BIOC51H3 Lecture : Readings 3 notes
11 Aug 2010
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Readings 3
-a trait, or integrated suite of traits, that increases the fitness of its possessor is called an
adaptation, and is said to be adaptive
-in order to demonstrate that a trait is an adaptation, first determine what a trait is for and
then show that individuals possessing the trait contribute more genes to future generations
than individuals lacking it
-through experimentation, Weeks was able to conclude that oxpeckers have no discernable
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-Weeks also concluded that oxpeckers spend a considerable fraction of their feeding time
drinking blood from open wounds and cleaning earwax from their hosts
-the oxpecker experiments demonstrate that we cannot uncritically accept a hypothesis about
the adaptive significance of a behaviour simply because it is plausible
-differences among populations or species are not always adaptive (oxpeckers with different
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-not every trait of an organism, or every use of a trait by an organism, is an adaptation (the
feeding habits of an oxpecker may or may not create mating opportunities)
-not every adaptation is perfect (feeding on blood and earwax may not be sufficient because
its an unpredictable food supply)
-a well designed experiment allows scientists to isolate and test the effect that a single, well
defined factor has on the phenomenon
-the first step in any evolutionary analysis is to phrase the question as precisely as possible
because it makes it easier to design an experiment that will provide a clear answer
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many competing hypotheses as possible
-defining and testing effective control groups is critical in order to compare
-all treatments must be handled exactly alike in order to avoid bias and increase precision of
the data
-randomization is a key technique for equalizing other miscellaneous effects among control and
experimental groups and another way to avoid bias
-repeating the test on many individuals is essential (larger samples are better in estimating a
quantity)
-replicated experiments reduce the amount of distortion in the estimate caused by unusual
individuals or circumstances
-replicated experiments allow researchers to understand how precise their estimate is by
measuring the amount of variation in the data
-knowing how precise the data are allows the use of statistical tests
-in a statistical test, the first step is specifying a null hypothesis which states that there is no
difference between the groups
-the second step is to calculate a value called the t-statistic that characterizes the magnitude of
the difference between the groups
-the third step is to determine the probability that chance alone could have made the test
statistic as large as it is
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