There is a second body of evidence that strongly supports the hypothesis that different species have common ancestors.

Imperfect Adaptation

   Paley thought that the exquisite fit of organisms to their environments can be explained only by the hypothesis of intelligent design.

   But today, biologists tell us that organisms are not perfectly suited to their environments. Adaptation is often imperfect, it is good enough so that the species avoids extinction—at least in the short term.

   For example, the panda bear’s thumb is not really an opposable digit—only a spur of bone that sticks out from the panda’s wrist. Considering that the panda depends for its survival on its ability to strip bamboo with its paw and “thumb,” it would have been no great challenge for a skillful designer to design a real thumb for the panda to use.

   But the hypothesis that pandas are closely related to carnivorous bears enables us to understand why pandas have such an awkward contrivance attached to their wrists. The panda’s “thumb” is best understood as the modification of a structure possessed by its ancestors.

   In sum, the panda’s thumb is puzzling if you adopt the hypothesis that God made each organism perfectly adapted to its environment. On the other hand, the hypothesis that pandas are descended from carnivorous bears makes it unsurprising that they have the types of “thumbs” that they do.

   Again, according to the >>> Surprise Principle, the descent-from-bears hypothesis is more plausible.