THE SAGA OF THE PEPPERED MOTHS: Population Genetics Lab
Adaptation is critical to specle's survival. Natural selection, the process by which organisms change over generations, is the primary mechanism by which species adapt. However, people often think that animals consciously adapt to their environments - that the peppered moth can change its color, the giraffe can permanently stretch its neck, and the polar bear can turn itself white - all so that they can better survive in their environments. In reality natural selection states that individuals with certain heritable traits leave more offspring than others and thus the genes of those individuals survive. Every population has a reserve of alleles or its gene pool. A gene pool is defined as the sum of alleles in a population at any one time and contains the variation to produce different phenotypes on which evolution can act.
Natural selection is often simplified to "survival of the fittest". Fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals. The more genes you pass on to the next generation the fitter you are. Therefore fitness is more than just the ability to run quickly or fight off competitors. In today's lab you will explore some of the evidence for evolution and will examine a few of the mechanisms through which evolution acts.
The saga of the pepper moth (Biston betularia) and it's response to industrial pollution in England is a well known example of selection in natural populations. The pepper moth is found in two forms (or "MORPHS"): a mottled form and a dark-colored melanic morph. During the mid 1800s, the mottled form predominated the countryside near Manchester, England; making up better than 99 percent of the population. By 1898, however, the situation was reversed, with the melanic (dark) form comprising the greater percentage of the population: Researchers noted that the spread of the melanic form paralleled an increase in industrial pollution which caused the bark of trees to darken. Examine Figure 1 below:
Why do you think the peppered moth population changed after England's industrial revolution?
