Biology Reference
In-Depth Information
Fig. 4.13
The argument here is that a human designer who was trying to make the best
possible wing and the best possible leg would have no need to ensure that the
basic components of these two structures were the same. If he or she did, this
would be a serious limitation on their attempt to produce the best design. Evolution
by natural selection on the other hand, has no knowledge of the best design - it
simply selects from whatever is available at the time for anything that enhances sur-
vival and reproduction in the current environment. Thus the basic structures inside
tetrapod forelimbs are similar because they are related by descent, as predicted by
evolutionary theory, not because they represent the best design.
Anatomical similarities can also be observed during the development of some
animals which differ greatly in their adult forms. Such differences reflect evolu-
tionary changes in the later developmental processes that produce the adult forms,
while the developmental processes that produce the immature forms are more sim-
ilar because they are evolutionarily related. Figure 4.14 shows that the larval stages
of three types of invertebrate are more similar to one another than are the adult
forms.
Religious people who dislike the idea of natural selection sometimes argue that
the similarities between forelimbs illustrated in Fig. 4.13 might reflect the whim of
a supernatural creator. The problem with this type of argument is that it can be used
to explain whatever type of structures are found inside these forelimbs, so it has
no predictive power. The creator might even prefer to create forelimbs that are not
