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EVIDENCE SUPPORTING EVOLUTION Fossil Evidence & Biogeography Homologous & Analogous Structures Vestigial Structures Embryology Molecular Comparisons Microevolution in Action Paleontological Evidence (The Fossil Record) A record of all fossils ever discovered which demonstrates the changes in organisms’ structures over time Transitional forms (missing links) have been found to show relationships between ancient forms and modern ones Fossils can be dated radioactively to determine their age accurately http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html Biogeographical Evidence: Convergent Evolution Unrelated species living in different regions of the world with similar environmental features happen to look alike (analagous) Supports natural selection concept: adaptation to environmental factors Biogeographical Evidence Example: Unrelated anteaters around the world share common features because of their common selective pressures (food, climate, etc…) Comparative Anatomy Homologous Structures Structures on different species which are similar in form, but different in function Structures indicate a shared common ancestor Example: The arm bones of various vertebrate organisms Homologous Structures Comparative Anatomy cont… Analogous Structures Features that share identical functions and look similar in build due to natural selection Internal anatomy is very different; organisms are not closely related Examples: bird and insect wings (i.e. hummingbird & hummingbird moth) Vestigial Structures Structures that remain on an organism which have no purpose, or are not used for their original purpose anymore Examples: Whale/snake hip bones Ostrich wings Human tailbone,wisdom teeth, appendix Whales have a pelvis (hip bone) and a femur (upper leg bone) but they have no need for them in the water Flightless birds, like this Cassowary and Ostrich have vestigial wings The human tailbone or coccyx doesn’t do much for us – except hurt if you land on it. These are left-overs from ancestors who used tails for balance or communication like many mammals do today. Some children are born with a full tail (since we have the genes for it). Those who have had to have it surgically removed don’t suffer any negative health effects without it. Human wisdom teeth: the rear molars that most (but not all) people must have removed when they grow in right around age 18. Left-overs from a larger mouth or a byproduct of better modern hygiene? The human appendix: a vestigial organ that is still used by other, mostly herbivorous mammals to help them digest plants in their diet. It is thought to be a leftover from ancestors with a more herbivorous diet. Now it is more a nuisance than anything. They commonly become infected causing appendicitis and must be surgically removed. Embryological Evidence Embryos of a different organisms look extremely similar at early stages of development -similarities begin to fade with further development Molecular Evidence Organisms share a great deal of the same DNA or proteins The closer an organism is to it’s ancestor, the more molecular similarities exist Humans/Chimps = 98% the same DNA Blood proteins in humans & gorillas differ by only one amino acid! Some genes are almost identical in most of the animal kingdom One organism’s molecular sequences can work in another organism Human DNA can make yeast work! Evolution in Action Kettlewell’s Moths: England’s industrial revolution killed tree lichen and added soot to trees, allowing the population of peppered moths to shift in favor of the black variety (previously rare mutation) Evolution in Action: Speciation Divergent Evolution Darwin’s Galapagos Finches
