Relatively Higher Speed of Individual Pill Bugs Allow for Higher Chance of
Being Biologically Fit
William Seo
Abstract
Among many traits, the speed of individual pill bugs was noticed to vary greatly in the
population. Since this trait varied, it was assumed that selection would act on it and the group
hypothesized that if a pill bug is relatively faster than other individuals, than it will have a greater
chance of survival, increasing the average speed of a pill bug population from the original to the
evolved population. In order to test this hypothesis, the average time for a pill bug to travel six
inches was calculated using a sample of five pill bugs. Following this, the time it took an
individual pill bug to travel six inches was recorded and was compared to the average speed—if
it was faster, then that individual survived predation and if it was slower, then that individual
died by predation. At the conclusion of the experiment, it became obvious that selection would
favor higher speeds in pill bugs because only six of the possible 20 pill bugs survived predation,
resulting in a directional mode of natural selection.
Methods
In this experiment, the speed of each pill bug was observed. First, in order to establish a
baseline for the average speed of a pill bug, the average time it took one pill bug to travel six
inches, which was found to be 0.645 in./second, was calculated using a sample of five random
pill bugs. Because the data being collected (speed) has multiple variables that affect it, a sample
of 20 pill bugs was used to minimize errors. These 20 pill bugs were timed to see how long it
took each individual pill bug to travel six inches and if the pill bug traveled the six inches in less
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time, then that pill bug survived predation while if a pill bug traveled the six inches in more time
than the average, then that pill bug died due to predation. The data was tabulated to determine
which pill bugs survived and which pill bugs did not survive. Finally, to check if the data yielded
significant data (data not due to chance), a onetailed ttest was used, relating the significance of
average speed of dead individuals to that of surviving individuals, to determine the pvalue. If
the pvalue calculated was less than 0.05, then the null hypothesis that the average speed of pill
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 Spring '08
 Staff
 Null hypothesis, Statistical hypothesis testing

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