One of the most important things a person can do for her worldview is develop a solid intuition about how evolution works.
To that end, I'm collecting important insights, new perspectives, and myth-debunkings.
It's not clear how important it is to clear these things up. They aren't honest mistakes in a good-faith attempt to understand Darwin's theory. Instead they're propaganda sound-bites slung around by people who are ideologically opposed to evolution (read: Creationists).
Still, while we're at it, it's probably worth a glib sentence or two to dispute each claim:
- Evolution is "just a theory" — and therefore(?) not something that needs to be taken seriously. Everything we do in science is "just a theory." But among all of our scientific theories, evolution is extraordinarily well-supported.
- Evolution isn't science because it's not observable.
- Evolution has never been observed. Well, insofar as it's possible to observe anything as abstract as natural selection, we have. We've observed it in finches, bacteria, fish, ...
- Some structures are too complex to have arisen one small step at a time. "Half an eye (or half a wing) is of no use to anyone." "Irreducible complexity."
- "There are no transitional fossils."
- Evolution violates the second law of thermodynamics. The second law applies only to closed systems, but Earth isn't a closed system: it's continually flooded with energy from the sun.
- Humans were descended from monkeys. First of all, to be technically correct: We aren't monkeys; we're apes descended from a common ancestor that we shared with monkeys some 25-30 million years ago. More importantly: so what if we were descended from monkeys?
Misconception: Individuals can evolve.
Literally, "evolution" just means change — and clearly, individuals undergo a lot of change during their lifetimes. However, in the context of a discussion of how species have changed over millions of years, "evolution" refers not to the changes that any individual organism undergoes, but rather to the changes that happen to a whole population of organisms from generation to generation.
Misconception: Evolution explains the origins of life.
Nope. Darwin's theory of evolution explains only how species change over generations. It doesn't explain how the first lifeforms arose. Scientists have some good ideas about the origins of life, but evolutionary theory isn't part of the explanation.
Misconception: Evolution works for the "good of the species." Natural selection involves species "trying" to adapt. Species evolve on purpose. Natural selection gives organisms what they need.
Nope. Most of the time it's reasonably safe to personify Nature or Natural Selection as an intelligent force that helps species adapt to their environments, but this is one place where personification (as a conceptual shortcut) gets us into trouble.
If we go back to the basics and try to explain what's happening without appealing to the "force" of natural selection, we can clear things up. When we say that a species is evolving, what we mean is that some members of that species are doing a better job surviving and reproducing (i.e., leaving more grandkids) than other members, by virtue of how their genes are different from their rivals. When this happens, the individuals who did more surviving and reproducing left more of their genes to later generations. And thus later generations look like the more successful members of previous generations.
But there was no foresight to this process. There was no goal that Nature had in mind, that she was trying to achieve by weeding some members of the population out. Some members simply got weeded out and didn't leave as many of their genes to later generations — period, end of story.
This is why altruism is so hard to explain. If Nature were like a god, looking down from the heavens and smiting the meanest individuals with lightening in order to benefit the whole species — well, then altruism would be easy to explain. But since Nature isn't an agent with goals, the only way for altruism to evolve is for altruists to (somehow) leave more descendants. [*]
[*] Technically there's another way — kin selection — but that's more complicated and, according to one of its original proponents, probably doesn't work.
For this reason, many people have called natural selection a "blind, dumb force." This is true, at least to a first approximation. We'll see how it's slightly misleading in a minute.
Misconception: Natural selection leads to ever-greater complexity.
Misconception: Evolution takes a very, very long time.
Misconception: Evolution is random, works completely by chance.
Misconception: The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest.
Misconception: Natural selection produces organisms perfectly suited to their environments.
Misconception: All traits of organisms are adaptations.
Misconception: The ladder of progress.
Humans are the pinnacle of evolution. Humans are more advanced ("more evolved") than other species. Organisms are always getting better. ("Ladder of progress.") Evolution results in progress; organisms are always getting better through evolution.
Complexity from simple rules
Conway's Game of Life
The importance of parasites
Misconception: Evolution is a blind, dumb force.
If you've ever boggled at how something as wonderful, complex, and intelligent as a human being could arise out of such a simple (not to mention random and chaotic) process as natural selection — well, then you don't have the right intuition for what's been going on here.
While it's true that Nature has no foresight, she's not "unintelligent." As Alan Watts says:
You cannot get an intelligent organism, such as a human being, out of an unintelligent universe.
Our evolved intelligence implies that our environment (technically, our ancestors') was complex enough to require us to become intelligent. If the environment were simple or stupid, we wouldn't have needed big messy brains to navigate it.
It's only because we were surrounded by intelligent predators, intelligent parasites, and other intelligent humans that intelligence was rewarded in our ancestors.
This is where the phrase "natural selection" can be misleading. Yes, we were "selected" by "nature," but that doesn't mean just falling rocks and random lightening strikes. We were also "selected" by cunning predators, sophisticated parasites, and (especially in our choice of mates) by our fellow humans.
Viewed this way, evolution starts to look less and less a process of chance survival, and more and more a process of active self-selection. In other words, we weren't shaped, blindly, by "nature"; rather we were shaped, very deliberately, by our own ancestors.
Images and videos
[Would be nice to get a video showing how life intercepts energy from the sun; magnets on a table; we are dust breathed to life by star-wind.]
In the video above, the 1:40 mark (density-dependent fitness landscape) is especially important.
How fast does it work?