Natural selection.odt

35 views1 pages
Published on 19 Apr 2013
School
Simon Fraser University
Department
Biological Sciences
Course
BISC 110
Professor
Why does natural selection not result in perfect organisms?
Natural selection- the differential survival and reproduction of variant individuals within a
population- is the prime mechanism of evolutionary change. As individual organisms interact
with their environment, some individuals are more succesful than others in surviving,
obtaining energy, reproducing etc. These differences in individual reproductive success result
in changes in the genetic makeup of the population over time. These changes represent
evolutionary change and result in adaptation of organisms to their environment.
Tradeoff
Evolution by natural selection is, by necessity, a process of compromisse, in which costs are
minimized and benefits are maximized. The development of any structure, or the performance
of any behavior, carries with it a cost- in terms of time or energy- to an organism. If the
structure or behavior confers a significant benefit to the organism- a benefit that exceeds the
cost- then it will be favored by natural selection.
Physical Constraints
Natural selection also operates within a number of constraints imposed by the laws of
physics.
The basic laws of physics impose powerful constraints on the range of designs possible for
living organisms.
Historical Constraints
Each organism has an evolutionary history of descent with modification feom previous
ancestors. Complex structures, biochemical pathways, and behaviors are not designed from
scatch. Instead, existing structures, pathways and behaviors are co opted and modified by
new selective pressures, as organisms adopt new ways of life. Thus, an excellent design may
be unavailable to an organism because it represents too great a discontinuity from an existing
structue.
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Document Summary

Natural selection- the differential survival and reproduction of variant individuals within a population- is the prime mechanism of evolutionary change. As individual organisms interact with their environment, some individuals are more succesful than others in surviving, obtaining energy, reproducing etc. These differences in individual reproductive success result in changes in the genetic makeup of the population over time. These changes represent evolutionary change and result in adaptation of organisms to their environment. Evolution by natural selection is, by necessity, a process of compromisse, in which costs are minimized and benefits are maximized. The development of any structure, or the performance of any behavior, carries with it a cost- in terms of time or energy- to an organism. If the structure or behavior confers a significant benefit to the organism- a benefit that exceeds the cost- then it will be favored by natural selection. Natural selection also operates within a number of constraints imposed by the laws of physics.

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