IB Biology Topic A4.1 Evolution and Speciation…

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

Definition

Homologous structures

Homologous structures are anatomical features that share a similar structure and position across different species but serve different functions.

Homologous structures share the same underlying structure but are used for different functions.
That shared plan is evidence of inheritance from a common ancestor, the pattern we call divergent evolution.
Darwin called this shared design unity of type.

Example

A human hand grasps, a bird wing flies, and a whale flipper swims, yet all share the same bone arrangement.

The Pentadactyl Limb Is the Classic Homologous Structure

The pentadactyl limb is the five-digit limb pattern shared by all tetrapods.
Its bones run in the same order from the body outward:

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

Definition

Homologous structures

Homologous structures are anatomical features that share a similar structure and position across different species but serve different functions.

Homologous structures share the same underlying structure but are used for different functions.
That shared plan is evidence of inheritance from a common ancestor, the pattern we call divergent evolution.
Darwin called this shared design unity of type.

Example

A human hand grasps, a bird wing flies, and a whale flipper swims, yet all share the same bone arrangement.

The Pentadactyl Limb Is the Classic Homologous Structure

The pentadactyl limb is the five-digit limb pattern shared by all tetrapods.
Its bones run in the same order from the body outward:

A4.1B Evidence from structures; speciation and reproductive isolation

A4.1B Evidence from structures; speciation and reproductive isolation

Subtopics and learning objectives

A4.1.4 Evidence for evolution from homologous structures

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

The Pentadactyl Limb Is the Classic Homologous Structure

Unlock the rest of this chapter with a free account

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

The Pentadactyl Limb Is the Classic Homologous Structure

Unlock the rest of this chapter with a free account

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

A4.1B Evidence from structures; speciation and reproductive isolation

A4.1B Evidence from structures; speciation and reproductive isolation

Subtopics and learning objectives

A4.1.4 Evidence for evolution from homologous structures

A4.1.5 Convergent evolution as the origin of analogous structures

A4.1.6 Speciation by splitting of pre-existing species

A4.1.7 Roles of reproductive isolation and differential selection in speciation

A4.1.4 Evidence for evolution from homologous structures

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

The Pentadactyl Limb Is the Classic Homologous Structure

Unlock the rest of this chapter with a free account

Same Skeleton, Different Jobs: Homologous Structures Point to a Common Ancestor

The Pentadactyl Limb Is the Classic Homologous Structure

Unlock the rest of this chapter with a free account