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

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

• Fossil record– Fossils found, catalogued, and analyzed

– Shows transitions– Incomplete

The Fossil Record – cont.

• Three key ideas– Older fossils more different– Increasing complexity with time– Most species have gone extinct

Wide Variety of Fossils

Fossil Trilobites

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

• Examples– Appendix: humans– Wings: penguins– Hind legs: whales

Wings of a Penguin Are Vestigial Organs

Chemical Evolution

Chemical Evolution

• Chemical evolution– Process of combining rocks, water and gases

• Miller-Urey experiment• Formation of cell

– Still unknown

Miller-Urey Experiment

Black Smokers

• 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

Black Smokers

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– 4.0-3.5 billion years ago

The First Cell

• First cell– No competition

– Multiplied rapidly

• Special characteristics– 20 amino acids

Science by the Numbers

• Cell division

The Ongoing Process of Science

• Did life also originate on Mars?– Evidence from a meteorite

Natural Selection and the Development of Complex Life

Natural Selection

• Charles Darwin

• Natural Selection– Variation in populations

•Some variation heritable

– More individuals born than will survive

• Adaptation

• Artificial selection

Dog Breeds

Cobalt-Winged Parakeets

Science in the Making

• The reception of Darwin’s theory– On the Origin of the Species

• Alfred Russell Wallace

Charles Darwin

The Story of Life

• First cell– Natural selection

•Mutations

• Mutations– Random– Most not beneficial

• Environment– Impacts evolution

The Story of Life – cont.

• Eukaryotes• Colonies• Hard shell

– Cambrian explosion

A Fossil Microbe

Rock with Fossils

Major Steps in the Evolution of Life

Geological Time

The Ongoing Process of Science

• The evolution of whales– What does the fossil record tell us?

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

Extinction Events

Giant Crater near theYucatan Peninsula

Chesapeake Bay Impact Drilling Site

The Evolution of Human Beings

“Lucy”

Neanderthal Man

Thinking More about Evolution

• Young-earth creationism

• Intelligent design