Unformatted text preview: Bio 1B, Summer 2009 Evolution, Lecture 5 Professor Alan Shabel Page 1 of 1 Updated on 29 June 2009 EVOLUTION, LECTURE 5: NATURAL SELECTION AND ADAPTATION (487–498, 523–525) The normal distribution in statistics describes a data set that clusters around a mean in a bell- shaped curve ( bell curve ), and many quantitative organismal traits are distributed normally within a population. Natural selection alters the distribution of heritable traits in a population in three main ways, depending on which phenotypes are favored: directional selection , stabilizing selection , and disruptive selection (see Figure 23.13). I gave examples of each of these modes of selection in lecture: an example of directional selection is the high mortality of small-bodied swallows after a frigid winter; an example of stabilizing selection is the higher mortality suffered by human newborns at the extreme ends of the body mass spectrum; and an example of disruptive selection is the relatively lower fitness of...
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This note was uploaded on 07/04/2009 for the course BIO 1B taught by Professor Carlson,mischel,power during the Summer '07 term at Berkeley.
- Summer '07