Evolution Chapter 25 Great Idea: All life on Earth evolved from single-celled organisms by the process of natural selection.

Chapter Outline The Fact of Evolution Chemical Evolution Natural Selection and the Development of Complex Life The Evolution of Human Beings

The Fact of Evolution

Evolution –Ongoing process of change Scientists accept evolution as fact –Debate various theories

The Fossil Record Fossils –Organism’s hard parts preserved Turned to rock Replaced by minerals –l Fossil record –Fossils found, catalogued & analyzed –Shows transitions –Incomplete Three key ideas –Older fossils more different –Increasing complexity with time –Most species have gone extinct

The Biochemical Evidence DNA –Evidence for evolution –Changes slowly –Also compare amino acid sequences Cytochrome C –Humans and chimps identical –Rattlesnake 86% overlap

Evidence from Anatomy: Vestigial Organs Vestigial organs –Internal features –No useful function Example –Appendix: humans –Wings: penguins –Hind legs: whales

Chemical Evolution

Chemical evolution –Process of combining rocks, water and gases Miller-Urey experiment Formation of cell –Still unknown

Black Smokers –Deep-ocean floor –Vents of mineral rich hot water –Diverse ecosystem Most primitive bacteria Hydrothermal zones –Site of life’s origin? Protected Ideal chemical environment

RNA Enzymes Early life was simpler –RNA catalyzed reactions –Created proteins –Proteins led to DNA

The Window of Opportunity Chemical processes –Occurred rapidly Recent discoveries –Schopf Evidence of life 3.5 billion years ago First Cell – billion years ago

The First Cell First cell –No competition –Multiplied rapidly Special characteristics –20 amino acids

Natural Selection and the Development of Complex Life

Natural Selection Darwin Natural Selection –Variation in populations Some variation heritable –More individuals born than will survive Adaptation Artificial selection

The Story of Life First cell –Natural selection mutations Mutations –Most not beneficial Environment –Impacts evolution Eukaryotes Colonies Hard Shell –Cambrian explosion

Geological Time

Mass Extinctions and the Rate of Evolution Rate of extinction –10%-20% extinct in 5-6 million years Mass extinctions –30%-90% extinct Mechanisms –asteroid Evolution –Gradualism –Punctuated equilibrium

The Evolution of Human Beings