A bird that risks her life to lead a fox away from her chicks may be influenced by a "selfish gene" (Dawkins, 1976). Genes can't think, of course. However, a gene causing behavior that risks the loss of one copy of itself (in the mother) will become more common over time, if this same behavior often saves more than one copy of itself (in the chicks). The gene can be considered "selfish", in the sense that the welfare of the mother, her species, or the whole ecosystem only indirectly affect the gene's spread. It's as if each gene were at war with rivals (other versions of the gene, or alleles) for its place on the chromosome.
The selfish gene concept is now being used to design new methods to control the spread of disease. Mosquitoes that resist infection by the malaria parasite can be made by genetic engineering. Unfortunately, the small benefit (to a mosquito) of resistance to this parasite is probably not enough for resistant mosquitoes to take over in the wild, because most of the animals they bite aren't infected. (It would be nice if the laws of nature always favored human welfare, but they don't.)
How can we make such beneficial genes spread through mosquito populations? This week's paper, "A Synthetic Maternal-Effect Selfish Genetic Element Drives Population Replacement in Drosophila" by Chun-Hong Chen and colleagues at Cal Tech and UCLA, published on-line in Science, demonstrates one interesting approach.
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