than previously thought. Researchers are constantly on the hunt for ways of explaining why humans are so different, and so much brighter, than our close relatives (New Scientist, 23 February, p 15). Chimpanzees and humans parted ways only 5 million years ago, leaving us with 98.5 per cent of the same DNA. Working out how the remaining 1.5 per cent of our genetic make-up can explain all the differences between species is proving tough.