Change over Time

Chapter 2 Lesson 3

What is natural selection?

population - all the members of the same species living in the same geographic area

variations - differences among members of the same species

Charles Darwin - developed the theory of organisms changing over time

Natural Selection - Darwin’s theory that organisms pass on traits that help them survive in their environment. “Survival of the Fittest”

extinct speciesno longer exists on earth

Critical Thinking Questions

How do insects become resistant to chemicals that farmers use to kill them?

How does natural selection explain how organisms change over time?

What is evidence of change over time?

Fossils - any remains, traces, or imprints of organisms that lived long ago

— trapped in tree sap

—- wet footprints covered by sediments

How Fossils Form

— tar pits

—bones of the animal harden into rock

What fossils tell us - provide clues that tell us how environments change

Shark teeth fossils found in Tupelo, Mississippi mean that Mississippi was once under an ocean.

- determine past climate of an area

Plant fossils found in Antartica mean it once was a warm environment.

- what organisms were like in the past and how they have changed

Smilodon is the ancestor of the tiger. The teeth are smaller now. What does this mean?

Critical Thinking Question

How do fossils provide clues that show how life and environments have changed?