2.2 Evolution Overview

What is evolution?

Simply, evolution is change over time. More specifically, evolution has occurred when there are genetic changes from one generation to the next in a population of organisms. Sometimes, it is possible to observe evolutionary change: for example, we can detect when a population of gonorrhea bacteria become resistant to a commonly prescribed antibiotic—the antibiotic is no longer effective against gonorrhea. However, some evolutionary changes are too subtle to be detected over the human lifespan.

Is evolution a fact or a theory?

Evolution is both a fact and a theory. When a change in a population can be observed, the observed change is evolution, and it is a fact. However, the mechanism by which the change occurred (such as gonorrhea’s increased resistance to an antibiotic) is open to scientific scrutiny. We can hypothesize that gonorrhea became resistant through one of a few different evolutionary mechanisms, and we can then test appropriate predictions. In over 150 years of exploration, the evolutionary mechanisms discussed below have done an excellent job meeting predictions and explaining how life forms change. In fact, the evidence in support of these evolutionary mechanisms is so overwhelming, we can consider evolution among the most robust of scientific theories.

  Consider the following questions

  • What’s an example of an observable evolutionary change?
  • Define evolution.
  • Why is a non-functioning version of the CCR5 protein potentially advantageous?



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The Evolution and Biology of Sex Copyright © 2020 by Sehoya Cotner and Deena Wassenberg is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.