Not everything is an adaptation
Although living things sport some amazing adaptations,
many characteristics of species are not adaptations at all.
It's tempting to look for adaptative explanations for everything,
from the shape of a flower petal, to the way your dog turns in a
circle before it lies down to sleep, to your neighbor's strawberry blond hair.
We could make up an adaptive explanation, but there are other explanations to consider:
- The result of history. Why does the base sequence GGC code for the amino acid glycine in a protein, as opposed to some other amino acid? Because that's
the way it happened to start out and that's the way we inherited it from
our common ancestor. There is nothing special about the relationship
between GGC and glycine. It's just a historical accident that stuck
Just a by-product. Why is blood red? It's a by-product
of the chemistry of blood, which causes it to reflect red light.
The chemistry of blood may be an adaptation, but blood's redness is not itself
- An outdated adaptation. It might be an adaptation for
a past environment and not the current one. For example, scientists have
hypothesized that the large, hard-shelled fruit of the calabash
tree is actually an adaptation for seed distribution by large mammals
such as the gomphothere. But these early relatives of elephants
went extinct over 10,000 years ago! If the hypothesis is correct,
these fruit characteristics can no longer be considered adaptations
for seed distribution.
|An artist's representation of a gomphothere (extinct).
||A modern-day calabash fruit.
- The result of genetic drift. Some biologists can get quite
passionate about how much genetic variation is adaptive and is maintained by natural selection
and how much is neutral and is maintained by genetic drift.