Bio 575 chapter 04 09

Bio 575 chapter 04 09 - Chapter 4 Robert Arking Biology of...

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Unformatted text preview: Chapter 4 Robert Arking Biology of Aging, 3e Oxford University Press Wayne State University Outline r-selected If carrying capacity of environment changes, then population density will change accordingly. Example: Homo sapiens Long-lived animals take longer to reproduce than short-lived animals Long-lived animals have fewer offspring than Short-lived animals If the name of the game is to get more copies of your genes into the next generation, then what is the value in having fewer offspring? Basic Concepts Underlying the Evolutionary Theory of Aging 1. Natural environment is hazardous. 2. Populations are genetically diverse 3. Therefore, differential survival of different genotypes occurs (e.g. evolution by natural selection takes place) 4. All populations are also age-structured 5. Therefore effect of natural selection is highest at beginning of reproductive phase and lowest at the end of reproduction 6. Therefore deleterious mutations that act late in life will not be subject to stringent natural selection so as to eliminate them. But there will be sufficient selective pressure to delay the onset of their effects until late in life, near the end of reproduction, after which loss of function will become noticible. 7. Alternative outcome is that some genes may have beneficial effects early in life but deleterious effects later in life. Such pleiotropic genes would be selected for on the basis of their early benefits, thus insuring loss of function in later life. 8. Wild populations will have very few older individuals. Aging is a characteristic only of populations living in situations where environmental hazards have been drastically decreased. Life History, Fecundity and Longevity Alternative Life History Strategies: Reproductive (r vs K): many vs. few Survival ( size as an example ): large vs. small…. ….larger is faster but takes longer to develop So which is better: lots of small slow offspring or a few big offspring? Outcome of the Choice: Larger animals generally have a longer mean and maximum life span than do smaller animals – But note that there is no direct selection for longevity*....
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This note was uploaded on 08/05/2010 for the course BIO 5750 taught by Professor Arking during the Winter '09 term at Wayne State University.

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Bio 575 chapter 04 09 - Chapter 4 Robert Arking Biology of...

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