Natural Selection

Here is the boring definition:

The process in nature by which only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.

Here is the super short definition:

Survival of the fittest.

Here is the still-rather-short-but-a-bit-more-accurate definition:

Survival and reproduction of the fittest.

The basic idea is that nature is a constant struggle to stay alive and reproduce, and not every organism that is born survives long enough to pass on their genes–only the “best” or the “fittest” are able to, which means that the “best” and “fittest” genes are the only ones to get passed on. So over time, a group of organisms becomes more adapted to its unique environment.

It’s not very helpful to think about Natural Selection in human terms because we don’t have hundreds of kids assuming that only a fraction of them will survive to adulthood. Humans have a different strategy–we have just a few and invest a lot of time and energy into them (note to self: call my mom tonight). We are not the only species with this strategy, but it isn’t as common as the other strategy: have hundreds of kids and hope that 1 or 2 make it.

Think about sea turtles. They lay dozens of eggs on a sandy beach, bury them, and take off. The mother doesn’t get to see them hatch, run for their lives from hungry sea gulls, and grow to adults. She does what she can in the hopes that maybe 1 of those dozens of eggs has a future as a 100 year-old turtle. And just 1 is probably all it will be.

We humans have separated ourselves from nature in many ways, so we forget that survival is a constant struggle, and one that not every creature wins. To survive and have babies that will inherent one’s qualities, a creature must survive it all: disease, injuries, predation, weather, unpredictable food availability, and so on.

Many people misunderstand Natural Selection, thinking that the species can somehow “choose” to adapt to a situation. I think this might stem from the common nature show host saying something like, “and so the gazelle must adapt to its environment or perish!” It really doesn’t work this way. A species can no more choose to adapt than you can choose who your parents are. It’s really based on chance. Natural Selection can only select traits that are already there.

Another example of this misunderstanding: Kevin Costner’s character in Waterworld (did that character even have a name?). He has gills, and the other people are either terrified or intrigued by them, but this implies that he developed gills because humans are living in water now. This makes it seem like there is a cause-effect relationship here: “hmm, now we humans have to deal with water. Let’s make us some gills!” Sadly, this is not the way things work. The odds of a human spontaneously being born with gills are the same whether or not the earth is covered in water. And what are those odds? Well, slim to none. Sorry, Kevin.

You heard it here: a changed environment or some new need does not create new traits. Instead, individuals that are better suited for a new situation will survive and reproduce, and the ones that aren’t suited… well, they don’t survive or they don’t reproduce.

So Natural Selection doesn’t create new traits, it just selects the “best” of what is available. What, then, does create new traits? How do things adapt, changing slowly over time?

The answer, my dear, is variation, diversity, and just a pinch of randomness. Variation is built into every step of the process that we call “life.” Reproduction shuffles genes around, creating different combinations of traits. Random genetic mutations can create new traits, and even certain sequences of DNA can be turned “on” and “off” by a variety of factors.

In summary, you, my friend, are the result of 3.5 billion years of life slowly changing from a single-celled creature to the walking, talking, cell-phone-toting creature that is you. You are alive because not a single one of your ancestors, going back those billions of years, didn’t make it. Every single one of them survived long enough to reproduce, passing their genes on to the next generation. None of your predecessors fell off a cliff or was eaten by a bear (before reproducing, that is). You are a shining beacon of hope in the universe, proving that life can and will prevail! Now go shout it from the rooftops! (But, um, don’t fall off.)