Evolution and Natural Selection Peekskill High School Biology by: First-name Last-name
2 Charles Darwin Darwin explored these islands from April through October 1835. Entire voyage of The Beagle: Dec 1831 - 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 1859.
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. 3
Natural Selection In any population of organisms there is natural variation. Some of these variations will allow the organisms possessing them to survive and reproduce better than those without these particular traits.
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. 5
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. 6
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! 7
8 Seeds A variety of seeds are produced on the island. Finches prefer the softest seeds, which are the easiest to open. The seeds above are seeds of a plant called Caltrop, in the genus Tribulus. These are among the hardest to eat. It takes a medium ground finch with a beak at least 11mm long to open one. Ground finches with beaks that are 10.5mm long or less haven t even been seen trying to eat them.
9 Heritability It s important to note that beak size and shape is heritable in these finches. A bird with a large, deep beak will have offspring with large and deep beaks. Natural selection can occur without heritability, but evolution by natural selection cannot!
10 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 )
11 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.
Natural Selection Competition If there are not enough resources for all of the individuals, there will be competition for those resources. Survivors represent a small part of the individuals produced each generation.
Natural Selection Populations Show Variation Which individuals will survive is often not a matter of luck. Populations show variation individuals are not identical. They differ in many different traits.
Natural Selection Variation is Heritable Some of the variation between individuals in the population is heritable. It can be passed down from one generation to the next.
Upsetting Genetic Equilibrium Natural selection is not the only way that allele frequencies can change from one generation to the next. Genetic Drift a random loss of alleles. Mutation a new mutation can add alleles. Nonrandom mating inbreeding increases the number of homozygous traits. Migration shuffles alleles between populations; can prevent speciation.
Summary
Resources Upper Saddle River, N.J. Biology: Pearson/Prentice Hall, 2008. https://www.google.com