A) New mutations are usually maladaptive.
B) Environments change slowly.
C) Gene flow keeps individuals similar to each other.
D) Natural selection is a powerful process.

A) experience different mutations.
B) living in the same location experience different selection pressures.
C) form fertile hybrids.
D) are physically separated from each other.

A) cannot be maintained without good geographical separation.
B) are very flexible, so closely related species are easily confused.
C) are maintained by genetic drift.
D) are maintained by selection, even if they overlap in geography.