Evolution & Natural Selection Part 2
Remember what we re talking about? Mechanisms of evolution: Mutation Genetic drift Migration Natural selection Artificial selection Sexual selection
Artificial selection A type of evolution where people are selecting for traits rather than nature The three conditions required for natural selection to occur are necessary here The results are the same; a change in the frequency of alleles in a population Now also doing it on a molecular level (biotechnology & GMO)
Artificial selection in animals
Artificial selection in plants Teosinte (wild corn) Modern cultivar corn
Sexual selection Same conditions apply... results: individuals with certain characteristics are more likely to get mates over others (usually) it is a female selecting a mate based on variation of phenotype
Sexual selection continued Leads to sexual dimorphism secondary sex characteristics not directly involved in reproduction plumage, manes, antlers, vocalizations, behaviors
One Extraordinary Example: The bower bird!
Remember what a theory is? an explanation that is very broad in scope, explains a great diversity of observations, & is supported by a large body of evidence the theory of evolution by natural selection explains a great diversity of observations & is supported by a large body of evidence
Evidence of evolution Geology Fossil record Biogeography Comparative anatomy & embryology Molecular biology Laboratory & field experiments
Geology Changes in the Earth s surface happen gradually over time: plates move rivers meander Islands are born Some changes can happen suddenly and dramatically
Fossil record Documents differences between past & present organisms & the fact many species have become extinct Incomplete
Biogeography Started by Alfred Wallace (independently defined natural selection with Charles Darwin) In the mid 1800 s he started biogeography: the The study of how species are distributed across the world AND more importantly how they got there! Observed how rivers and mountains often formed the boundaries between different species, conventional thinking indicated that within similar climates there should be similar selective pressures, leading to similar species but Wallace observed very different species in different geographical regions with similar climates made him go hmmmm??? 1876, The Biogeographic Distribution of Animals Alfred Wegner came along in 1915, and started thinking about plate tectonics and biogeographic distribution. Not until 1960 did we know the mechanisms of plate tectonics though
Comparative anatomy Anatomical similarities between species give signs of common ancestry Homologous structures: structurally similar features that have different functions Vestigial organs: structures of marginal or no importance to the organism; remnants of important structures in ancestors appendix in humans pelvic bones in whales molars in vampire bats
Comparative embryology Common embryonic development indicate the organisms share a common ancestor from which all have been modified
Molecular biology Since all living things share the same genetic code, this strongly suggests that all living organisms are related The more similar sequences between (or within) species, the more closely related the two organisms ex. siblings DNA sequences are more similar than unrelated organisms of the same species Identical twins? Identical DNA = Identical phenotype?
Laboratory & field experiments By choosing organisms with quick generation times/short life spans, it is possible to see evolution in action grass on golf course antibiotic resistant bacteria starvation resistant fruit flies guppies in Venezuela miniature dogs etc.
Next Time- a quick look at phylogeny