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featured essay: july 2002 Kids' Gateway to Understanding Natural Selection: The Peppered Moth by Dale McGowan Last month's essay suggested that the wonders of the actual universe far outshine the wonders of the mythic imagination. So why does humanity prefer the less splendid fictions? There are three primary reasons, though too often we recognize only the first: 1. Myths provide comforting answers to existential questions. 2. Cultural myths are generated internally, from the experience of being human, and so are naturally comprehensible to the creatures whose psychic profile was the basis for them. Natural reality is external in its origin; it is discovered, not created by us, and therefore may initially feel more foreign, less congruent to our psyches. 3. Because of this quality of "discoveredness" instead of self-creation, the wonders of the natural world rarely reduce to sound bytes. They take a bit more effort to understand --- effort few are willing to expend, especially given #1 and #2. Why look for answers that are a bit harder to understand when they can also be less comforting, more foreign? Rhetorical question, of course. One of the most profoundly beautiful achievements of the human mind has been the discovery of our own origin. Like so many of the great achievements of the intellect, the fact that it happened at all --- especially given the morass of human superstition and intellectual laziness out of which it emerged --- is nearly as beautiful as what it reveals. But not quite, in this case, for what could rival the knowledge that all living things are members of one family, directly linked by descent? Nothing I've found comes close. It is so lovely, in fact, that a moment's reflection does away with most of the concerns of comfort and psychic congruency. Compared to the finality of death, evolution is a relatively comfortable pill to swallow. So why the resistance? It's number three: the effort required to understand. Evolution yields macroscopic results from microscopic events arrayed over incomprehensible spans of time. Once it is understood, though, it can be seen for the fairly simple, elegant, and inevitable process it is. But that understanding takes a little time, a little willingness, and some expenditure of brainpower. If the average adult isn't willing or able to understand how evolution works, how can kids possibly hope to? That first step is a doozy. Every descriptor seems to pop strange images into the mind's eye. "Well, Billy, your distant relatives were apes." Guaranteed to make Billy look sideways at Grandma, misreading the scale of time involved. Try again. "Billy, people gradually changed from apes into humans." Not exactly correct, for one thing, and now he pictures it happening in a single lifetime --- one person getting a little less hairy every day. The youngest child's limitations resemble those of the religious fundamentalist in some respects, and for the same reasons: limited experience, limited frame of reference, limited practice in critical thinking, a relatively cartoonish conception of reality. The answer is twofold: find a non-human example and a shortened timescale. Now evolution itself requires thousands of generations and a massive timescale, so above the microbial level we can't see it in action. But we can study natural selection, which is the mechanism by which evolution occurs. Once natural selection is understood, evolution can be seen as an inevitable consequence of the passage of time. And one creature in particular is just waiting in the wings, so to speak, to explain natural selection to our kids: the peppered moth. Tiny school bells may be ringing in your head if you had a decent eighth-grade science teacher. The peppered moth is the single most often quoted example of natural selection in action. It's easy to understand and so clear in its implications that kids tend to vibrate with excited realization as they work their way through the story. Here 'tis, simplified for kid consumption: There's a moth in England called the peppered moth. Two hundred years ago, most peppered moths were light grey with dots of black and brown all over them. They looked like someone had peppered them. That worked out just fine for these moths --- it made them blend in with tree bark so it was hard for birds to find them and eat them. But there were also a few peppered moths who didn't look peppered at all: they were completely black. But only a few. You can probably guess why: the black ones didn't blend in very well, so they were dinner for the birds. If someone has you for dinner, you aren't going to have too many babies, of course. And since the black moths were being eaten most, there were never too many black baby moths being born. Then something interesting happened. Big factories were built in the town near the moths' forest. Dark black smoke belched out of huge smokestacks, making the air near the town very dirty. In fact, the bark on the trees in the moths' forest turned completely black from the dirty factory smoke. That made things a little different for the moths. Now the BLACK moths were almost invisible on the black tree trunks, and the light-colored peppered moths were so easy to see... well, maybe you can guess what happened. Birds only eat what they can find, so who were they eating now? That's right: the LIGHT-COLORED ones! The black moths were probably pretty happy about this: now more of their babies could be born and stay safely hidden from the birds on the black tree trunks. About twenty years later, people noticed that almost ALL of the moths in the forest were black. Now only a few were light grey. The peppered moth had been changed, all because its environment changed. You can tell the story in a dozen ways, depending on the age and level of your child, but some kids as young as six excitedly follow its logic and grasp its implications. Ask what they think will happen to the moths if the factory closes and the black soot washes off the tree trunks (which did, in fact, end up happening, with the expected phenotypic rebound). Ask if they think one color of moth would ever disappear completely. Tell them the whole process is called "natural selection" and ask if it makes sense. Ask if they think this only happens to moths, or might it just apply to lizards as well, or hippos, or (gasp) ...humans? This isn't exactly evolution, of course: it's the first step, natural selection. And armchair logic combined with the fossil record leads to an inescapable conclusion: natural selection plus sufficient time produces evolution. The original peppered moth studies, published by British scientist J.W.H. Harrison in the journal Nature in 1927, were immediately challenged. Darwinian and Lamarckian evolutionists battled with each other and with simple mutationists to determine which mechanism was at work. Several researchers pointed to uncontrolled variables and other methodological flaws in the original study. Today's creationists --- selective as always in their attention and unaccustomed to the scientific method --- see these scientific debates as evidence that the study is without merit. This is, of course, the way science proceeds, and when the smoke had cleared, multiple studies had replicated and strengthened the results, including work in the 1950s in multiple forest areas by E.B. Ford and David Kettlewell at Oxford. It now stands firm as one of the great accurate and graspable examples of natural selection at work --- and simple enough for a child to follow. You'll still find plenty of religious fundamentalist sites on the Internet claiming the peppered moth has been dethroned, of course. Check them out if you are so inclined. In general, though, I'd recommend spending your time with minds that are still capable of working with complex ideas and reveling in the wonder of them. In other words, skip the fundamentalists --- stick with children. There are many, many outstanding websites with various types of good information on the peppered moth and other evolution topics. For the kids, there's nothing better than the following section of this month's Editor's Choice link: http://www.enchantedlearning.com/subjects/butterfly/glossary/pepperedmoth.shtml For homework help on all areas of evolution, go to: http://animals.about.com/cs/evolution/ To prepare yourself on the topic, or to learn precisely why creationist arguments against the validity of the peppered moth example are fallacious, three sites: http://biocrs.biomed.brown.edu/Elephant%20stuff/Chapters/Ch%2014/Moths/Moth-Update.html http://www.talkorigins.org/faqs/evolution-definition.html http://genbiol.cbs.umn.edu/peppmoth/peppmoth.html And to take a look at recent confirmatory research, an excellent, brief article: http://www.wm.edu/wmnews/research/evolution.html |
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