Darwin’s Theory of Evolution

What is a scientific theory?A well substantiated explanation

of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.

The Puzzle of DiversityEvolution

◦Change over time◦Change in the inherited

characteristics of populations over successive generations.

Evolution how◦Mutations that result in better

chance for survival Traits are passed on to offspring

The puzzle of diversityCharles Darwin

◦Largest contributor to current understanding of evolution

◦Voyage of the H.M.S. Beagle Collected samples of life in different parts

of the world.

◦Galapagos Islands Patterns of diversity Fossils

Voyage of the Beagle

Galápagos Islands

Galápagos SpeciesTurtles

◦ Different length necks◦ Different shells◦ Work perfectly for the island on which they live

Galápagos SpeciesFinches

◦ Different beaks◦ Different colors◦ Traits correlate to

environment

Artificial Selection

If we can change a species through our choosing, why could nature not choose and change?

Humans choose which organisms survive and reproduce

Thomas Malthus 1798

• Human populations will out grow space and food supplies.

• Can you see this theory at play today?

Natural SelectionSome organisms in the fight for life are better equipped than others

Those best equipped will survive

Natural SelectionSome organisms in the fight for life are better equipped than others

Those best equipped will survive

Natural Selection

Principles on pg 422

Ideas That Shaped Darwin’s ThinkingInfluences on Darwin’s Thinking

◦James Hutton (1785) Geological forces shaped Earth. Earth millions of years old, not

thousands.

How are mountains formed?

Tectonic Plates

Are Scientific Discoveries Unique?Alfred Russel Wallace

Influences on Darwin◦Jean-Baptiste Lamarck (1809)

Living things have changed over time ~ all species descended from other species.

Species are adapted to their environment.

Jean-Baptiste LamarckOrganisms acquired or lost

certain traits during their lifetime. These traits could be passed on to their offspring.

3 parts to this idea…

Tendency Towards PerfectionAll organisms seek perfection

Acquire traits that help them flourish◦Birds’ desire to fly led to flight

Use and DisuseChange parts of body through

use and disuse

Bird tries to fly, wings develop over time◦Bird does not fly, wings fall off over

time

Tie an arm behind your back…

Inheritance of Acquired TraitsGained during an organism’s

lifetime◦Body builders, strong heart, obesity

Traits passed directly to offspring◦Since I run a lot, my child will see the

advantage

Epigenetics?

EvaluatingLamarck was wrong; so, what did

he contribute?

Laid the foundation for evolutionary theory

First to document that organisms adapt to their environment

Influences on Darwin◦Charles Lyell – Principle of Geology

Past events must be explained using processes that can be observed.

Slow process ~ These processes are still occurring!

◦Robert Frost once said, “In three words I can sum up everything I

know about life: it goes on.”

Stop, collaborate, and listen…Could one person come up with

and completely legitimize a theory on his/her own?

Could Darwin have drawn the picture of Evolution all by himself?◦Who were four of the main

contributing artists to his first proposal?

Darwin Presents His CasePublication of On the Origin of

Species◦Inherited Variation◦Artificial Selection◦Natural Selection

Struggle for existence Fitness and Adaptation Survival of the Fittest

Natural Selection Descent with modification Common descent

15-3: Darwin Presents His Case

Publication of On the Origin of Species◦Evidence

Fossil record Geographic distribution Homologous body structures Vestigial organs Similarities in Embryology

Strengths and Weaknesses of Evolution