Understanding Evolution: What is Natural Selection?
“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 c
ould
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 discourse regarding
fossils or the fossil record (which is probably the best evidence for
evolution, but it’s very difficult to explain fossil evidence 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
faster than, say, a dog or a dolphin.
Let’s expand on point (d) for further clarification:
Bacteria can reproduce in as little as 20 minutes, so if you leave some
bacteria alone for 24 hours, they will have gone through 72
generations. 72 generations in regards to a human generation (~25 years)
is equivalent to ~1800 years. So, you can see that, in bacteria, you
can get a good amount of change in a very short amount of time. In
regards to the above example (Staphylococcus aureus and penicillin), the
bacteria had 70 years to evolve and become resistant. That’s equivalent
to, if I did my math correctly… ~74,000 human generations, which would
be about 1.8 million years for us! 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, geneticist and Nobel Prize winner, Jacques Monod:
“A curious aspect of the theory of evolution is that everybody thinks they 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). Forget all of
these things. None of these things are true. “Survival of the fittest”
is technically *close* to the truth, but not a truth in and of itself.
Now, let us “define” (describe) natural selection:
“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. Now, imagine that this stick
insect carries a gene mutation which makes it somewhat more “stick like”
than another similar stick insect. That is to say, your imagined stick
insect is better camouflaged than another stick insect. It follows,
then, that the 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. Ultimately, the
better-camouflaged is 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. 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 being better adapted to their environment, i.e.,
in this example, they are less likely to be eaten by predators and
therefore more likely to survive, allowing them to produce more
offspring. 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. In the future, 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!
- Jake West
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. The original piece can be
viewed in its entirety on my blog: http://nonrandomevolution.wordpress.com/2013/04/24/the-evidence-for-evolution-intro-to-natural-selection/
*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 my
favorite (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.
Sources:
"Why Evolution is True," Dr. Jerry A. Coyne
"The Blind Watchmaker," Dr. Richard Dawkins
Biology 111....
For more reading:
http://evolution.berkeley.edu/evolibrary/home.php
Image Source before editing:
http://thoriumforum.com/nasa-researchers-natural-gas-would-cause-far-more-deaths-nuclear
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