I don’t understand how computers find each other over the Internet, so I must be hallucinating this message board. And nobody really understands for certain how gravity works (exchange of gravitons, the existence of which has never been conclusively demonstrated? fluctuations in the ninth dimension of superstring interconnections?), so we’re all imagining that we’re stuck to the ground; mass collective hysteria prevents us from admitting we’re all floating in deep space.
Punctuated equilibrium is very, very easy to understand. Imagine a colony of mice. They live in a valley, isolated from other types of mice. The weather, precipitation, and so on are mild and unchanging within a narrow band of variation. The mice are very well adapted to this environment. Constant mutations arise in baby mice, as they do in all species, but none of them provides an advantage; the mice are about as well adapted as they’re going to get. Hence, the mutations never take hold, because they don’t help, and the mice stay the way they are. State: Equilibrium.
Then something changes, quick and sudden. Say Mt. St. Helens blows up a mile away. It had formerly created a wind block against the valley; now it isn’t there, allowing different wind patterns and climatic influences to reach the valley. The valley is seeded with a hardy plant, say a grass, that the mice have never had to deal with before. The grass is tough and thick, and the mice have trouble navigating through it. The grass takes over the valley quickly, and the mice, struggling with it, begin to die off, unable to escape predators or locate food.
Constant mutations still crop up in the baby mice, at the same rate as before. Now, though, the mice are not as well adapted to their changed environment, and any differences in the baby mice that provide an advantage will naturally take hold. Say a few baby mice are born who have longer legs and tougher claws, which allows them to get slightly higher in the grass and dig through it more effectively. These mice will survive better than their parents, and those traits will take over. If there are enough of these new mice (i.e. if the whole species doesn’t die out), they will fairly quickly, within a few generations, replace the old variety. And if nothing else changes, this new variety will take over the valley, and equilibrium returns.
See how it works? (1) Species is well-adapted; mutation/changes don’t provide advantage, and don’t catch on; equilibrium is maintained. (2) Something changes, making the species less well-adapted, and the mutation/changes potentially may create an improvement. (3) If they do, the new variety takes over, and equilibrium returns.
Equilibrium – punctuation – back to equilibrium. Not that hard.
We have definitely seen this in nature. The classic example is in England during the industrial revolution, when white moths turned into black moths in just a few years. There was also a researcher on a South Pacific island who watched lizard feet change in an equally short timeframe in response to similar outside stimuli, specifically a change in flora creating different-thickness branches the lizards would have to climb to pursue their insect prey. (Cite: Scientific American. I’d have to dig to find the issue.)
Now look at it in the broad scale. Continents are drifting. Some lemur species on an isolated peninsula is perfectly happy for the fifty thousand years its land mass is in a given climatic belt. Then it crosses some trade-wind barrier, and temperature and precipitation change. Eventually, the lemur has to change to survive. The species doesn’t do this consciously; the constant background mutations just finally find a new environment in which their innovations can take hold, as opposed to being rejected as not superior to the original.
Then the land mass runs into another one, and the lemur species is brought into contact with some other species for the first time, say a large predatory bird that discovers it likes eating the lemurs. Again, the lemurs are forced to change, either by shifting from diurnal to nocturnal or something else that helps them escape predation. And at this point, the lemur may have changed enough to be a different species than it was originally.
Taken in the long view, you can see that, step by step, an animal may evolve far from its progenitors. In addition, punctuated equilibrium answers a lot of nagging questions about the mechanics of evolution.
First, if half the lemur species is left across a channel in their original environment, they’ll have no need to change to adapt. This answers the old question, “If humans arose from monkeys, why do we still have monkeys?” Only the monkeys who moved to a new environment, or whose environment changed around them, needed to change. The rest were perfectly happy, and stayed the way they were.
Second, it suggests not just a reason the lack of transitional forms, but a requirement that there not be many. If evolution isn’t working slowly and gradually, if species change only in response to immediate and urgent need, then those transitional forms will represent a tiny minority of available fossils, during the brief period of change in response to a stressor. The overwhelming majority of fossils will be from the lengthy periods of equilibrium bracketing the comparatively brief periods of change.
Third, it undercuts the external “guided, purposeful” problem, that is, the conception of evolution as a sentient force constantly working to push species to “higher,” more “improved” forms. Species do what they must to survive. Potential changes are always coming up in the form of constant mutation. If the species is well-adapted, they reject those changes. If something modifies their environment, they can begin accepting the changes until they are once again well-suited to their environment. No need for an external guiding hand, shepherding Nature along a self-improvement track.
Also, on another topic: It’s been mentioned in this and other threads that laypeople don’t understand what is meant by a “theory,” that no scientific principle is ever 100% proven, but that years of support and reinforcement can allow thinking people to accept the theory as a guiding principle. Eventually, a theory becomes so well-entrenched, having been bolstered by a hundred thousand confirming experiments, that scientists don’t feel it necessary to confirm the principle the hundred-thousand-and-first time.
Unfortunately, non-scientists who don’t like the findings latch onto this “unproven” moniker, and we get travesties like the Oklahoma disclaimer quoted in the OP. (See? This wasn’t a total hijack.) The bottom line is, if science didn’t work well and reliably, we wouldn’t have automobiles, computers, airplanes, antibiotics, artificial skin, videotapes, telescopes, synthetic fabrics, and uncountable other examples of science as a robust, self-correcting method of learning about the world.
I would hardly expect this to be the last word on the subject of evolution in these seemingly unending debates. However, maybe a few people will grasp the concept of punctuated equilibrium, and how it addresses many of the core concerns of the overall evolutionary mechanism, and maybe then it won’t keep coming up in these debates as a mystery and therefore some sort of an Achilles Heel, which it certainly is not.
