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Darwin’s Principles & Evidence of Evolution by Natural Selection AP Biology 2007-2008 Dodo bird Essence of Darwin’s ideas (1) Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations (5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to AP Biology the emergence of new species LaMarckian vs. Darwinian view LaMarck in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin AP Biology giraffes born with longer necks survive better & leave more offspring who inherit their long necks Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time AP Biology Fossil record A record showing us that today’s organisms descended from ancestral species AP Biology Anatomical record Homologous structures AP Biology similarities in characteristics resulting from common ancestry Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship AP Biology recent common ancestor Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for non-critical structures without reducing fitness snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone AP Biology This is not LaMarck’s loss from “disuse”! Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures? AP Biology Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc. AP Biology Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes Human/kangaroo Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships Nucleotide substitutions 100 75 Rabbit/ rodent 50 Horse/ donkey Llama/ cow Human/rodent Horse/cow Sheep/ goat 25 Pig/ cow Goat/cow 0 AP Biology Dog/ cow Human/ cow 0 25 50 75 100 Millions of years ago 125 Artificial selection Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties” “descendants” of wild mustard AP Biology “descendants” of the wolf Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective AP Biology Homework Explain 4 pieces of evidence supporting Darwin’s Theory of Evolution. For each one, give a specific example and make sure you explain WHY it serves as evidence for evolution. (could be in theme of paleontology, biogeography, embryology, comparative anatomy, molecular biology, etc.) AP Biology