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Evidence for Evolution Topic 5.1 Evolution • Occurs when heritable characteristics of a species change over time *Characteristics acquired over a lifetime (such as blisters) are not heritable • Occurs through natural selection Evidence: Selective Breeding • Humans have been breeding plants and animals purposefully for thousands of years through artificial selection • The breeds of these animals greatly vary from their wild counterparts • Shows that selection can cause evolution Evidence: Fossil Record • The sequence of the fossil record matches evolutionary theory. – Older, simpler fossils are found in the bottom strata of rock layers – Newer, more complex fossils are found in the upper strata of rock layers Evidence: Fossil Record • Sequence of the fossil record matches theory: – Plant fossils appear on land before animal (herbivores) fossils do – Some sequences of fossils are known • Link together common ancestors • Predicts close living relatives accurately Evidence: Homologous Structures • Homologous structures are structures in different species that may look different, perform different functions but have a common structure and common origin. – Ex: forelimbs in humans, cats, whales and bats Pentadactly limb: Forelimb • Homologous structures are not to be confused with analogous structures – Analogous structures have similar functions and may have similar shapes, but do not have a common origin. – They have evolved independently of each other Evidence: Patterns of Variation • If populations gradually diverge over time, we should be able to see examples of populations in different stages of divergence – Variation within a species that is recognizable, but not enough to be considered a different species. • Peppered moths (Biston betularia) have natural variation in their wing colors – Melanic: dark colored wings (morpha: typica) – Non-melanic: light colored wings (morpha: carbonaria) • Peppered moth populations in pre and post industrial England Explain the trends seen in the graph above Evidence: Speciation • Populations of a species can gradually diverge into separate species by evolution – Speciation occurs when a population becomes separated into two or more groups and are cut off from breeding with each other. • Over time each group will evolve in different ways, creating distinct characteristics. • If the two different populations can no longer successfully breed with each other, they have speciated into two distinct species. *Speciation occurs often on islands where species are geographically isolated. • These populations are endemic: only found in a distinct geographic areas. Evidence: Speciation • Geographical distribution of species matches the idea of gradual speciation *Different species of mockingbirds are distributed in the galapagos islands suggesting the main island was populated first and outlying islands populated from the main island species then speciated.