“When it was introduced in the 1940s, penicillin was a miracle drug, especially effective at curing infections caused by the bacterium Staphylococcus aureus (“staph”). In 1941, the drug could wipe out every strain of staph in the world. Now, seventy years later, more than 95% of staph strains are resistant to penicillin.” — Dr. Jerry Coyne, Why Evolution is True, p. 131
In Why Evolution is True, Dr. Coyne used this example in the chapter entitled, “The Engine of Evolution.” The engine he’s referring to is none other than natural selection, and this little insight regarding the adaptability (evolution) of Staphylococcus aureus is excellent evidence for the theory of evolution by natural selection. It’s my go to “proof,” if you will, when someone asks me to provide proof of evolution because (a) it’s simple and easy to understand, (b) it definitively shows that an organism can adapt to a new environment, in this case a human body injected with penicillin, (c) it doesn’t require any talk regarding fossils or the fossil record (which is probably the best evidence for evolution, but it’s very difficult to explain to someone who wants to “see” evolution if you don’t have fossils on hand!), and (d) bacteria are excellent for ‘showing’ evolution in action because they reproduce quickly meaning that they can potentially evolve much more quickly than, say, a dog or a dolphin. Let’s expand on point (d) for further clarification:
Bacteria can reproduce in as quickly as 20 minutes, so if you leave some bacteria alone for 24 hours, they will have gone through 72 generations. 72 generations in regard to a human generation (~25 years) is equivalent to ~1800 years. So, you can see that you can get a good amount of change in a very short amount of time. In regards to the example, the bacteria had 70 years to evolve. That’s equivalent to, if I did my math correctly…, ~74,000 human generations, which is about 1.8 million years! And that’s just for a single bacterium! To put that in perspective, our species, Homo sapiens, has only been around for about 200,000 years, and Homo erectus, a long extinct hominin of our genus, would have still been walking around that many years ago! And, 1.8 million years just so happens to coincide with the approximate distance you’d have to travel into the past to see the first hominids make their way out of Africa!
Now, I’d like to point out a statement made by a famous biologist and geneticist and Nobel Prize winner, Jacques Monod:
“A curious aspect of the theory of evolution is that everybody thinks he understands it.”
I added that quote for an important reason, and, now, I’d like those who have little to no background in evolutionary theory to stop for a moment, take a breath, and forget everything you think you know about evolution, notable exceptions being what I wrote in the first two paragraphs! I say this because many people believe they know exactly what the phrase “evolution by natural selection” means. You may have heard people talk about it, or maybe it was being discussed on the news. For many, the words “random” and “chance” (or “random chance”) come to mind. Also, the phrase, “survival of the fittest,” may pop into your head along with the notion that natural selection is some type of force (dynamism is the word I hear too much of in this respect) pushing evolution to some certain goal. Forget all of these things. None of these things are true, although “survival of the fittest” is technically close to the truth, but not a truth in and of itself. Now, let us “define” natural selection:
The Tangled Bank, which is a ‘textbook’ intended for the general reader who may not be fluent in the “language of biology,” defines natural selection as, “The process by which individuals better adapted for their way of life in their environment preferentially survive to leave more offspring with their traits to future generations.” (p. 356)
This definition is true, but it’s not as descriptive as I’d like. It’s difficult to truly “define” natural selection, as it were, in one sentence as it’s a process, and processes require descriptions. It’s like trying to explain the process of a volcanic eruption in a single sentence. You can try, but it’s going to be one hell of a run-on sentence! I prefer, then, the description provided, once again, by Dr. Coyne in Why Evolution is True:
“The idea of natural selection is not hard to grasp. If individuals within a species differ genetically from one another, and some of those differences affect an individual’s ability to survive and reproduce in its environment, then in the next generation the “good” genes that lead to higher survival and reproduction will have relatively more copies than the “not so good” genes. Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population while deleterious ones are weeded out. Ultimately, this process produces organisms that are well adapted to their habitats and way of life.” (Why Evolution is True*, p.11)
To show you how simple of a process this is, let’s take a look at a hypothetical example in nature. (I say “hypothetical,” but it’s entirely plausible that something similar to this has or could have occurred).
Picture in your mind a stick insect. (If you’re having trouble doing so, click here, then come right back). Now, imagine that this stick insect carries a gene mutation which makes it somewhat more “stick like” than another similar stick insect, i.e., your imagined stick insect is better camouflaged than another stick insect. It follows, then, that this stick insect which is somewhat better camouflaged, that is, better adapted to its environment, will have a better chance to survive and reproduce than the other stick insect as it’s less likely to be seen and thereby eaten by a predator such as a bird. When this stick insect reproduces, it’s likely to pass on this “good” mutated gene to its offspring. These offspring will then be better camouflaged (adapted) and therefore more likely to survive and reproduce than the other stick insects which don’t carry this gene. They’ll produce more offspring, who will produce more offspring, and so on and so forth. Over a long period of time, the stick insects with the original gene mutation will come to outnumber those without it due to environmental pressures, namely predation. These stick insects are then said to have been “naturally selected” as they are more adapted to their environment (they are “fitter”) than their predecessors making them more likely to survive and reproduce. So, essentially, the phrase should be “survival of the ‘fitter’,” not “survival of the fittest.”
Now, the reader may have noticed that I’ve yet to define or describe evolution itself. I realize this, and I also realize that it’s quite unorthodox to begin a series on evolution by describing natural selection. But, it’s been my experience that most of the controversy and confusion surrounding evolution regards natural selection. As this blog progresses, we will go more in depth into evolutionary theory, but I hope this post has dispelled any misconceptions you may (or may not) have had regarding natural selection, and I sincerely hope that you’ve learned a thing or two that you can go and share with others! I leave you, then, with the famous final paragraph of Darwin’s seminal work, The Origin of Species, as one cannot write about natural selection without mentioning Darwin at least once!
“It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.”
Thanks for reading!
P.S. Please feel free to comment below if you have any comments, questions, or criticism, and I will be sure to respond as soon as I can. Or, you can contact me on Twitter @NonrandomEvo, or use the “Contact Me” link at the top right corner of this page to send me an email!
*I generally do not like to use the same source more than once, but it just so happens that Coyne’s description of natural selection is the best (and simplest to understand) description I’ve come across (so far). I opine that many sources, such as the average internet user’s favorite source, Wikipedia, use definitions and/or descriptions of natural selection that can be confusing or difficult for the average person to understand.
Why Evolution is True, Dr. Jerry A. Coyne
The Blind Watchmaker, Dr. Richard Dawkins
The Tangled Bank: An Introduction to Evolution, Carl Zimmer