GENETIC-VARIATION AND AGING

Life span is subject to genetic modification in yeasts, nematodes, fru it flies, mice, humans, and other vertebrates and invertebrates. There are a few single-gene mutants known that extend life span in yeast an d nematodes; in other experimental systems the chat-deter is treated q uantitatively, and generally has a low to moderate heritability. Life span responds to artificial selection in Drosophila and Caenorhabditis . There are many candidate genes presently under investigation, includ ing the anti-oxidizing enzymes and heat-shock proteins. The main evolu tionary models of senescence are antagonistic pleiotropy and mutation accumulation, neither of which has substantial experimental support. T he incorporation of analytical techniques from demography is playing a n increasing role in research on aging.