Darwin’s Finches and Natural Selection by Cheryl Heinz, Dept. of Biological Sciences, Benedictine University, and Eric Ribbens, Dept. of Biological Sciences, Western Illinois University 1

The Galapagos Islands Located approximately 1000km from the coast of Ecuador, South America. This is just a little closer than the distance between Chicago and Philadelphia. –Mostly ground between the two U.S. cities. –Mostly deep water between the Galapagos Islands and the coast of South America. 2

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Implications Terrestrial species on these islands won’t have many relatives nearby. Neighboring islands will have close relatives –but new terrestrial species won’t arrive on these islands from the South American mainland very often. –most of the island species have had plenty of time to differentiate from their nearest living relatives. Another way of saying this is that there is very little gene flow between the islands and the mainland. –Gene flow = animals of the same species but a different gene pool are introduced into a population 4

CQ1: Limited gene flow means: A: Birds rarely move between the mainland and the islands. B: Birds on the island have the same genes as birds on the mainland. C: Birds on the mainland don’t like birds from the islands. D: Birds on the mainland won’t evolve, but birds on the islands might. 5

Charles Darwin Darwin explored these islands from April through October –Entire voyage of The Beagle: Dec Oct 1836 When and where he started thinking about what was to become his theory of evolution by natural selection. He did not publish his thoughts until the publication of The Origin of Species in

Charles Darwin’s Ideas Biological evolution is change in species over time. –This was not a new idea at the time –But there were no good mechanisms to explain how these changes occurred Natural selection is just such a mechanism, and this is what Darwin contributed. 7

Galapagos Endemics The Galapagos today is an amazing place. Animals live there that are found nowhere else on earth. –This makes them endemic –Perhaps the most famous of the endemic birds are the finches, of which there are 13 different species The islands are a natural laboratory, and one in which evolution can be observed. 8

Endemics Among the kinds of animals found here and nowhere else: –1 penguin species –1 giant tortoise species –1 marine iguana species –7 species of lava lizard –14 species of sea cucumber –1 species of sea lion –1 species of hawk –several species each of mockingbirds, doves, owls, flycatchers, and yellow warblers 9

The Finches The 13 finch species include: –6 species of ground finches –3 species of tree finches –1 woodpecker finch –1 vegetarian finch –1 mangrove finch –1 Coco Island finch A warbler finch that looks more like a warbler than a finch (one of the tree finches). The woodpecker finch actually uses cactus spines to dig grubs out of branches! 10

Evolution is: A change in the frequency of an allele, such as an allele for beak depth, is the basic definition of evolution. 11

Evolution by Natural Selection Steps: 1.Individuals vary in some traits. 2. Some of the differences in traits are passed along to offspring. –This requires a genetic basis to the trait –The trait is thus heritable (more…) 12

Evolution by Natural Selection 3. Different individuals produce different numbers of surviving offspring. –Produce different numbers, or –Different numbers survive. 4. The particular value of a trait is connected to the number of offspring produced. –Traits that allow for more offspring to be produced are said to be “naturally selected.” 13

Types of evolution Microevolution – changes in the gene (allele) frequencies in a population over a short period of time Macroevolution – changes in the gene (allele) frequencies in a population over a large amount of time that essentially differentiates a population from the rest of the species. 14

Evolution Changes in the population are due to 4 main mechanisms: –Mutation –Natural selection –Gene flow –Genetic drift 15