Claim CB902.2:
Creationists recognize that small microevolutionary changes occur, but
small changes do not imply large changes, so the theory of macroevolution
is unjustified.
Response:
- This claim falsely assumes that the conclusion of macroevolution is
based solely on the observation of microevolution. In fact,
microevolution is just one piece of the evidence that demonstrates
evolution as a whole. Other evidence
includes the fossil
record, patterns of similarities and differences between living
species, and genetic comparisons (Darwin 1872; Theobald 2004).
- Small changes do imply large changes under some common circumstances.
If there is some selective pressure for the changes to go in one
direction, the changes will add up. Such a condition can happen, for
example, under a gradual climate change or in evolutionary arms races.
Even if there is no selective pressure at all, the changes will tend to
diverge further and further from the starting point. Small changes
will not lead to large changes only
- if there is stabilizing selection for organisms to remain as they
are, or
- if there is too little time for much to happen, or
- if there are genetic mechanisms limiting change.
Stabilizing selection occurs sometimes but is far from universal. We
know that the earth, and life on it, is very
old. And there is
no hint of a mechanism to limit variation.
Therefore, we
expect large changes based on basic principles.
Links:
Theobald, Douglas, 2004. 29+ Evidences for macroevolution: The
scientific case for common descent.
http://www.talkorigins.org/faqs/comdesc/
References:
- Darwin, C. 1872. (see below)
- Theobald, D. 2004. (see above)
Further Reading:
Darwin, Charles. 1872. The Origin of Species, 1st Edition. London:
Senate. http://www.talkorigins.org/faqs/origin.html
created 2003-7-15