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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: 9-12 Time: 7-10 50 minute class periods Teaching tips: High school teachers may want to pick and choose selected lessons within this sequence to use. Some lessons may be too challenging for a regular high school biology course. The more challenging lessons could be particularly useful in an AP biology course. 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. (LS4.A, LS4.D) There is a fit between organisms and their environments, though not always a perfect fit. (LS4.C) An organism's features reflect its evolutionary history. Similarities among existing organisms provide evidence for evolution. (LS4.A) All life forms use the same basic DNA building blocks. (LS4.A) Evolution results from selection acting upon genetic variation within a population. (LS4.B) New heritable traits can result from recombinations of existing genes or from genetic mutations in reproductive cells. (LS3.B) Traits that confer an advantage may persist in the population and are called adaptations. (LS4.B, LS4.C) Inherited characteristics affect the likelihood of an organism's survival and reproduction. (LS4.B, LS4.C) Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental. Natural selection acts on the variation that exists in a population. (LS4.B, LS4.C) Natural selection acts on phenotype as an expression of genotype. 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. (LS4.B, LS4.C) A hallmark of science is exposing ideas to testing. (P3, P4, P6, P7) Scientists test their ideas using multiple lines of evidence. (P6, NOS2) Scientists can test ideas about events and processes long past, very distant, and not directly observable. Scientists use multiple research methods (experiments, observational research, comparative research, and modeling) to collect data. (P2, P3, P4, NOS1) There is variation within a population. (LS3.B) The number of offspring that survive to reproduce successfully is limited by environmental factors. (LS4.B, LS4.C) Natural selection is dependent on environmental conditions. Evolutionary trees (i.e., phylogenies or cladograms) portray hypotheses about evolutionary relationships. Fitness is reproductive success - the number of viable offspring produced by an individual in comparison to other individuals in a population/species. Not all similar traits are homologous; some are the result of convergent evolution. Teacher background: Genetic Variation Natural Selection

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