3.2 Relationship Between Natural Selection and Evolution

For this blog post, we are going to be thinking about natural selection and how it relates (or doesn't!) to evolutionary changes in a species or population. Natural selection allows individuals to survive and reproduce because they have favorable traits that allow their survival. Now, this will mostly allow survival of the favorable individuals, but it won't necessarily make the population evolve. There will still be diversity in the population. Not every species will physically change just so they survive better, some will just have a higher chance of survival. Evolution can occur due to natural selection, but it won't always.  I found a great article explaining this concept. Fisher states, 

"under the idealized conditions of a constant environment, natural selection increases the growth rate of a population, but that, in practice, environmental deterioration owing to physical and biotic changes, including increased population density, has the opposite effect, such that the intrinsic rate of increase fluctuates around zero. Thus, although natural selection often determines which individuals survive and reproduce, the actual number of individuals that survive is generally determined by one or more external limiting factors, such as food, space or predation."

We can see from this extracted quote that natural selection drives evolution. But, the ultimate source of evolution within a species, as stated above, is the food, space, predators, etc. Natural selection can allow organisms to be better suited to conquer these factors, but ultimately if they can survive these limiting factors is what allows evolution to occur.

There are other factors that can influence evolution, such as genetic drift and founder effects. These can select in the absence of natural selection. Genetic drift can actually counter natural selection by the disappearance of a gene (which could've been favorable in their environment). 

Fisher, R. (n.d.). The genetical theory of natural selection. Retrieved February 14, 2021, from https://books.google.com/books?hl=en&lr=&id=WPfvAgAAQBAJ&oi=fnd&pg=PA1&ots=onzPJy20vl&sig=iAqIhwrp5dBiHr6Z3D1OGoaz9oI#v=onepage&q&f=false

Saccheri, I., & Hanski, I. (2006, April 18). Natural selection and population dynamics. Retrieved February 14, 2021, from https://www.sciencedirect.com/science/article/pii/S0169534706001054?casa_token=QM8nl6_RBQ8AAAAA:Ul81GdfA0r0AaL25IfrI0kf0NzBnFa64xDBAHkRlEdDdyuORjUvUmrEMnzucjtB9fzi5GUk9u6Y