A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because _____.
a. natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time
b. in many cases, phenotype is determined by genotype and the environment
c. though we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design
d. natural selection is generally limited to modifying structures that were present in previous generations and in previous species
Answer: D