Possible Modes of Natural Selection Sexual- leads to differences in the sexes http://www.youtube.com/watch?v=gKybAp--n7M&list=PL2926D5AF798F9861&feature=share http://youtu.be/CYcs73oeFkc Diversifying/Disruptive- favors extremes over intermediates Directional- shifts the variation toward one extreme. Stabilizing- Leads to reduced variation, uniformity

Possible Modes of Natural Selection

Evidence of Evolution

Evidence of Evolution Fossil records Fossils are more then just bones Tracks Insects trapped in tree sap Impressions of leaves Animals buried in tar Fossils become more complex over time The age of fossils are determined by radioactive dating Carbon 14 – has a half life of 5,730 years Earth = 4.6billion yrs old Oldest fossils=bacteria traces 3.5billion yrs old

Evidence of Evolution

Nature's Whale Ancestors Evidence of Evolution Transition forms Skeletons showing animals that are similar but change over time and can be dated using radioactive dating and position in the rock layers. Nature's Whale Ancestors

Evidence of Evolution

Evidence of Evolution DNA and protein patterns If species have changed over time then their DNA should have also changed Thus more closely related species would have more similar DNA and amino acids Example of one amino acid sequence humans and chimps are identical, dogs have 91/104 identical and rattlesnakes have 84/104 identical

Evidence of Natural Selection Many species and locations Peppered moths experiment by Kettlewell

Evidence of Natural Selection Sickle cell anemia HH – normal / Hh - normal but low blood oxygenation / hh - sick with sickle cell 1/100 have sickle cell (hh) in central Africa 1/500 (African Americans)have sickle cell (hh) in the US Hh – reduces the risk of catching Malaria but makes it possible to pass sickle cell on to your offspring In the US it is directional selection against sickle cell In Africa it is balancing selection

Species Formation Ecological races are populations of the same species that differ genetically to adapt to their conditions

Species Formation Divergence is the increase of these differences over time At some point they may become a different species The different races of humans are extremely closely related genetically.

Two theories of evolutionary rates Gradualism Slow and steady over time Punctuated equilibrium Irregular rates Less transitional species