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Overview: Students examine evidence for the relationship between UV and melanin in other animals; investigate the genetic basis for constitutive skin color humans; learn to test for natural selection in mouse fur color; investigate how interactions between UV and skin color in humans can affect fitness; and explore data on migrations and gene frequency to show convergent evolution of skin color. Author/Source: Smithsonian National Museum of Natural History Grade level: 13-16 Time: 7-10 50 minute class periods Teaching tips: These lessons were developed for AP biology students, but the level of the material is appropriate for college students. Concepts: Correspondence to the Next Generation Science Standards is indicated in parentheses after each relevant concept. See our conceptual framework for details. Biological evolution accounts for diversity over long periods of time. There is a fit between organisms and their environments, though not always a perfect fit. An organism's features reflect its evolutionary history. Similarities among existing organisms (including morphological, developmental, and molecular similarities) reflect common ancestry and provide evidence for evolution. Not all similar traits are homologous; some are the result of convergent evolution. Evolution results from natural selection acting upon genetic variation within a population. Natural selection and genetic drift act on the variation that exists in a population. Natural selection acts on phenotype as an expression of genotype. Phenotype is a product of both genotype and the organism’s interactions with the environment. Variation of a character within a population may be discrete or continuous. Continuous characters are generally influenced by many different genes. New heritable traits can result from mutations. Inherited characteristics affect the likelihood of an organism's survival and reproduction. Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing. Traits that confer an advantage may persist in the population and are called adaptations. The number of offspring that survive to reproduce successfully is limited by environmental factors. Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental. An individual’s fitness (or relative fitness) is the contribution that individual makes to the gene pool of the next generation relative to other individuals in the population. An organism’s fitness depends on both its survival and its reproduction. A hallmark of science is exposing ideas to testing. Scientists test their ideas using multiple lines of evidence. Scientists use multiple research methods (experiments, observational research, comparative research, and modeling) to collect data. Scientists can test ideas about events and processes long past, very distant, and not directly observable. Evolutionary trees (i.e., phylogenies or cladograms) portray hypotheses about evolutionary relationships. Teacher background: Genetic Variation Natural Selection

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