Final answer:
In the context of exaptation, the human middle ear bones derived from ancestral gill arch tissue is an example of a trait that has been repurposed for a different function than what it was originally selected for in evolution.
Step-by-step explanation:
An example of exaptation is provided by option D: Human middle ear bones are derived from ancestral gill arch tissue. Exaptation refers to a trait that has been co-opted for a use other than the one for which natural selection has built it, over evolutionary history. The human middle ear bones, which are crucial for our hearing, were not originally designed for this purpose. Instead, they evolved from structures called the gill arches in fish. Therefore, over time, these structures have been exapted for a new function - hearing in humans.
Options A, B, and C are not examples of exaptation. Option A (Wings of bats and wings of birds are homologous) illustrates homologous structures, which mean they share a common evolutionary ancestry, not an exapted one. Option B (Mutation rates can increase at higher temperatures) is related to environmental effects on genetic mutation rates, not exaptation. Option C (Wings are longer in some birds than others) simply describes variation within a species and does not address exaptation.