A Brief Explanation of Evolution
Tuesday, January 12th, 2010The very wording of most things we’re exposed to on the matter of evolution causes people to frame the process in entirely the wrong way. Too often it’s expressed as being something goal driven, motivated somehow. Bear in mind that this is a simple explanation, and it’s been a long time since I was actively involved with science, so always do your own fact checking. Ok, onward.
For instance, something like- “Human brains evolved to cope with complicated language”
Or- “Kissing evolved to spread germs”
These things are said with authority, and go a long way towards shaping the public’s understanding, yet are completely backwards. Our language grew out of having complex brains, the brains themselves having been built up via selective pressures favoring individuals expressing complex cognition. Individuals that kissed, that had the urge to kiss, didn’t suffer fetus harming pregnancies, which is a pretty quick way to weed out other behaviors.
Nothing evolves to do anything. It’s just stuff that happens that is sometimes beneficial, sometimes detrimental, and most often totally neutral.
Here’s the basics.
Let’s skip how the banging together of chemicals gave rise to the initial organisms on the planet. They were really interesting, and swapped DNA like college kids, but I’m not getting into it.
So. Take a given organism and watch it over time. Variety arises in the genomes of the individuals as they reproduce, primarily through small mutations. If the species reproduces sexually that greatly enhances the variety of the genome, thanks both to drawing from two separate genomes and the DNA juggling done during gamete formation.
Now we get to selective pressure. Something happens that changes the environment in some way. This could be weather, food supply, a species foreign to the area, a dude in coveralls sterilizing all the pigs with long tails, or whatever. The point is that Something Has Changed.
Now our species is challenged, or even dying in droves. Some of them have some trait (or cluster of traits) that previously were neutral, but are now allowing these individuals to survive to one degree or another in this changed environment. This doesn’t always happen, hence extinction. There is no choice, there is no drive, there is simply individuals that live and breed or don’t.
Within our group of survivors there may be several variations on the trait(s) enabling survival, or even completely disparate mechanisms. Typically one will prove more able and overtake the others, though sometimes this just signals a point of divergence as one group of offspring meander off. Like the various primates, or weasels and otters.
Now, it’s important to note here, that this modified species isn’t “better” in any way, it’s just that these are the descendants of individuals lucky enough to have some trait that allowed them to live through this change. There is this commonly held fallacy that evolution is some progression towards a higher or more perfect state. It is no such thing. There is no “next step”. There’s just success or failure, in a biological sense, and it’s entirely dependent on the environmental context. Only through the incredibly hazy view of hindsight does it look like anything else.
Let’s take a real life example. We have a culture of streptococcus, aka strep, aka a bacteria you don’t want. There they are, reproducing away. Now we introduce some penicillin to the media, but not at a high enough concentration to kill the bacteria outright. Some individuals in the culture may die, because they were either carrying a trait that made them sensitive to the antibiotic or were otherwise weakened, while others will slow way down as they process the lethal agent, and still others may have a trait that allows them to perform more or less normally in this environment. A little time passes, and the most resistant individuals will tend to produce the most offspring, because they aren’t busy dying. Now we up the concentration of penicillin. Fewer members die, the next generation will tend to have a high concentration of the most effective coping mechanisms. Repeat this process until you have strep that cannot be killed by any amount of penicillin. Enjoy.
The strep culture didn’t suddenly go “We’re under attack! Hurry, mutate! Fight back!”, it’s just mechanical principles at work. If your culture was totally lacking in traits to survive penicillin type attacks then it wouldn’t go anywhere, just like wishing you could fly, or falling from an airplane, won’t grow wings on you or your children.
This variety of strep isn’t even necessarily better in any objective way from the regular strain. It has extra proteins to code, which eats up resources that would normally go for normal life functions, and may even have other problems.
What kind of problems? Well, let’s look at another real life example. Malaria is a parasite that grows in blood cells (at one stage anyway), interfering with their functions and eventually causing them to burst. Very attractive. A group of humans had the good fortune of getting a gene that causes an infected cell to essentially implode when infected, stopping the infection there. This doesn’t grant total immunity, but it does generally mean the individual lives on and thus procreates.
Sounds good, right? Well. There’s a catch. Two catches, actually. If you have two copies of this gene you have sickle cell anemia. Even just having one copy can cause your blood to start freaking out under certain circumstances.
Now, here’s the thing, even if a trait has negative consequences, it will continue to be present in a species so long as the individuals live long enough, and are healthy enough, to spawn kids and raise them to a point where they can care for themselves, and if they happen to be the type of critter to raise strange children then it doesn’t matter if the individual even lives that long.
It’s like smoothing a branch by forcing it through a hole in a rock over and over.
