Question

which statement best describes how homologous structures evolve?
similar structures evolve independently in distantly related species that experience similar problems in their habitats.
two species evolve the same structure when the same mutation occurs independently in both species.
different species may evolve different variations on a basic structure inherited from a common ancestor.
members of a species come to resemble each other strongly as extreme structures are eliminated from the species.

Explanation:

Homologous structures are anatomical features in different species that are derived from a common ancestor. They may have different functions but share a similar basic structure. For example, the forelimbs of humans, bats, and whales have different uses (grasping, flying, swimming) but a similar bone - structure inherited from a common vertebrate ancestor.

• The first option describes analogous structures (not homologous) which evolve due to similar environmental pressures in distantly related species.
• The second option is an incorrect explanation for homologous structures. Homologous structures are due to common ancestry, not independent same - mutation events.
• The fourth option is about intraspecies similarity (due to elimination of extreme forms, like in stabilizing selection) and not about homologous structures between different species.

Answer:

Different species may evolve different variations on a basic structure inherited from a common ancestor.