Does evolution only give rise to traits that confer fitness? In other words, does the existence of a trait imply it's conferring of fitness? If not, what are some counter examples?
Answer
Rephrasing the question
Does evolution only give rise to traits that confer fitness?
The phrasing is actually a little nonsensical, but it is easy to understand what you mean. The reason is that "fitness" is not a characteristic of individuals but a measure (a variable if you wish) of a characteristic. Imagine you are talking about Shaquille O'Neal and you say "He is height!" instead of "He is tall!". Allow me to rephrase the question correctly. Note that because "high fitness" is a statement relative to the fitness of the others (just like being tall is relative to the average height), I highlighted in my rephrasing of the question this relativity.
Does evolution only give rise to trait variants that are associated with higher fitness than other variants?
Short answer
No!
Examples
Very simple examples include all the genetic diseases.
Reasons
In short, evolution is much more than natural selection. All of the following are reasons for why there are low fitness variants in nature.
- genetic drift (incl. bottleneck or founder effect),
- spatial variation in the environment and gene flow (hence migration load)
- changing environment (incl. the biotic environment and the social environment) and non-equilibrium conditions in general
- local peaks in fitness (and the concept of pseudo-species; fitness landscape)
- trade-offs
- genomic conflicts
and many others...
For more information on the "why" part of the question, you should start with an intro course to evolutionary biology such as Understanding Evolution by UC Berkeley for example.
No comments:
Post a Comment