Experimental Report for EvolutionLab, Lab Report Example

Introduction

According to Charles Darwin’s theory of natural selection, traits are passed down over time if they allow a species to survive and reproduce. The alteration of traits that occur due to as a consequence of this phenomenon contribute to the evolution of a species, which allows them to change slowly over time. Ultimately, this results in extinction of some species who are unable to adapt or divergence of species that adapt to the environment differently.

In his experiments, Darwin postulated that the finches living in the Galapagos Islands currently have different beak sizes due to a divergent event that occurred during their evolutionary history. Since different food was available, some birds would eat small soft seeds and others would use hard seeds. Birds with small beaks were more efficient at eating small soft seeds and birds with large beaks were more efficient at eating large hard seeds. Therefore, these birds evolved in a manner that allowed more efficient food consumption in periods of food shortage.

Although Darwin stated that for a trait to evolve through natural selection, it must affect survivorship and reproduction, I hypothesize that it must also have variation among individuals for the trait the variation in the trait must be heritable.

Experimental Design

To determine how a trait must be heritable among individuals for a trait to evolve through natural selection, I kept beak size and variance constant for Darwin and Wallace Island, in addition to clutch size, island size, and precipitation. However, I changed heritability to 0.70 on Darwin Island and lowered it to 0.4 on Wallace Island. I recorded the results after leaving the population for 100 years.

To determine how a trait must have variation among individuals for a trait to evolve through natural selection, I kept beak size, clutch size, island size, and precipitation constant between the two islands, but changed variance to 2.0 for Darwin Island and 0.5 for Wallace Island. I recorded the results after leaving the population for 100 years.

Results

Figure 1 Heritability as a variable for natural selection

Figure 1 shows that the decrease heritability of beak size resulted in birds with smaller beaks on Wallace Island than on Darwin Island. This processes was slow, and the most noticeable different occurs in 2090, indicating that beak size continues to diverge over time. Ultimately, when a trait is inherited less, it is less likely to contribute to the population’s genetics.

Figure 2 Variability as a trait for natural selection

Figure 2 shows that there is a major difference between the beak size of the birds on Wallace Island and Darwin Island, beginning when the variability was selected. The birds on Darwin Island were given a wider range of beak size, so larger beaks were able to continue into the future, while the birds on Wallace Island were given a smaller beak size so this did not happen. It is unlikely that the birds on Wallace Island will recover a large beak size.

Discussions and Conclusions

These observations support the hypothesis that heritability and variability are necessary for the evolution of traits through natural selection. Altering these two values showed great differences in the traits that were observed in the future. If a trait started out reduced because of my controls, it was likely to continue to be reduced in the future. Ultimately, when these two principles work together, they can diminish a trait from the population even more quickly.

Works Cited

Darwin, C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life. New York: New American Library, 1963.

Gould, S. J. “The Evolution of Life on the Earth.” Scientific American, October 1994.

Grant, P. R. “Natural Selection and Darwin’s Finches.” Scientific American, January 1991

Weiner, J. The Beak of the Finch: A Story of Evolution in Our Time. New York: A. Knopf, 1994.