I don’t know, Morpheus. What if I told you that cylinders, driveshafts, tires, doors, headlights, and bumpers have nothing to do with automobiles? You’d probably say I didn’t understand the topic at all, or that I was barking mad. And if I made a statement as breathtakingly inane as the one in this meme, you’d be quite right to think so.
This is a common Creationist tactic called “moving the goalposts”. First, Creationists said that evolution never happened. Biologists showed that evolution happens everywhere, all the time. When the evidence became irrefutable, Creationists said fine, organisms can adapt within a created kind, but one species cannot evolve into another one. A fish cannot become an amphibian, for example. Paleontologists showed that organisms have been evolving from one species to the next for billions of years, and continue to do so. Scientists defined terms like natural selection, genetic drift, and speciation to describe exactly how species change over time. This Creationist memer seems to imply that these phenomena exist, but they don’t contribute to the process called evolution. What? If you argue that the very components of evolution have nothing to do with evolution, then you’re simply re-defining evolution in such vague and unattainable terms that nothing would ever qualify as evolution. You’ve moved the goalposts clear into the parking lot.
You don’t get to redefine scientific terms in order to discredit them. If you want to prove that evolution – a scientific concept – isn’t real, then you have to stay within scientific boundaries to do so.
Since we’re going to be talking about evolution a lot over the course of the coming week, I thought it would be helpful to define each of the terms in this meme. I should warn you up front: there’s a lot to talk about. Go ahead and grab another cup of coffee. I’ll wait.
What is evolution?. In simplest terms, evolution is a change in allele frequency within a population over time. Alleles are different flavors of a gene; they give rise to the various traits that make us diverse and wonderful. The word frequency refers to how often these alleles are found within the genes of a population. For scientific purposes, a population is a group of organisms belonging to the same species and living in the same region.
Anything that happens to change how often these genetic traits are found within a population is evolution. On short time scales, evolution causes minor changes within populations, but eventually little changes add up to big changes.
Now wait just a minute, you might be asking. When do we get mutant powers and the ability to breathe underwater? Well, that leads us to the next question…
What isn’t evolution? It’s really important to understand this, because Creationists rely on a (sometimes deliberate) misunderstanding of evolution to form their arguments. Here’s a partial list of things that aren’t evolution:
- A chimpanzee giving birth to a human.
- A chimpanzee turning into a human.
- A chimpanzee learning some human language skills.
- A human sprouting wings.
- Anything you see on X-Men.
- A half-duck half-crocodile.
All of these events (with the exception of the third item) would qualify as miracles, not evolution. A miracle does not have to obey the laws of nature; evolution does.
What is natural selection? Natural selection is the process that drives evolution. There are a few simple principles to remember:
- Resources are limited in any environment, so there will always be competition among members of a population.
- Genetic variation (arising from mutations) causes inheritable differences.
- Some organisms will have advantages over other organisms because of their interited traits. They will be more effective competitors for food, shelter, mates, etc.
- Due to the increased health and vigor afforded them by their inheritance, these organisms will reproduce more often and leave behind more viable offspring. Their advantageous genes will proliferate in future generations, while the offspring of the less well-adapted members of society become marginalized.
And that, my friends, is evolution.
What is a mutation? A mutation is a change in the genes of an organism. Genes code for proteins, which are important for supporting your cells and helping them carry out biological tasks. This code relies on a very precise sequence of bits called bases, organized into the double helix of DNA. When DNA is copied during cell division, the sequence of bases has to be perfectly preserved so that each daughter cell can carry out its functions correctly.
The copying process isn’t always precise. Mistakes can be made, and despite your cells’ best efforts for identify and correct these mistakes before they become permanent, some slip through. They get copied into the next generation of cells, and so on, and so on.
So what happens when a cell’s genes become mutated?
In some cases, nothing. Each human cell contains a lot of DNA that doesn’t seem to code for anything in particular. This DNA may be an evolutionary relic, or it may have some function that is not yet understood. In any case, a mutation occuring in this “junk DNA” doesn’t affect the cell very much at all. Some mutations are harmful to the cell, especially if they prevent the production of a protein that the cell needs to produce energy. Occasionally, though, a chance mutation occurs that is actually beneficial to the organism. These mutations give rise to the traits that make an organism’s offspring better suited to survive and reproduce.
“Good” mutations are very rare, which is why evolution can be such a slow process. But if you have enough organisms in one area competing for survival, this increases selective pressure for beneficial mutations. Remember: mutations are random, but the processes that single them out for proliferation are not.
What is genetic drift? Genetic drift is related to the random nature in which alleles are distributed during reproduction. Remember when I said that we all have two copies of each gene? When your body makes sperm or eggs, each future you gets only one copy of each gene. Half of your gametes (sperm or egg cells) will carry one copy of each gene you have, and half will carry the other copy. The actual traits that show up in your children depend on the combination of half of your genes with half of your mate’s genes. It’s sort of like a genetic lottery.
Imagine that there are only four people on Earth: two men and two women. They are all healthy and of reproductive age. They pair off to mate, and each couple gives birth to two children in due course.
Now each parent carries two copies of the gene that determines earlobe shape, and that gene comes in two varieties: dangly or attached. For the sake of argument, let’s assume that each one of the parents is heterozygous (meaning they carry one attached and one dangly allele). Because of the way that alleles interact, the parents will all have dangly earlobes, but they have the potential to give birth to children with attached earlobes.
When their children are conceived, each child can receive either two dangly alleles, one dangly and one attached allele, or two attached alleles. It’s completely random. In a huge population, you’d expect twenty-five percent of the offspring to get two dangly alleles, fifty percent to get one of each, and twenty-five percent to get two attached alleles. But in very small populations, the laws of probability don’t necessarily apply like you think they should. It’s entirely possible that every single child could receive only dangly alleles, and the attached allele would completely disappear from the population after the parents croak.
Genetic drift becomes less important in large populations, but it can play a huge role in the future evolution of a species if that species is ever reduced to a dangerously low population. Just one more reason to be concerned about the conservation of threatened species. But I digress.
What is gene flow? Gene flow happens when separate populations of an organism are able to exchange genes. If the populations were completely isolated, genetic differences would accumulate over time until they became separate species, no longer able to interbreed even if they were re-introduced to each other. But if genes can move from one place to the other, the separate populations might be prevented from evolving into distinct species.
Imagine bird populations living on opposite sides of a mountain range. Their environments are remarkably different; one lives in a lush, semi-tropical jungle that is constantly nourished by rain; the other lives in an arid rainshadow desert. Faced with very different challenges, they may start to evolve apart – to form distinct species. But if there are mountain passes low enough to allow the birds to mingle, their interbreeding might keep the genomes from diverging enough to form different species. In a way, gene flow can hinder the formation of new species (although it still serves as an agent of evolution because it allows allele frequencies in a population to change constantly. Remember: evolution is not just about one species changing into another, although…)
What is speciation? Speciation is simply the formation of new species. The traditional definition of a species is a group of organisms that is incapable of breeding with another species to produce viable, fertile offspring. Of course there are a lot of gray area surrounding that definition where ligers and camas lurk. Nature so seldom conforms to our need for rigid definitions.
In any case, new species can form whenever populations of the old species are separated and prevented from sharing genes. Over time their genes diverge and their traits change. Over millions or billions of years, little differences become big differences. Entirely new groups of organisms arise to fill in every nook and cranny of habitable space on Earth. Four billion years later, you have an incredible diversity of life brought about by the fact that genes can change and survival is a constant struggle.
So yeah…all of these things are related to evolution. I can’t imagine why anybody would suggest otherwise, unless they were backed into a corner by mountains of evidence but still could not bring themselves to admit that evolution is real.