The Evolution of Evolution 115of their solutions resembles the wing of a pterodactyl (which is supported only by the bones
of the fourth finger), let alone the completely different structure of the wings of an insect. The
flippers of a whale may perform the same function as the paddles of a marine reptile or the
fins of a fish, but all three structures with a common function have completely different bony
structures. These different types of wings and flippers found in unrelated organisms are
analogous organs that perform the same function but have a fundamentally different struc-
ture. The fact is that organ systems are jury-rigged with whatever bones the animal inherited
from its ancestors and not built from scratch in the optimal shape for its current use. This
only makes sense if life had evolved to use what anatomy is already available.
FIGURE 4.8. The evidence of homology. All vertebrate forelimbs are constructed on the same basic plan with
the same building blocks, even though they perform vastly different functions. The basic vertebrate forelimb
has been modified into flippers in whales, a wing in bats, and a one-fingered running hand in horses, yet the
basic bony structure remains the same. (Drawing by Carl Buell)
Sarcopterygian fishFossil amphibian
FrogLizard ManHorseCatWhaleBatBird