Natural Selection & Evolution Ch. 14 & 15 Biology Evolution Evolution is defined as the change in a population over time This is not a change in an individual (like weight loss) but in a population due to inherited factors A population is a group of members of the same species living in the same area, reproducing together Types of Evolution Macroevolution—how different species are related (and how new species can be created) Microevolution— evolution within a species (small group) “descent with modification” Kettlewell’s moths would be an example of this As evidenced by tracing homologous and vestigial structures Evidence for Evolution Fossil Record Law of supraposition Comparative Anatomy Homologous structures Vestigial structures Comparative Embryology Stages of fetal life Molecular Biology Gene sequencing Amino acid sequencing p. 304 Fossil Record Can tell us how old things are relative to other fossils Not everything makes a good fossil Not every environment is good for fossil preservation Gaps in the fossil record hold questions Because there is so much fossil evidence, it is basis for evolutionary thought Homologous Structures Show us how things may have evolved from one basic plan/blueprint geared toward a function Called descent with modification Vestigial Structures Can show us connections to other organisms with similar functional organs Can help us trace our evolutionary history (what we once were like) Ex: human tailbones http://www.livescience .com/11317-top-10useless-limbsvestigial-organs.html Comparative Embryology Can show us how a variety of organisms are more distantly related Even if they don’t look alike as adults, they may have stages as embryos/fetuses that show a common link/ancestor Molecular Biology Includes comparing the gene sequencing and amino acid sequencing of proteins of organisms to see how much they have in common This is one of the strongest types of evidence for evolution theory Cladograms A branched diagram representing ancestral relationships between organisms A visual evolutionary tree of life Is now often based on molecular biology evidence (gene and amino acid sequencing) Cladograms Macroevolution Gradualism Small amounts of change over a very long period of time Darwin’s theory (‘descent with modification’) Fossil record Punctuated Equilibrium Dramatically large amounts of change over a very short period of time Explains unusual gaps in the fossil record (dinosaur/asteroid) Gradualism vs. Punctuated Eq. Microevolution Convergent evolution When two populations living in similar conditions become more and more similar Cactus in deserts across the globe look similar due to similar conditions and survival needs Divergent evolution When two populations living in very different conditions become increasingly different Darwin’s finches that migrated to different coastal islands, all required slightly different beaks to get food Speciation The evolutionary process by which new species arise Species are groups of individuals that successfully mate together Can be due to a variety factors, either physical or behavioral barriers Geographic Isolation Reproductive Isolation Geographic Isolation When members of a group are physically isolated and therefore no longer reproduce together It can also be that the two subgroups are still physically close to each other, but do not interbreed due to subtle differences in their habitats Reproductive Isolation Temporal isolation: members have different breeding times Behavorial Isolation: members are not attracted to other members for mating Mechanical Isolation: the members are not physically able to mate Reproductive failure: members do mate and a pregnancy occurs/offspring is created BUT the offspring are sterile Darwin Wrote On The Origin of Species Is credited with the theory of natural selection as the primary way we explain how evolution occurs Shares partial credit with Alfred Wallace Darwin He was greatly influenced by his trip to the Galapagos Islands off the coast of S. America He collected many specimens and detailed notes/made diagrams His 20 years of data is why he receives more credit than Wallace Lyell’s book detailing how land forms gradually change over time (Principles of Geology) and Malthus’ essay On the Principal of Population describing how populations competed for food and shelter Both books impacted Darwin’s work Wallace Contacted Darwin about jointly presenting a paper describing the theory of natural selection He had arrived at the theory of natural selection independently (on his own) Darwin agreed so that he would not be forgotten in the development of this theory They both had taken trips to S. America and had read the same influential books Darwin receives more credit due to the detailed notes/evidence he had collected over many decades of study The Theory of Natural Selection Within every population exists variation Positive variations are called adaptations Individuals with beneficial adaptations live longer and therefore produce more offspring More offspring will show the beneficial adaptation in the following generations “Survival of the Fittest” Kettlewell’s Moths Kettlewell studied the effects of pollution on typically light colored trees on a moth population The moth population included light and dark colored moths Industrial Melanism The term describes how the moth population changed over generations to adjust to the changing tree color environment This ‘current’ example of natural selection in action added to the strength of Darwin’s argument (not just fossils as evidence) Types of Natural Selection Stabilizing selection—when the heterozygous condition is selected for and the extremes (homozygous) are selected against Types of Natural Selection Directional selection—when the population shifts toward one of the extreme (homozygous) conditions and away from the other Types of Natural Selection Disruptive (sometimes called sexual) selection— when the heterozygous condition is selected against and the extremes (homozygous) are selected for You decide! Other mechanisms of evolution Gene flow—a change in a population due to migration of individuals in and out of the area Non-random mating— how reproductive choices by individual members impact a population over time Genetic Drift-Bottleneck effect and Founder’s effect—how random chance impacts a small population Mutation—when a widespread genetic mutation impacts many members of a population (rare)
