Concept 24.3

Q1: How can the Darwinian concept of descent with modification explain the evolution of such complex structures as the vertebrate eye or heart?

A1: Such complex structures do not evolve all at once, but in increments, with natural selection selecting for adaptive variants of the earlier versions.

Q2: Explain why the concept of exaptation does not mean that a structure evolves in anticipation of some future environmental change.

A2: Although an exaption is co-opted for new or additional functions in a new environment, it existed in the first place because it worked as an adaptation to the original environment.

Q3: How can heterochrony cause the evolution of different body forms?

A3: The timing of different development pathways in organisms can change in different ways (heterochrony). This can result in differential growth patterns, such as those producing different patterns of webbing in salamander feet.