Scientists in the United States, Europe, and Africa have now suggested that the hippopotamus is a relative of the whale. Earlier studies placed the hippo as a close relative of wild pigs, but recent studies have discovered
stronger evidence for the connection to whales. This information suggests that
A) scientific explanations are tentative and subject to change
B) genetic engineering was involved in the earlier theories
C) structural evidence is the best evolutionary factor to consider
D) natural selection does not occur in hippopotamuses