The Evolution of
Senescence and Death
Agreat many discussions about the evolution of senescence begin with the question of how senescence could have evolved in the first place. This question has long puzzled some of the best thinkers in evolutionary biology and genetics. Senescence as we understand it in eukaryotes does not exist, or at least has never been reliably detected, in prokaryotic organisms. It seems to have evolved very early in eukaryotic history, close in time to their emergence from the prokaryotes and to the beginning of the use of sex in reproduction.
From our understanding of the principles of evolution and natural selection, it is easy to imagine how traits like increased physical vigor, better eyesight, or brighter plumage for attracting mates—traits that would increase reproductive fitness or prolong the reproductive lifespan of an individual organism—could arise within, and eventually come to dominate, a breeding population. It is less obvious how something like senescence—which severely impairs an organism's ability to function in its natural environment—could have been positively