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Evolution, Natural Selection & Genetics of Species History of Evolution Darwin served as naturalist aboard the H.M.S. Beagle on a British science expedition around the world. He observed variation in related or similar species of plants and animals that were geographically isolated from each other. These observations were the basis for his ideas. Evolution • Changes in a species over time 1. Species become different 2. Descendants differ from their ancestors 3. New species arise from existing ones History of Evolution Darwin presumed that populations of individuals changed over time • In 1844, he developed the concept of evolution • Many years later that he published his idea “I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.” - Charles Darwin, "The Origin of Species“ Speciation • One species splits into two locations (geographic isolation) and over time becomes two different species. How Fast Does Evolution Occur? • Gradualism – Slow & steady change of one species into another – Small changes continually build • Punctuated Equilibrium – Rapid periods of evolution – Due to sudden environment change – Ex: Mammal diversity after dinosaur extinction Phylogentic Tree • Signify a change in speciation with regard to time Speciation • The formation of new species • As new species evolve, populations become reproductively isolated – Reproductive Isolation • Members of the same species cannot produce fertile offspring (due to separation of population) • Speciation in the Galapagos finches occurred by: – Founding a new population – Geographic isolation which led to reproductive isolation and changes in the gene pool due to competition for food Three Isolating Mechanisms • Behavioral Isolation – Capable of breeding but have differences in courtship rituals • Geographic Isolation – Separated by geographic barriers like rivers, mountains, bodies of water • Temporal Isolation – Two or more species reproduce at different times Donkey + Horse= Mule • Mule is sterile, so a donkey and horse are not the same species, since they don’t produce viable offspring. Tigon Result of male tiger and female lion mating inc aptivity. Offspring are infertile. Separated both geographically and ecologically. Liger Result of male lion and female tiger mating in captivity. Offspring are infertile. Four species of leopard frogs differ in their mating calls. Hybrids are inviable. These squirrels live on opposite sides of the Grand Canyon. This is an example of geographic speciation. Patterns in Evolution • Extinction = the elimination of a species • Extinctions occur continuously at a very low rate. – Occur at roughly the same rate as speciation – Usually affects a few species in a small area – Caused by local changes in environment Adaptive Radiation • Small population of one species differentiates into a variety of different species FOUNDER SPECIES Adaptation of Finch Beaks Adaptations Coevolution • Two or more species evolve together in response to changes in each other Coevolution • Can occur in beneficial relationships – Both species receive benefits from the other as a result of adaptations. • Coevolution can occur in competitive relationships – Sometimes called evolutionary arms race Convergent Evolution Describes evolution toward similar traits in unrelated species – Unrelated species with a similar environment • Faced similar evolutionary pressures Divergent Evolution Evolution toward different traits in closely related species – Cause = isolation kit fox red fox ancestor Different environments