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Transcript
EVOLUTION A bit of history on the theory of evolution Early theories (pre-1700’s) nature is seen as not changing and having originated through spontaneous generation Carolus Linnaeus was the first one to try to classify life (1735, placed us with primates) 1700’s an understanding of the age of the Earth develops through geology inheritance of acquired traits (use and disuse) ex. Baby giraffes are born with long necks because their parents stretched their necks to reach leaves (Jean-Baptiste Lamarck, 1801) Darwin and the Voyage of the Beagle in December, 1831’ Charles Darwin, a naturalist in his 20’s began a 5-year journey around the world on a ship called HMS Beagle Darwin’s role was to observe, record, and collect specimens of rocks, minerals, plants, and animals Darwin: PBS Darwin collected 1000’s of specimens and shipped them to England, mainly from South America and a chain of volcanic islands called Galapagos he collected them but did not realize what he was seeing until years later (ex. didn’t catalogue the finches very well, ate turtles that would later support his theories, etc.) Darwin spent the next 20 yrs analyzing his findings in light of artificial selection (ex. breeding of pigeons, breeding of dogs, etc.) Darwin’s Finches Arrival Success Competition Diversity & Opportunity Radiation How does evolution really work? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Hawaiian honeycreeper Natural Selection defined: The process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated. What is evolution? A theory that explains the origin of species At the genetic level, it is the theory of change in the inherited traits of a population of organisms through successive generations Or as Darwin would have put it: descent with modification from a common ancestor This modification or change through successive generations come from variation in a population Variation comes from mutations and genetic recombination (e.g. crossing over).; both can be passed on to the next generation Mutation refers to changes in a genomic sequence. E.g. For example, two chromosomes in the Homo genus fused to produce human chromosome 2; this fusion did not occur in the lineage of the other apes, and they retain these separate chromosomes. How do traits due to genetic variation become more common or rare? Two main processes are responsible: Natural selection and genetic drift Natural Selection as the Cause of Evolution - called “natural selection” because it happens on its own 1. Genetic Variation - there are many varieties of alleles - caused by random mutations - can be passed onto offspring (inherited variation) 2. Overproduction of Offspring - organisms make too many offspring 3. Struggle for existence - competition for limited resources 4. Differential survival and reproduction - only organisms that have certain characteristics will survive to reproduce - non-random, caused by the environment: amount of food, competition (ex. Darwin’s finches) Most of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown. Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population. Genetic drift In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. It happens to ALL populations—there’s no avoiding the vagaries of chance. Genetic drift is random – no adaptation