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Ryerson University
BLG 230

Chapter 13- Aging and Other Life History Characters • The branch of evolutionary biology that attempts to make sense of the diversity in reproductive strategies is called life history analysis • An organism truly perfected for reproduction would mature at birth, continuously produce high-quality offspring in large numbers, and live forever o This type of organism is called a Darwinian demon----no such organism exists • Trade-offs constrain the evolution of adaptations 13.1- Basic Issues in Life History Analysis • Fig 13.2 shows how a female opossum got her energy at different stages of her life, and the functions to which she allocated that finite energy supply • Female possum before she became sexually mature, the female used her energy for growth, metabolic functions like thermoregulation, and the repair of damaged tissues o After she became sexually mature, the female stopped growing, thereafter using her energy for metabolism, repair, and reproduction • Changes in life history are caused by changes in the allocation of energy o For example, a different female opossum might stop allocating energy to growth at an earlier age, thereby reaching sexual maturity more quickly  This strategy involves a trade-off: The female also matures at a smaller size, which means that she will produce smaller litters (babies) o Still another female might, after reaching sexual maturity, allocate less energy to reproduction and more to repair, thereby keeping her tissues in better condition  Again there is a trade-off: Allocating less energy to reproduction means having smaller litters (babies) 13.2- Why Do Organisms Age and Die? • Aging or Senescence- is a late-life decline in an individual’s fertility and probability of survivial • Documentation of a bird, a mammal, and an insect, all show declines in both fertility and survival • If everything else remains equal, aging reduces an individual’s fitness o Therefore aging should be opposed by natural selection • Two theories on why aging persists: o Rate-of-Living theory  Invokes an evolutionary constraint  Posits that populations lack the genetic variation to respond any further to selection against aging o Evolutionary theory  Invokes a trade-off between the allocation of energy to reproduction versus repair The Rate-of-Living Theory of Aging • Holds that aging is caused by the accumulation of irreparable damage to c
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