EVIDENCE OF EVOLUTION

Key Concepts

• What evidence supports the theory of evolution?

• How do scientists infer evolutionary relationships among organisms?

• How do new species form?

Key Terms

Homologous Structures– Body parts that are structurally similar

in related species.

Key Terms

Branching tree– A diagram that shows how scientists

think different groups of organisms are related.

Identifying SupportingEvidence

• Identifying supporting evidence helps us understand the relationship between the facts and the hypothesis.

• Evidence consists of facts that can be confirmed by testing or observation.

Supporting Darwin’s Theory

• Fossils show that organisms that lived in the past were very different from organisms alive today.

• Patterns of early development show that some different organisms look similar during their early stages.

• Similar body structures in different species show that the organisms shared a common ancestor.

Interpreting the Evidence

• FOSSILS

• EARLY DEVELOPMENT

• BODY STRUCTURE

FOSSILS

• The preserved remains or traces of an organism that lived in the past.

• Fossils show that organisms that lived in the past were very different than organisms alive today.

• Scientists use fossils to infer the structures of ancient organisms.

EARLY DEVELOPMENT(embryology)

• Scientists compare the early development of different organisms to make inferences about evolutionary relationships.

• Similarities in early development among different organisms suggests that they are related and share a common ancestor.

BODY STRUCTURE(homologous structures)

• Darwin compared body structures of living species when observing the species on the Galapagos Islands.

• Body structure is an organism’s body plan, how its bones are arranged.

• Similarities in body structure provide evidence that organisms evolved from a common ancestor.

Species Relationships

• Fossils, early development patterns, and body structure provide evidence that evolution has occurred.

• Scientists also have used these kinds of evidence to infer how organisms are related to one another.

New Evidence

• DNA

• Protein Structure

Similarities in DNA• Scientists compare the

genes of different species to determine how closely related the species are.

• The more similar the sequence of bases in the DNA, the more closely related the species are.

• The more similar the order of amino acids (codes for proteins) in the DNA, the more closely related the species are.

Combining Evidence

• The use of DNA and protein structure has confirmed conclusions that scientists had already based on fossils, embryos, and body structure.

• The use of DNA and protein structure has also caused scientists to “revise” the branching trees of some species.

Branching Trees

• Branching trees show common ancestry (phylogeny).

• Evolution is about gradualism and phylogeny.

How Do New Species Form?(speciation)

• A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits.

• Isolation/Separation– River– Volcano– Mountain range

Convergent Evolution

• The process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Divergent Evolution(adaptive radiation)

• The process by which related species evolve different traits.

Gradualism

Evolution occurs slowly but steadily.