Aim: What are the most important theories on how organisms evolved? Important Evolutionary Theories! Aim: What are the most important theories on how organisms evolved?

Time Frame for Evolution Evolution does not progress in any set direction! Punctuated Equilibrium: Gradualism: - periods of stability interrupted by brief periods of change - slow, continuous change over time

CLADOGRAM: An evolutionary tree of life enabling us to compare relatedness through ancestry EXTINCT: Ends abruptly B Which 2 are most closely related? Why? Which letter represents the common ancestor of Birds and Amphibians? C D

Inherited Characteristics Acquired Charactersitics Make a list of your… Inherited Characteristics Acquired Charactersitics blue eyes Light skin tall Good public speaker Play the violin Funny Dancing skills

Lamarck’s Theory of Evolution Individual organisms develop new structures over the course of their lifetime because they need them in their environment Ex. Giraffes developed longer necks because they had to stretch to reach the trees Offspring will inherit this ACQUIRED characteristic Ex. Baby Giraffes are born with long necks b/c parents grew longer muscles

Weismann (disproved Lamarck) Experiment: cut off tails from mice bred the tail-less mice offspring had tails! • Conclusion: acquired traits are NOT inherited by the offspring, thereby proving Lamarck WRONG!

That would be as if… You work out… Become very muscular… And have a built baby!

Theory of Natural Selection (Charles Darwin) Introduced the idea that the environment / nature selects an organisms traits “Survival of the fittest” Organisms with adaptations better suited (favorable) for their environment will survive to reproduce more successfully than those without