Only Populations Can Evolve

Individual adaptations denote mutations, not a species' evolution

Grazing zebras
Peter Maas

One common misconception about evolution is the idea that individuals can evolve, but they can only accumulate adaptations that help them survive in an environment. While it is possible for these individuals in a species to mutate and have changed made to their DNA, evolution is a term specifically defined by the change in DNA of the majority of a population.

In other words, mutations or adaptations do not equal evolution.

There are no species alive today that have individuals that live long enough to see all of the evolution happen to its species—a new species may diverge from an existing species’ lineage, but this was a build up of new traits over a long period of time and did not happen instantaneously.

So if individuals cannot evolve on their own, how then does evolution occur? Populations evolve through a process known as natural selection which allows individuals with beneficial traits for survival to breeding with other individuals who share those traits, eventually leading to offspring who only exhibit those superior traits.

Understanding Populations, Evolution, and Natural Selection

In order to understand why individual mutations and adaptations are not in and of themselves evolutionary, it's important to first understand the core concepts behind evolution and population studies.  

Evolution is defined as a change in the inheritable characteristics of a population of several successive generations while a population is defined as a group of individuals within a single species that live in the same area and can interbreed.

Populations of individuals in the same species have a collective gene pool in which all future offspring will draw their genes from, which allows natural selection to work on the population and determine which individuals are more “fit” for their environments.

The aim is to increase those favorable traits in the gene pool while weeding out the ones that not favorable; natural selection cannot work on a single individual because there are not competing traits in the individual to choose between.

Therefore, only populations can evolve using the mechanism of natural selection.

Individual Adaptations as a Catalyst for Evolution

This isn't to say that these individual adaptations do not play a role in the process of evolution within a population—in fact, mutations that benefit certain individuals may result in that individual being more desirable for mating, increasing the likelihood of that particular beneficial genetic trait in the collective gene pool of the population.

Over the course of several generations, this original mutation could affect the entire population, eventually resulting in offspring only being born with this beneficial adaptation that one individual in the population had out of some fluke of the animal's conception and birth.

For instance, if a new city was built on the edge of the natural habitat of monkeys that had never been exposed to human life and one individual in that population of monkeys were to mutate to be less afraid of human interaction and could therefore interact with the human population and perhaps get some free food, that monkey would become more desirable as a mate and would pass those docile genes onto its offspring.

Eventually, the offspring of that monkey and that monkey's offspring would overwhelm the population of formerly feral monkeys, creating a new population that had evolved to be more docile and trusting of their new human neighbors.

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Scoville, Heather. "Only Populations Can Evolve." ThoughtCo, Feb. 6, 2018, thoughtco.com/only-populations-can-evolve-1224608. Scoville, Heather. (2018, February 6). Only Populations Can Evolve. Retrieved from https://www.thoughtco.com/only-populations-can-evolve-1224608 Scoville, Heather. "Only Populations Can Evolve." ThoughtCo. https://www.thoughtco.com/only-populations-can-evolve-1224608 (accessed May 24, 2018).