NATURAL SELECTION The ideas that shaped Darwin… Hutton, Lyell, Lamarck and Malthus Evidence of a Changing Earth Scientists Hutton and Lyell studied the organisms found in fossils. The older the fossil, the deeper it was buried Changes in the appearance of the organisms could be seen between layers. Lamarck’s Evolution Hypothesis In 1809, Lamarck proposed that an animal’s behavior could change the traits passed down to their babies. He thought, the more you use it, the more it grows. He did not know about how genes were passed down. Malthus’ Population Growth Population growth is limited by the resources available, such as food and living space. Once the food or the space starts to run out, then the growth rate will have to slow and then stop. Darwin’s Work Inherited Variation Slight mutations in the genetic code happen Before Darwin, scientists did not think this was important Darwin claimed that differences matter and can change the direction of a species Artificial Selection Nature provides genetic variation Humans often select for traits that they find most useful. Example: We like larger, sweeter tomatoes, so we will selectively breed plants for those traits. Struggle for Existence Species have to compete for the best food, living space and mates This drives the selection process Survival of the Fittest Organisms with the best adaptations for the environment will survive. These adaptations are passed down through the genes from parents to babies. The others will die off. Darwin called this, “Natural Selection.” Evidence for Evolution The Fossil Record There are many marine life fossils They saw many species with shells The shells got increasingly complex, suggesting evolution took place over time Homologous Body Structures Same bones, but different uses Mammal Examples: Human Arm w/Hand Horse Leg w/Hoof Whale Flipper Bat Wing Similarities in Embryos Types of Selection Directional Selection Individuals at one end of the curve are better fitted for the situation, so all shift. Stabilizing Selection Individuals in the middle of the curve are best fitted for the situation, so ends drop off. Disruptive Selection Individuals at either extreme are better fitted for the situation than an average individual. Genetic Drift Certain traits many become more common in a population by chance, rather than by a type of purposeful selection. Hardy-Weinberg Principle 1. 2. 3. 4. 5. There are 5 was to have a population at equilibrium (where there is no change) Random Mating Large Population No Movement into or out of the population No Mutations No Natural Selection The Process of Speciation Reproductive Isolation Only individuals of the same species can mate ? Behavioral Isolation Individuals could breed, but their styles of behavior or courtship make them not attracted to one another. Geographic Isolation Individuals could mate, but they are separated by distance Temporal Isolation Individuals could mate, but they naturally mate at different time periods. Process for the Evolution of Darwin’s Finches How Speciation Occurred… Founders Arrive: A few finches flew to one of the islands from South America and mated Separation of Populations: Some of these finches flew to a neighboring island Changes in Gene Pool: Adapting to new island Reproductive Isolation: Now the finches on the different islands are too different to mate! Ecological Competition: need food & nests Continued Evolution: natural selection continues Patterns of Macro-Evolution Extinction Species that cannot adapt to their environment will die out. Adaptive Radiation Many species evolve from a single species Convergent Evolution Some species look similar However, they are not closely related genetically Similar environmental factors cause the species to evolve in similar ways. Beaver Coypu Coevolution The process when two species evolve in response to changes in each other over time Example: Flowers change to keep attracting the bees needed to pollinate them.