Important Evolutionary Theories Aim What are the most

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! • Gradualism: - slow, continuous change over time • Punctuated Equilibrium: - periods of stability interrupted by brief periods of change

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

Make a list of your… Inherited Characteristics • blue eyes • Light skin • tall Acquired Charactersitics • 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