Biology Reference
In-Depth Information
Chapter 4
The Evidence for Evolution
Now I want to turn to the evidence for evolution. If you ask the average person-in-
the-street about this, they will probably mention the fossil record - the remains
of types of organism no longer living on the Earth. But this is incorrect
-
the
fossil record is consistent with both separate creationism and with transformism,
which, you will recall, both propose that species had separate, natural origins
but can become extinct. Darwin did not use the fossil record as one of his main
lines of evidence to support the idea of evolution because he thought that there
were not enough fossils known in his time. He devoted a whole chapter in
On
the Origin of Species
to this problem, stressing the absence of numerous transi-
tional forms between fossil species and species alive today that his theory predicted
should occur. He suggested that this absence could be explained if the fraction
of organisms that end up as fossils is extremely small and dependent on partic-
ular geological events that themselves vary with time. He lists at the end of the
chapter the names of nine eminent scientists that specialised in studying fossils
in his day but who rejected the idea that species had changed over geological
time.
What the fossil record shows is that in the past there were organisms that are
not around today, but some of the fossils discovered since Darwin's time are of
organisms that show features intermediate between those of the major groups of
organism alive today. For example, some fossils are of animals that had feathers
and wings, like birds do today, and teeth and bony tails, like reptiles do today.
Such transitional features are expected if evolutionary theory is correct, but are
not strictly ruled out if either separate creationism or transformism is correct. So,
while the fossil record is consistent with evolution, of itself it does not exclude
other logically possible naturalistic explanations. So what is the evidence for
evolution?
Figure 4.1 lists seven of the main lines of evidence for evolution.
The first line of evidence concerns similarities between organisms that you would
not expect if they had independent origins. These similarities are found at all levels,
from the molecular to the anatomical; I will show you examples from two levels.
These similarities are often referred to as “homologies”, but there is a possible
