Can One Work Without the Other?
I honestly wasn't sure how to answer these questions. I had to wrack my brain and go surfing through Google's resources to try and see actual, verifiable examples of natural selection working without leading to evolution. Natural selection is a mechanism that leads to evolution, but I don't think it's the only one. Genetic mutations are also a key part of the change.
In the first chapter of the book, when it talks about evolution and what it is, one of the passages on page 4 reads: Natural selection is one process that can cause evolutionary change, but natural selection can occur without producing evolutionary change. Conversely, processes other than natural selection can lead to evolution.
It follows after with an example: Natural selection within populations refers to the situation in which individuals with one variant of a trait (say, blue eyes) tend to leave more offspring that are healthy and fertile in the next generation than do individuals with an alternative variant of the trait.
It goes on with how it can impact it by making that organism more desirable, increase of lifespan, or even increased offspring production. The catch to all of this, however, is that the differences among the individuals in the population are not genetically based. That is what can lead to natural selection without evolution. If variation in a population isn't genetically based, then it doesn't lead to evolution.
If we flip it and question if evolution can happen without natural selection, then it can happen through these means: mutation, genetic drift, and immigration of individuals with different genetic makeup. As the book says, "Natural selection can cause adaptive evolutionary change, but not all evolution is adaptive."
I agree with both sides of your post how natural selection can cause adaptive evolutionary change, but not all evolution is adaptive. I also went along with this thought process on my blog post. And as we learned in the R exercise, we did find that the differences among the individuals in the population are not genetically based. I enjoyed the memes!
ReplyDeleteI was wracking my brain over these questions as well. I think that even if it a trait was genetically based, it doesn't necessarily mean that it will lead to evolution. It has to be heritable for evolution to occur. The R exercise we did with the fish showed that the body size trait was not heritable. There would still have to be genetic factors that determine the body size of the fish, but these genetic factors were not passed on to the offspring. So it has to be not only genetically based, but heritable as well.
ReplyDeleteI like that you talk about factors other than selection that can cause evolution like mutation, genetic drift, etc. I have been pondering your last sentence; do you think natural selection can cause evolution that is not adaptive?