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Transcript
Charles Darwin • Born 1809 in England • Naturalist of the H.M.S. Beagle • Through his travels he made numerous observations that led him to propose a theory of how life changes over time. Darwin’s Voyage Darwin’s Observations & Influences • Patterns of Diversity seemed to rely on the environment. • Darwin collected numerous fossils, some of which were of species no longer seen. • Geologist James Hutton: geological changes of Earth • Charles Lyell: Geology suggests the earth is extremely old. • Jean Lamarck: selective use of organs led to certain traits and these traits were passed on to offspring. Darwin’s Finches Artificial Selection • Humans select the genetic variations that are desired and breed organisms with that trait in order to produce offspring with the desired trait. • Examples: Horse breeding for speed Agricultural scientists using plants to develop new vegetables Meat producers breeding for lean meat Evolution by Natural Selection • Darwin was convinced that artificial selection works in nature. – Competition for resources – Predators that are faster or better equipped will win in competition. – Survival of the Fittest: Those best adapted to their environment will survive, reproduce and pass on their traits to their offspring. – Over time, natural selection will result in a population of organisms that have traits that make them better suited for survival. Natural Selection • Cannot be seen in one individual. • Can only be observed as changes in a population over many generations. Evidence of Evolution (Change over Time) • • • • The Fossil Record Homologous body structures Similarities in Embryology DNA analysis Fossils • Remains of ancient life, formed at different times during Earth’s history. • Fossils document that life on Earth has changed over time. • 99 % of all species that have ever lived on Earth have become extinct (they no longer exist). • Imprints of dead organisms in rock. How are Fossil dated? • Relative dating – the age of the fossil is determined by comparing its placement with the placement of fossils in other layers of rock. The lower layers are older than the upper layers. • All living things are mostly made of carbon. • A small portion of this carbon is in the form of Carbon14, an unstable radioactive isotope. • Once an organism dies, the C-14 in the organism begins to disintegrate. Because it disintegrates at a steady, known rate, scientists can measure the amount of C-14 remaining and use a scientific formula to determine the age of the sample. • Half-life: the length of time for half of the radioactive atoms in a sample to decay. C-14 has a high life of 5730 years. For rocks older than 60,000 years, potassium-40 is used. It has a half life of 1.26 billion years. Homologous structures Structures that are constructed from the same bones, yet have different functions. Homologous vs. Analagous Structures Embryonic Development Comparisons The same groups of embryonic cells develop in the same order and in similar patterns to produce homologous structures. Vestigial Organs • Organs with little or no function. • May have been organs used in ancestors, but no longer needed to survive or reproduce. • Examples: Human appendix, legs on skinks, hip bone in whales Founders effect • Founder effect – change in the allele frequencies as a result of the migration of a small subgroup of a population • Speciation in the Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population’s gene pool, reproductive isolation and ecological competition. • Members of a sexually-reproducing species are able to interbreed, produce fertile offspring, and have a shared gene pool • Gene pool refers to the collective group of alleles of all the individuals in a population • Different species do not exchange genes with each other by interbreeding Speciation • Speciation - Formation of a new species. • Speciation is the final result of changes in gene pool allelic and genotypic frequencies • Isolation – Behavioral isolation (can mate, but do not due to behavior) – Geographic isolation (separated by barriers) – Temporal isolation (reproduce at different times) • Natural selection on single-gene traits lead to changes in allele frequencies and therefore evolution. Variation and Gene Pools • Gene Pool - All genes that are present in a population. • Evolution is any change in the relative frequency of alleles in a population. • Variation is the raw material for evolutionary change • Features that make an organism suited for its environment so it can survive, reproduce, & pass its alleles onto its offspring are called adaptations Genetic Drift Genetic drift refers to changes in allele frequencies of a gene pool due to chance (random) events Sources of Genetic Variation –Mutations –Gene shuffling (crossing over during meiosis) –Polygenic traits Macroevolution Large scale patterns of change over long periods of time. • Extinction – disappearance of a species • Adaptive Radiation – a single species evolved into several different species • Convergent evolution – unrelated organisms evolve similarities when adapting to similar environments • Coevolution – two species evolve in response to one another • Punctuated equilibrium – long stable periods are interrupted by brief periods of rapid change Cladogram – diagram that shows evolutionary relationships among a group of organisms