BIOL 336 Lecture Notes - Lecture 15: Senescence, Mutation, Pleiotropy
Life History
Evolution
Lifespan not a simple function of heartbeats, metabolism, and body wearing out
Senescence
Deterioration with age
Extrinsic mortality (“bad luck”) – Causes of death for which genes can’t control (Accidents,
overwhelming predators, diseases, weather)
▪ Selection can’t help in this situation
Intrinsic mortality (“your own genes fault” – causes of death from developmental or survival
issues that genes could have solved (Ex. Cancer, heart attacks)
Intrinsic mortality evolves to match extrinsic mortality
▪ If extrinsic mortality tended to kill your ancestors by the time you were age X, then
intrinsic mortality will have evolved to kill you at about age X also, even if protected
from extrinsic mortality
▪ (Ancestors died at certain age, so you die at that age)
Why do we have genes that make us senesce? (Why doesn’t selection promote longetivity?)
Two theories:
a) Mutation accumulation theory
▪ Younger age = Make more babies at a time
▪ Older age = Fewer babies since likely death of individuals means # babies at later age
low
▪ Late-acting mutations accumulate – They are not selected against, since individuals
rarely live that long, and therefore almost no loss of reproduction. Reduces intrinsic
longevity.
o From mutations in the germ-line (Carriers)
L15
Document Summary
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