Darwin’s Theory of Evolution

16.3 and 16.4

Natural Selection• The process by which organisms with

variations most suited to their local environment survive and leave more offspring.

• Operates like artificial selection, but occurs IN NATURE.

When Does Natural Selection Occur?

1. When more organisms are born than can survive (the carrying capacity has been reached).

When Does Natural Selection Occur?

2. When there is natural heritable variation and adaptation.

An adaptation is a heritable characteristic that increases an organism’s ability to survive.

When Does Natural Selection Occur?

3. There is variable fitness among individuals.High fitness- adaptations suitable to the

environment, can survive and reproduce.Survival of the fittest

Common Descent: Evolutionary Trees

Evidence That Supports Evolution Theory

F- fossilsA- anatomical structuresM- molecular evidenceE- embryological evidence

Support for Evolution 1: Fossils/Age of Earth

• Earth is 4.5 billion years old according to radioactive dating.

• Paleontologists have recently discovered fossils that form a series that traces the evolution of modern species from extinct ancestors.– Examples: whales from land mammals, birds from

dinosaurs, fish from four-legged land animals.

Types of Whales

Whale Evolution Theory

Support for Evolution 2: Anatomical Structures

• Homologous structures are shared by related species and have been inherited from a common ancestor.– Results from descent with modification from a

common ancestor.

Analogous Structures• Analogous structures are body parts that

share a common function, but not structure.

Vestigial Structures• Vestigial structures are inherited from

ancestors but have lost much or all of their original function due to different selective pressures.– Example: hip bones in dolphins

Support for Evolution 3: Molecular Biology

• Universal genetic code and homologous molecules.

• Examples: cytochrome c, Hox genes

Support for Evolution 4: Embryology

• Similar patterns of embryological development.

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Testing Natural Selection• This is difficult because evolution takes

millions of years. • Peter and Rosemary Grant have spent 35 years

studying the Galapagos finches.– Natural selection takes place in wild finch

populations frequently and sometimes rapidly.– Variation within a species increases the likelihood

that the species can adapt to and survive environmental change.

Modern Example of Evolution: Antibiotic Resistance and Superbugs

Bacterial Conjugation