Darwin Snails Discussion

As previously stated the original hypothesis constructed before the experiment was, if there is predation by crabs present and the trait of shell thickness is being observed, then evolution by natural selection will occur and a shift to a larger average shell thickness in the experimental tanks containing the Dogwinkle snails can be expected. Based on the results it is fair to conclude that this hypothesis is supported and that when predation by crabs is present evolution by natural selection occurs. This can be concluded because in all trials the average shell thickness of the tanks with crabs, the experimental population, increased significantly from day zero to day 160. For example in Figure 1 the average shell thickness of tanks with crabs increased from 7.175mm on day 0 to 8.875mm on day 160, a total increase of 1.7mm. Meanwhile there was no trend within the tank without crabs, the control population, and the change of average shell thickness within the population was either random or insignificant. For example in Figure 1 the average shell thickness of the tanks without crabs in them change from 7.175mm to 7.4mm, a total increase of .225mm, a much less significant change than the 1.7mm observed in the tanks with crabs. This change in the experimental population proves that evolution by natural selection occurred when predation by crabs was present because the fact that the trait of shell thickness was heritable and variable was already known, but the significant change from thinner to thicker shells in populations where predation was present proves that there is a selection differential when discussing shell thickness, more specifically it can be concluded that thicker shells provide the organism a higher probability to survive and reproduce. This conclusion reiterates the three requirements needed for evolution by natural selection to occur being, heritability, variability and selection differential. Also the interval and duration of the experiment being only 160 days shows exactly how quickly and effectively natural selection can occur in and change a population.