Sperm wars

Scientists have found that the genes involved in the production of sperm have been evolving at a much faster rate than most other human genes. This insight into the evolution of human procreation has been extracted from the DNA data of the federal human genome project.

The scientists, from the University of Chicago, have looked at three genes involved in sperm production. Two of the genes make protamines, special DNA packing materials, that govern the shape and size of the sperm. They found that human protamines have evolved very rapidly. In studying the complementary genes in other primate species, the research team has concluded that the protamine genes of chimpanzees have evolved as fast, but that in gorillas, the development of the genes was much more slow. It is believed that this is linked to the mating patterns of the species. Gorillas operate a 'harem' system whereby one male controls access to many females. Presumably because males can thus be more sure of their paternity, their sperm has not had to compete so strongly. Thus the genes that control the sperm development in the gorilla have evolved more slowly than in the chimpanzee. A female is likely to mate several times, so the males need more 'competitive sperm' to secure paternity.

The finding implies that in the human evolutionary past, women generally had many sexual partners, therefore, the sperm of the males need to compete with one another in order for the male to achieve fatherhood. Professor Chung-I Wu has said the research, published in Nature, says more about the competition between men than the 'battle of the sexes'. He said 'the simplest explanation is that sperm compete for eggs, but eggs don't compete for sperm' and that because of this it is presumed that 'genes governing male reproduction are under pressure to evolve'.