Chapter 19 Homologous and Analogous Structures. Need to Know The difference between homologous and analogous structures and how this relates to evolution.

Chapter 19Homologous and Analogous

Structures

Need to Know

• The difference between homologous and analogous structures and how this relates to evolution.

• Convergent evolution

Concept 19.3: Evolution is supported by an overwhelming amount of scientific evidence

• New discoveries continue to fill the gaps identified by Darwin in The Origin of Species

• There are four types of data that document the pattern of evolution

– Direct observations– Homology– The fossil record– Biogeography

Homology

• Evolution is a process of descent with modification.

• Homology is similarity resulting from common ancestry.

Example of homology

Example of homology

Video clip

• Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor.

Example of homologous structures

Humerus

Carpals

Radius

Human

Ulna

Metacarpals

Phalanges

Whale Cat Bat

Human embryo Chick embryo (LM)

Pharyngealarches

Post-analtail

Example of homologous structures

• Vestigial structures are remnants of features that served important functions in the organism’s ancestors.

• Vestigial Structure example

• Vestigial Structure example

Example of Convergent Evolution

The wings are analogous.

Shark (Chondrichthyes) Dolphin (mammal)

Example of Convergent Evolution

The fins and streamlined shape are analogous.

Example of Convergent Evolution

AUSTRALIA

NORTHAMERICASugar

glider

Flyingsquirrel

The side flaps of skin are analogous.