What is natural selection?

Did you know that evolution and natural selection are not the same thing? Evolution is an observation—humans have observed that populations of organisms can change in as little as a single generation. Probably the most obvious example of this is in domesticated animals selected for a useful characteristic, like cows selected for increased milk production.

But explaining how evolution occurs is another thing, which is where the Theory of Evolution comes in.

The Theory of Evolution is a scientific explanation for what drives evolution. And one of the most important discoveries about what drives evolution is natural selection.

Centuries ago, people noticed that evolution took place and proposed ideas for the mechanism driving it. But, none of the previous ideas stood up to scientific testing.

Then, in 1831, Charles Darwin began his journey around the world on the HMS Beagle and began to notice patterns. Years later, he published a complete description of what he had observed over a lifetime of scientific observation.

The noted difference in survival was what Darwin called natural selection. Nature – the environment and other organisms – selects which organisms survive. Later, the term “survival of the fittest” came to be used interchangably with “natural selection.”

Darwin realized that given enough time this process of natural selection would cause populations of organisms to become very different from their ancestors—the process we call evolution.

One of the primary barriers to understanding the power of natural selection is our own difficulty in comprehending the time spans involved. Because recorded human history is very short with respect to the geological time scale that evolution occurs in, it can be difficult for us to conceptualize natural selection in action. Since the time that life first formed, billions of years have passed. Untold numbers of generations of organisms have lived, reproduced and died. The earth’s atmosphere has changed from supporting only organisms that found oxygen toxic to supporting organisms that require oxygen. Landmasses have formed, split, clashed, and moved all over the earth’s surface. Climates have changed drastically, many times. Rainforests have become deserts, and deserts have become oceans. Mountain ranges have been formed and then worn away to nothing. Islands have formed and submerged. Rivers have formed and run dry. Water has slowly etched canyons and caverns into the earth’s rock. Catastrophes, such as volcanic eruptions and meteorite collisions, have wiped the slate clean multiple times. Extreme weather has pummeled the earth’s surface. For billions of years. Try to imagine what sort of changes any one lineage of organisms has undergone since life first formed. That’s a lot to try to comprehend!

This is where we can make good use of human experimentation with evolution, better known as artificial selection. “Artificial” refers to the fact that humans, rather than nature, are guiding which individuals are selected and allowed to reproduce.

Artificial selection is natural selection put into fast-forward; as when humans do to develop a new breed. This process is called artificial selection.

From the organism’s point of view, artificial and natural selection are the same. Selection pressures, whether “natural” or “artificial,” have the same effect: they prune “negative” traits from a population and enforce “positive” traits. In either case, the adaptations are already present in the population and selection acts as a sieve.

We now understand many of the ways evolution has occurred, and we have found that sometimes evolution occurs by means other than natural selection (e.g., genetic drift). Nevertheless we can see that evolution has occurred, and that these processes still occur—evolution is happening right now.