EVOLUTION? Modern Clues Martin

Evidence: Fossils Fossils show: Life has changed over time More than 99% of all organisms that have ever lived are extinct now Martin

What can fossils tell us? Provide models of what life may have looked like Provide clues to lifestyle: Family groups Foods Environment Provide clues to evolutionary relationships among organisms Martin

Gaps in the Fossil Record Incomplete record Most organisms do NOT become fossils We have NOT found all fossils What we DO know: Simpler forms of life existed early in Earth’s history More complex forms of life appeared later Martin

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Evidence: Embryology Embryo: the earliest growth stage of an organism Embryology: the study of these early growth stages Human embryo at four weeks: Martin

Vertebrate Embryos The embryos of fish, reptiles, birds and mammals are similar (tail, gills or gill slits) This suggests an evolutionary relationship: common ancestors http://www.pbs.org/wgbh/evolution/library/04/2/quicktime/l_042_02.html Martin

Evidence: Homologous Structures Populations evolve to adapt to a particular environment Structures with similar origins are homologous Martin

Homology= similar origin but adapted for different functions Analogy+= similar functions, but evolved from different origins Martin

Evidence: Vestigial Structures Vestigial structures: structures that no longer seem to have a function Manatees, snakes, and whales no longer have legs, but still have hip bones Vestigial structures may once have functioned in an ancestor Martin

Evidence: DNA Recall: Found in genes, located on chromosomes Scientists compare DNA to identify similarities between organisms By looking at DNA, scientists can determine how closely related two organisms are Example: DNA studies that dogs are the closest relatives of bears Martin

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Evidence: DNA Humans 23 pairs of chromosomes Apes: 24 pairs of chromosomes—but when two of an ape’s chromosomes are laid end-to-end, a match for human chromosome number 2 is found Humans and apes make similar proteins, such as hemoglobin, the oxygen-carrying protein in red blood cells Martin

Putting it All Together http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Martin