THE WORK OF CHARLES DARWIN

EVOLUTION AS A (SCIENTIFIC) THEORY

• Evolution à change in a population of organisms over time

• Scientific Theory à well-tested explanation based on evidence that unifies as broad range of observations and hypotheses

• Law à has a mathematical equation to explain it

• Evolution is considered a theory as ALL evidence supports the idea that organisms have changed and continue to change, over time

CHARLES DARWIN• Lived in England (1809-1882)

• 1831-1836: Beagle’s five-year voyage mapping the coastline of South America

• 1859: On the Origin of Species by Means of Natural Selection

• EVOLUTION à explains how modern organisms evolved over long periods of time through descent from common ancestors

DARWIN’S VOYAGE

WHAT DARWIN KNEW

• What did Darwin (and science) know?• The Earth is REALLY old

• 4.6 Billion Years• The Earth has changed

over time• Mountains and valleys

formed• Rivers change course• Water erodes land

WHAT DARWIN KNEW• Humans can change organisms

through breeding• Organisms have rapid Population

Growth• Darwin realized most

organisms don’t survive and reproduce…

• He asked: Which individuals survive and why?

WHAT DARWIN DIDN’T KNOW

•DNA and Genetics• Knew that traits were passed from parent to offspring• Didn’t know HOW

• Most of what you learned last semester!

Acquired Characteristics

List the characteristics that you believe you have always had. For example, you may have brown eyes or curly hair.

Inherited Characteristics

List your acquired characteristics. For example, you may have learned how to play a musical instrument.

• Jean Baptiste Lamarck – first scientist to try to explain how organisms change over time

• Said that organisms could change during their lifetimes:

• By choosing to use or not use various parts of their bodies.

• individuals could pass these acquired traits onto offspring

parent mouseTail is removed

to simulate disuse of

characteristic during lifetime

offspring mouse

If Lamarck was correct, offspring would inherit

“acquired” trait of parent

= no tail

BUT offspring have tails

Lamarck was INCORRECT because:1. Organisms do not have an inner need to be perfect2. Evolution does not progress in a predetermined

direction3. Traits acquired by organisms during their lifetime

cannot be passed on to offspring

Lamarck gave us some good stuff too!• Lamarck was one of 1st to try to

explain evolution scientifically using natural processes

• Recognized link between organism’senvironment and body structures• Noticed that organisms were well

adapted to their environments

FOSSILS

• Fossils: preserved remains or markings left by organisms that lived in the past

• Sand and silt is eroded from land and settles in the bottom of bodies of water

• Layers pile up and form rock strata• Bodies get buried in layers

and become fossils• Fossils can also occur on land

under volcanic ash or dust

THE FOSSIL RECORD• Younger strata are layer on top of older

ones• Positions of fossils in rock strata can give

us relative age• Fossil Record: chronological collection of

life’s remains in the rock layers, recorded during the passage of time

• Fossils show that life on earth is changing

THE FOSSIL RECORD• Oldest fossil found: 3.8 billion years old• Fossils of extinct species help us reconstruct

the past• Fossil evidence supports cellular and

molecular evidence of Earth’s history• Whale fossils from 40 billion years ago show

that whales had hind-limb bones• Supports theory

that whales evolved from ancestors with 4 limbs

• Darwin noticed that some fossils of extinct animals were similar to living species

• Glyptodont – giant extinct armored animal àfound in area where current armadillo is found

• Armadillo = smaller living version of glyptodont

DARWIN’S FOSSILS