Transcript Evolution
Evolution Pre-AP Biology Charles Darwin Known as the Father of Evolution Wrote book On the Origin of Species Sailed the world on a ship called the Beagle Darwin Evidence for Evolution The fossil record – show biodiversity, mass extinctions and episodic speciation Geographic Distribution of Living Species – shows similarities among species living on different continents Homologous Body Structures – structures that have different mature forms but come from the same embryonic tissue. Similarities in Early Development – embryos of many vertebrates are very similar. Embryology Fossils and Evolution Natural Selection Over time natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness (ability to survive and reproduce) in its environment. Natural Selection causes struggles for existence and survival of the fittest. Natural Selection act on the phenotype rather than the genotype of a species. Gene Pools A gene pool is the combined genetic information of all the members of a particular population. A gene pool typically has two or more alleles for a given trait. Homozygous lethal traits can be carried by heterozygous individuals and thus remain in a gene pool. Relative Frequency is the number of times an allele occurs in a gene pool compared with the number of times other alleles occur. Microevolution is evolution on its smallest scale; change in the relative frequencies of alleles in a population over generations. What are gene pools? Sources of Variation Two main sources are mutations and gene shuffling. Mutations – changes in DNA sequence. These may or may not affect an organisms fitness. Gene shuffling – is the random shuffling of genes caused by sexual reproduction. Natural Selection on Single-Gene Traits Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. If the change is beneficial to the organism, the change may cause the original form to fade out and the newer organisms to be more fit and take over. Natural Selection on Polygenic Traits Natural Selection can affect the distribution of phenotypes in a population in any of three ways: directional, disruptive and stabilizing. The 3 selections Directional Stabilizing One phenotype is favored (Larger Beak) The average is best fit (Medium Beak) Disruptive Both extremes are favored (Small and Large) Can lead to separate species Directional Selection Directional Selection – Evolution causes an increase in the number of individuals with the trait at one end of the curve. Graph of Directional Selection Stabilizing Selection Individuals in the center of the curve and more fit and thus the curve narrows Graph of Stabilizing Selection Disruptive Selection Individuals at the ends of the curve are more fit than the ones in the middle causing two curves to form and possible new species to form. Genetic Drift In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. Hardy-Weinberg Genetic equilibrium takes place when allele frequencies remain constant. In order for genetic equilibrium to take place, five factors must remain true. 1. random mating 2. Large Population 3. No movement in or out of the population 4. No Mutations 5. No Natural Selection Hardy-Weinberg H-W Conditions Speciation Reproductive Isolation occurs when members of two populations cannot interbreed. At that point, they have different gene pools. Types of Isolation Behavioral Isolation – Two populations capable of interbreeding but have differences in courtship rituals or other types of behavior. Geographic Isolation – Populations are separated by geographic barriers such as rivers, mountains, or bodies of water. Temporal Isolation – Species reproduce at different times of the year. Speciation Galapagos Finches Speciation in the Galapagos Finches occurred by founding of new populations, geographic isolation, gene pool changes, reproductive isolation, and ecological competition. Survival Variation within a species help insure that some will survive major changes in the environment. Major diversity of species also insure that some of the species will survive major environmental changes. MACROEVOLUTION Evolutionary change on a grand scale, including the origin of new species and large scale evolutionary trends. Mass Extinction Mass Extinction means that MOST, but NOT ALL species went extinct during a short time period. Because of GREAT BIOLOGICAL DIVERSITY before a catastrophic event, some individuals of some species survive the event. Macroevolution Patterns Adaptive Radiation: When many species disappear, habitats and ecological opportunities are left open for survivors take over The result seems to be a burst of evolution that produces many new species For example, when the dinosaurs went extinct, that cleared the way for evolution of modern mammals and birds Let’s pretend that this is a small population of rhinos Macroevolution Patterns Macroevolution = large scale evolutionary changes Mass Extinction Adaptive Radiation Convergent Evolution Coevolution Punctuated Equilibrium Changes in developmental genes Mass Extinction Extinction occurs all the time: more than 99% of all species that ever lived on Earth are now extinct! Mass extinction = huge numbers of species disappear Mass extinctions extinguish species and also wipe out whole ecological systems It is difficult to determine the causes of mass extinctions, possibly volcanoes, continental shifts, changing sea level, asteroids? Mass extinctions often result in bursts of evolution producing many new species Adaptive Radiation A single species or a small group of species evolved into several different forms that live in different ways For example, Darwin’s finches When dinosaurs became extinct, it made way for adaptive radiation of mammals Convergent Evolution Groups of different (unrelated) organisms can undergo adaptive radiation in different places or at different times but in similar environments and natural selection may mold different body structures to look very similar So, unrelated organisms come to resemble one another Analogous structures = structures which look and function similarly, but do not share a common evolutionary history Coevolution Organisms that are closely connected to one another by ecological interactions can evolve together in response to each other’s changes over time For example, flowers and pollinators Punctuated Equilibrium Evolution can occur at different rates for different organisms at different times during Earth’s history: Gradualism = biological changes occur slow and steady or gradually over time Equilibrium = little or no change over time Punctuated equilibrium = new species produced by period of rapid change after long periods of equilibrium Can be due to isolation, genetic variation, mass extinctions, etc Phylogenic Tree A diagram that indicated probable pathway of evolution. Branches were species separate and form new species. The more branches shared, the closer the relationship. Review 1. 2. 3. Explain what happened to the gene pool of the moths color during the Industrial Revolution. What would you expect to happen to the color of the moths if natural selection did not act on color? Natural selection acts on the (phenotype/genotype). Genes only help pass on the traits.