Biology 203 Lab

Evidence of Evolution

Evolution - The change in allele frequencies over time in a population.

Gene - a segment of DNA that controls the appearance of a physical, behavioral or biochemical trait.

Allele - an alternate form of a gene.

Homologous - Similar in structure and evolutionary origin, though not necessarily in function.
                    Ex. The flippers of a seal and the hands of a human

Derived - formed or developed from something else; not original; differ from the ancestral skeleton.

The concept of evolution developed gradually, starting when philosophers recognized that populations produced more offspring than can possibly survive. The idea that organisms are competing for resources within their own species led to a further idea that any organisms with an advantage over its conspecifics would do better in the long run and would likely leave more offspring. If the advantage was heritable (could be passed on to the offspring), then that advantage would become more common in the population. That would mean that allele frequencies would shift, and the population evolves.

Charles Darwin, in 1858, published The Origin of Species : By Means of Natural Selection or the Preservation of Favored Races in the Struggle for Life. This work represented the first treatise on the subject of biological evolution, showing evidence of evolution primarily in artificially selected populations of animals such as cows and pigeons. Darwin explains how populations change when some individuals have an advantage (the favored races part) and thereby leave more offspring, leading to the concept of evolution.

Demonstrating evolution is relatively easy. The only requirement is that allele frequencies change, which can be determined by looking at the population over time and noting ratios of traits.

The classic example of evolution is the English peppered moth, Biston betularia. Museum collections of peppered moths show two color morphs that are genetically determined (traits are coded for by alleles and are heritable). The light colored morph was most common in the early collections, most likely because they were more cryptic against the lichen-covered tree trunks and branches. (Note: we have met all the requirements for natural selection to work: traits are heritable, there is variation, and some variants have an advantage.) However, the onset of the Industrial Revolution brought air pollution to England, producing coal smoke and soot, killing the lichens and coating the tree trunks. The light morph now showed up more than the dark morph, whose numbers began to increase.

Since then, air pollution laws have been passed in England, reducing the smoke production. Lichens have reappeared on the trees, which are no longer dark with soot. The light morph has reappeared and the ratio of light to dark is about what it was prior to the industrial revolution.