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Natural Selection Types of Natural Selection Natural selection can take many forms. To make talking about this easier, we will consider the distribution of traits across a population in graphical form. In we see the normal bell curve of trait distribution. For example, if we were talking about height as a trait, we would see that without any selection pressure on this trait, the heights of individuals in a population would vary, with most individuals being of an average height and fewer being extremely short or extremely tall. However, when selection pressures act on a trait, this distribution can be altered. Figure%: The standard distribution of a trait across a population Stabilizing selection <script language="JavaScript" type="text/javascript"> document.write('<a href="http://clk.atdmt.com/APM/go/sprkndrv0010000507apm/direct;wi.300;hi.250/01/" target="_blank"><img src="http://view.atdmt.com/APM/view/sprkndrv0010000507apm/direct;wi.300;hi.250/01/"/></a
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Unformatted text preview: >'); </script> <noscript><a href="http://clk.atdmt.com/APM/go/sprkndrv0010000507apm/direct;wi.300;hi.250/01/" target="_blank"><img border="0" src="http://view.atdmt.com/APM/view/sprkndrv0010000507apm/direct;wi.300;hi.250/01/" /></a></noscript> When selective pressures select against the two extremes of a trait, the population experiences stabilizing selection. For example, plant height might be acted on by stabilizing selection. A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The number of plants of medium height will increase while the numbers of short and tall plants will decrease. Figure%: The effect of stabilizing selection on trait distribution...
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