What is Natural Selection?

To start at the beginning and lay the foundation for future posts, I am discussing a term familiar to many people, but important to grasp in all of its nuance (I am assuming a very basic understanding of evolution here). So then, what is Natural Selection?

Natural selection is a way in which evolution can happen, with evolution being the change in life forms (or organisms) over time. Darwin wasn’t the first person to suspect that the life that surrounds us (and ourselves) had changed in history, but is contribution was to suggest a mechanism through which it happens: Natural Selection.

What enabled Darwin to figure out how evolution can work was a change in perspective. Instead of thinking about individual organisms, like his predecessors, he envisioned change at the level of groups of organisms. To clarify, as opposed to looking at change during the life time of one organism, he looked at the change in the composition of groups of such organisms (populations) over successive generations. This “simple” shift in thinking led him to one of the greatest and simplest ideas in biology.

Resources are finite on our planet. There is only so much sunlight for plants to share, so much grass to eat, so many prey to consume… Darwin realised this meant that whichever organisms were better at obtaining said resources would survive longer and reproduce more. Those individuals would then pass on the traits that enabled them to do so to their offspring, and over time the composition of the population would shift towards organisms possessing those traits.

Note that this excludes changes that occur during the organism’s lifetime. Evolution by Natural Selection is therefore simply a shift in trait frequency in a population over time. It’s important to note that Natural Selection does not really exist in a sense, it is not a force that acts on species to shape them. To me, this is at once confusing and wonderful: rather, Natural Selection is a property that emerges from each individual’s “struggle for existence”, each individual’s fight to survive and reproduce.

Over time, this “culling” of bad traits and “selection” of beneficial traits will lead to groups of organisms being more and more in tune with their environments, better at exploiting it. This is adaptation by Natural Selection.

Natural Selection implies three properties about the population we are looking at:

That there is variation in the population. Without variation, there can be no change in the frequency of traits.

That this variation affects survival and/ or reproduction.

That this variation is heritable. If the character is acquired throughout an organism’s lifetime but not passed on to future generations, then if there is change in the trait’s frequency it will have nothing to do with Natural Selection.

The simplicity yet complexity of the result of this process is amazing. However, we must delve in much deeper to understand the complexity of life that surrounds us. This process underpins many things that happen in evolution, but things get tricky. I’ll get to some of that in future discussions!

Bye for now,

Juliette

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