Experimental Report for Evolution Lab, Essay Example

Introduction

According to Charles Darwin’s theory of natural selection, traits are passed down over time when they allow a species to both survive and reproduce. The mixture of traits that are inherited as a consequence of this phenomenon contributes to a process known as evolution, which allows species to slowly change over time. Ultimately, this results in extinction species who are unable to adapt or divergence of species that adapt to the environment in different ways.

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. During the island’s history, a broad array of food was available. After an environmental event, the finches were forced to find food in locations with low levels of competition. Therefore, some birds would eat small soft seeds and others would eat hard seeds. Birds with small beaks were more efficient ateatingthe small soft seeds and birds with large beaks were more efficient at eatingthe large hard seeds.Because birds that were able to compete for food effectively survived and were able to reproduce while the others died, these birds evolved in a manner that allowed more efficient food consumption in periods of food shortage.

Darwin stated that for a trait to evolve through natural selection, it must affect survivorship and reproduction. However, the Galapagos finches example emphasizes that different traits must be present in the population in order for selection to occur. I hypothesize that variation must exist among individuals for traits to be heritable.

Experimental Design

To determine how a trait is heritable and can therefore evolve through natural selection, beak size and variance were kept constant for Darwin and Wallace Island, in addition to clutch size, island size, and precipitation. However, the heritability was changed to to 0.70 on Darwin Island and to 0.4 on Wallace Island. Wallace Island therefore served as a control population in which evolution was occurring more slowly.The results were recorded after the population was left for 100 years.

To determine how a trait must have variation among individuals for a trait to evolve through natural selection, beak size, clutch size, island size, and precipitation were kept constant between the two islands, but variance was changed to 2.0 for Darwin Island and to 0.5 for Wallace Island. It was expected that the finches on Darwin Island would evolve more rapidly, as Wallace Island was used as a control population. The results were recorded after the population was left for 100 years.

Figure 1 shows that the decreased 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 difference occurs in 2090, indicating that beak size continues to diverge over time. Ultimately, when a trait is inherited less frequently, it is less likely to contribute to the population’s genetics.

Figure 2 shows that there is a major difference between the beak size of the birds on Wallace Island and Darwin Island, beginning with when the variability was selected. The birds on Darwin Island were given a wider range of beak size, which allows larger beaks to continue to be inherited into the future, while the birds on Wallace Island were given a smaller beak size so this phenomenon did not occur. 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 after leaving the population for a century. If a trait started out reduced due to my controls, it was likely to continue to be reduced in the future. Ultimately, when reduced inheritance and variability are induced in the population, evolution occurs 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.