The following was modified from http://www.biologylabsonline.com/protected/EvolutionLab/
Objectives: EvolutionLab will allow you to study important principles of evolution by examining small populations of finches on two different islands,
"Darwin Island" and "Wallace Island." You will manipulate important ecological parameters that impose natural selection and then track how these ecological factors influence population size and the evolution of beak size.
This laboratory exercise mimics the kind of research that evolutionary biologists frequently do because evolutionary changes can take many generations to become apparent, and because it is not usually possible to experimentally alter ecological conditions on the scale necessary to observe evolution in larger organisms. When you have completed this lab, you should:
1. Understand the link between ecological selection factors and evolutionary changes in phenotype
2. Recognize the relationship among ecological factors, variation in phenotype, and variation in individual fitness
3. Understand how differences in ecological conditions between populations can lead to divergent evolution
Evolutionary biology is the study of the genetic, structural, and functional modifications of populations that occur from generation to generation through selection on individuals. Understanding how life evolves is a central concept in biology. The current diversity of organisms and the correlation of a species’ phenotype to its environment are the direct result of evolution that has occurred over very long periods of time.
The English naturalist Charles Darwin is generally recognized as the father of evolution through natural selection and sexual selection. Most of these theories continue to provide the basis for our current-day understanding and study of evolution.

Several years after Darwin's initial voyage to the Galápagos Islands, he developed several hypotheses that he felt explained how diverse species of tortoises and finches may have developed on the different islands. He realized that although the populations of these organisms could grow rapidly
(as each individual has many offspring), tortoise and finch populations did not increase in an uncontrolled manner; rather, the populations of these animals were somehow maintained in a relatively constant size. This indicated that, on average, each individual female only produces two surviving offspring. If some individuals have higher success, then other individuals must have lower or the population size would be increasing.
Darwin noted that individual organisms in a population varied in phenotype
(structure and function). He reasoned that if some individuals within a population were better suited to the environment (found food more quickly, escaped predators more easily, digested food more efficiently), they would be more likely to leave offspring compared to individuals with different phenotypes. The population would, over several generations, come to more closely resemble the type that had the better phenotype: it would be adapted to the environment.
Darwin named this force of evolution natural selection, to contrast it with the artificial selection that humans impose upon domesticated animals and plants. It is important to realize that while natural selection happens to individuals, the population can only be said to be evolving if there are the changes in the mean phenotype over time.
In the 1970s, the evolutionary biologist Doug Lowinton formalized the requirements for a population to evolve through natural selection, writing a paper with the following list:
1. There must be variation in phenotype among individuals
2. This variation must be heritable (passed from parent to offspring)
3. This variation must result in differences in fitness among phenotypes
If any one of these three components is absent – if there is no variation in phenotype (all humans are born with four limbs), or the variation that occurs is not heritable (tatoos), or if the variation that does occur does not alter fitness (blood type does not determine how many offspring a person has) – then natural selection cannot cause evolutionary changes in phenotype.

There are three modes by which the variation of a trait in a population can be influenced by natural selection: directional selection (average phenotype changes in a particular direction), stabilizing selection (variation in the trait declines but the average does not change; no evolution), and diversifying
selection (variation in the trait increases; most obvious as differences in mean trait among populations). These modes are discussed in the
Assignments sections of EvolutionLab.
Evolution is a central theme that unifies and connects virtually all disciplines of biology. However, because evolution occurs over long spans of time and is difficult to observe directly, the mechanisms that drive natural selection do not lend themselves to experimentation during a few hours or even a semester spent in the biology lab. In EvolutionLab, you will have the opportunity to simulate experiments in evolution to help you understand how traits of an organism can change in response to different biological and environmental conditions. You will study how beak size and population numbers for two hypothetical populations of finches on two different islands can evolve in response to ecological factors that you will manipulate by changing environmental conditions on these islands. EvolutionLab is not an exact simulation of finch beak evolution; rather it is a model designed to demonstrate important principles of adaptation by natural selection.
References
1.
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.
2.
3.
Grant, P. R. "Natural Selection and Darwin's Finches." Scientific
American, January 1991
4.
Weiner, J. The Beak of the Finch: A Story of Evolution in Our Time.
New York: A. Knopf, 1994.