Objectives. Evolution. Darwin 5/30/2012. Pre-Darwin. Genetic change in a population over time.

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1 Objectives Evolution What is evolution? What lead Darwin to his thoughts 4 Premises of Evolution by Natural Selection Evidence supporting Evolution Genetic change in a population over time. Unifying concept of biology links all fields of life sciences into a unified body of knowledge Pre-Darwin Aristotle ( BCE) Scale of Nature moving towards perfection Jean Baptiste Lamarck ( ) Proposed that organisms change over time by natural phenomena vital force moved toward greater complexity over time could pass traits acquired during lifetime to offspring Charles Darwin ( ) Darwin made some observations!!!!! H.M.S. Beagle Based on observations: 1. Found similarities between organisms on Galápagos Islands and South American mainland 2. Observations of Artificial selection Darwin 3. Applied Thomas Malthus s ideas on human populations to natural populations 4. Influenced by geologists idea that Earth was extremely old 1

2 4 Premises of Evolution by Natural Selection resulting from Darwin s observations 1. Variation exists among individuals in populations. (and the variation is heritable) 4 Postulates of Evolution by Natural Selection 3. In a population not all individuals survive to reproductive age i.e., There are limits on population growth! - Organisms compete with one another for resources: food, living space, water, light - Predators, disease, weather 2. Variation that exists in population is heritable Thus, not all individuals survive to reproduce 4 Postulates of Evolution by Natural Selection 4. Differential reproductive success - Offspring with most favorable characteristics likely to survive and reproduce - pass favorable characteristics to next gen. Leads to accumulation of favorable traits in the population over generations Natural Selection Results in adaptations evolutionary modifications from environmental pressure improve chances of survival and reproductive success in a particular environment Over time accumulated changes in geographically separated populations can produce new species Important points to remember: 1. Differential reproduction 2. Evolution occurs in populations not individuals (but the environment selects traits at the individual level). 3. Mutation is important (provides genetic variation - synthetic theory of evolution) 4. Don t think of evolutionary change as purposeful - Panda s thumb Modern Synthesis Or synthetic theory of evolution combines Darwin s theory of evolution by natural selection with modern genetics - incorporates our understanding of genetics/dna Explains: why individuals in a population vary (genetic variation in a population) how species adapt to their environment 2

3 Evidence for Evolution?? Fossil Record Fossils Sedimentary rock layers occur in sequence of deposition Unicellular deeper than multicellular - simpler towards more complex - fossils show series of changes in many organsims Radioisotopes in rock accurately measure rock s age Transitional fossils: E.g., Whale Evolution Homologous Features: Similar features in different species. Natural selection modified for a particular function. Features Strongly derived suggests from the a common same structure ancestor in a common ancestor Homologous Features in Plants Analogous Structures Structural features that have similar functions that evolved independently i.e. they are not homologous structures!!!!! Result in convergent evolution organisms with separate ancestries develop similar adaptations in response to similar selective pressures (environments) 3

4 Analogous Features Fig a, p. 402 Vestigial Structures Nonfunctional/degenerate structures - were present and functional in ancestors organisms Evidence provided by Developmental Biology We note that gene mutations can affect events in development (snakes hind limbs) Development in different animals controlled by same kinds of genes indicates shared evolutionary history Biogeography: Past and present distribution of organisms Continental Drift Geographic distribution of organisms affects evolution (remember the environment selects traits) Isolated land masses contain organisms that evolved in isolation unique to those areas At one time, continents were joined to form a supercontinent Continental drift caused landmasses to separate played major role in evolution 4

5 Camel Pig Ruminants (cow, sheep, giraffe) Hippopotamus Cetaceans (whale, dolphin) 5/30/2012 (a) Cynognathus Lystrosaurus (b) Molecular evidence for evolution South America Africa India Australia Universal nature of genetic code Antarctica Only 4 nucleotides!!!!!!! 3 billion pairs in humans Human - chimp 95% same (c) Mesosaurus Glossopteris (d) Fig , p. 405 DNA Genetic Changes Genetic evidence Accumulation of genetic changes since organisms diverged Species A Species B Species C Amino acid sequences on proteins (cytochrome c) Artiodactyls Common ancestor of hippos and whales Can evolutionary hypotheses be tested experimentally? Hypothesis : based on DNA sequences Who is more closely related to who. Common ancestor of artiodactyls and cetaceans Fig , p

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