Chapter 17, Problem 11STP

Summary Introduction

To explain:

The difference between homologous structures and analogous structures in terms of their evolution.

Introduction:

The evidence for evolution is more convincing when it is supported by many pieces of evidence. Darwin’s theory of natural selection is part of the larger theory of evolution which states that all organisms on Earth have descended from a common ancestor. Comparative anatomy also provides some evidence for evolution.

Answer to Problem 11STP

Homologous structures	Analogous structures
They are similar in anatomy	They are not similar in anatomy
They are inherited from common ancestor	They are not inherited from common ancestor
They are dissimilar in function	They are similar in function
They are developed in related species	They are developed in unrelated species
They suggest evolutionary relationships among species	They do not suggest evolutionary relationships among species
They suggest that anatomically similar structures can evolve independently in different environments	They suggest that functionally similar structures can evolve independently in similar environments
Example: Bird wings and reptile limbs are homologous structures	Wing of an eagle and wing of a beetle are analogous structures

Explanation of Solution

Anatomically similar structures inherited from common ancestor are called homologous structures. Bird wings and reptile limbs are homologous structures as both are used for movement and are similar in shape and construction. The forelimbs of vertebrates are also homologous structures as they all have similar bones but adapted for different uses. This suggests that they were inherited from a common ancestor.

Functionally similar structures but not inherited from common ancestor are called analogous structures. They are superficially similar in construction. Wing of an eagle and wing of a beetle have the same function- to fly- but they are constructed in different ways from different parts. Analogous structures do not indicate close evolutionary relationships but they suggest that functionally similar structures can evolve independently in similar environments.