Chapter 10 Outline The characteristics of the individual present in a POPULATION can change over EVOLUTION is an ongoing process time Darwin journeyed to a new idea Gradual changes in scientific beliefs in the 18th centuries helped shape Charles Darwin s thinking On a voyage around the world Darwin noted unexpected patterns among fossils and living organisms Fossils resemble but were not identical to living organisms in the same area And finch species on each of the Galapagos Islands differed from one another in significant ways These observations helped Darwin develop his theory of how species might change over time Four mechanisms can give rise to EVOLUTION EVOLUTION is a change in allele frequencies within a POPULATION It occurs by four different mechanisms MUTATION GENETIC DRIFT MIGRATION and NATURAL SELECTION MUTATION is an alternation of the base pair sequence in an individual s DNA If such an alternation changes an allele in an individual s gamete producing cells the frequency of alleles in the POPULATION changes and the POPULATION evolves MUTATION is the only way that new alleles can be created within a POPULATION GENETIC DRIFT is a random change in allele frequencies within a POPULATION unrelated to the alleles influence on reproductive success The effects of GENETIC DRIFT are most significant in small populations MIGRATION or GENE FLOW leads to a change in allele frequencies in a POPULATION as individuals move into or out of the POPULATION NATURAL SELECTION is a mechanism of evolution that occurs when there is heritable variation for a TRAIT and individuals with one version of the TRAIT have greater reproductive success than do individuals with a different version of the TRAIT Knowing the frequency of each allele in a POPULATION we can predict the genotypes and phenotypes we should see If there is a random mating and no EVOLUTION is occurring in a POPULATION recessive and dominant alleles do not change their frequencies POPULATION of organisms can become adapted to their environments FITNESS is a measure of the reproductive output of an individual with a particular phenotype compared with the reproductive output of individual with alternative phenotypes An individual s FITNESS can vary depending on the environment in which it lives ADAPTION refers both to the process by which organisms can become better matched to their environment and to the specific traits that make an organism more fit Although NATURAL SELECTION can produce ADAPTION it doesn t necessarily lead to organisms perfectly adapted to their environment Animal breeders and farmers undertaking ARTIFICAL SELECTION are making uses of NATURAL SELECTION when they modify their animals and crops through SELECTIVE BREEDING In DIRECTIONAL SELECTION the average value for the trait increases or decreases in STABILIZING SELECTION the average value of a trait remains the same while extreme versions are selection individual with extreme phenotypes have the highest fitness NATURAL SELECTION can change allele frequencies for genes involved in complex physiological processes and behaviors Sometimes a trait that has been selected for one function is later modified to serve a completely different function The evidence for EVOLUTION is overwhelming By analyzing fossil remains PALEONTOLOGISTS can reconstruct what organisms looked like a long time ago learn how organisms were related to each other and understand how groups of organisms evolved over time Observing geographic patterns of species distributions noting similarities and differences among species living in similar habitats and among species living in similar habitats but located far from one another helps us understand the evolutionary histories of populations Similarities in the anatomy and development of different groups of organisms and in their physical appearance can reveal common evolutionary origins All living organisms share the same genetic code The degree of similarity in the DNA of different species can reveal how closely related they are and the amount of time that has passed since their last common ancestor Replicated controlled laboratory selection experiments and long term field studies of natural populations allows us to watch and measure EVOLUTION as it occurs VISUAL REPRESENTATION