Scientists have discovered yet another way we differ radically from our closest living relatives. This time up, menopause. Seems both chimp and human females lose their reproductive abilities at around age 40, but the chimp drop off is caused by, well, chimps dropping off. Those which manage to survive are actually more successful at raising the kids than the younger ones, and are preferred by male chimps perhaps because of this. The long post-reproductive survival period seems to be one of the most biologically distinguishing things about us.