Last week, I discussed the misconception that everything is adaptive. This week, I want to talk about ways we can help our students see and appreciate the wonder of life without their adaptation-everywhere goggles on.
At the younger grades, I’d simply try to watch how I present characteristics of organisms, being careful not to suggest that everything has a purpose. A simple change from asking, "What's that [structure/trait] for?" to "What does that [structure/trait] do?" might even help alter the misconception foundation just enough to make a difference.
Then, in middle school, I’d explain that while many traits are adaptations, some aren’t. A simple example like the belly button would help to illustrate this point. (Be prepared to explain that while belly buttons do indeed collect lint, they were not selected by natural selection for that function!) This would also be a good time to point out that “adaptation” has a common use meaning, as in “We adapt to the heat of summer by wearing shorts,” but this sort of "adapting" is not the same as saying that living things have adapted in an evolutionary sense. For one thing, wearing shorts isn’t heritable!
Then, in high school, I’d emphasize the criteria for an adaptive trait and work through some examples. A body builder’s giant muscles: Heritable? No. So, not an adaptation. Belly buttons: Heritable? Check. Functional? Nope. Ergo: not an adaptation. Male nipples (come one, everyone will love this one!) Heritable? Check. Functional? Nope. Survey says! Not an adaptation. Blood’s redness: Heritable: Yes. Functional: No. Not an adaptation.
Once the ideas have been established, explain that when it comes to functionality, the context matters. For a trait to be an adaptation for a particular function, it must be a consequence of selection for that function. Illustrate this concept with a couple more examples. Forearm feathers in birds: Heritable? Yes. Functional: Yes, can’t fly without them! Increase fitness: Yes. An adaptation? Well, that depends. Adaptation for flight? No. Feathers first appeared on the forearms of flightless bird ancestors, so the basic forearm feather cannot have been an adaptation for flight. Adaptation for insulation? Most likely. Now, can you say that asymmetrical feathers are an adaptation for flight? Yes. This type of feather seems only to be associated with birds that fly, or whose ancestors flew.
Male peacock tail feathers: Heritable: Yes. Functional: Yes—Although they certainly do no favors when it comes to effective flying or avoiding detection by predators, they help males attract mates. Increase fitness: Definitely. So, are they an adaptation? Yes, a classic example of an adaptation for mate attraction shaped by sexual selection.
Human tailbone: Heritable: Yes. Functional? Well, certainly not for its original function. In ape ancestors, what we now know as “the tailbone” made up the first few bones in the extension of the vertebral column that supported a tail. So this one is a nice example of a vestigial structure. It no longer serves the function for which it was originally acted on by natural selection.
In general, if your students ask you, “What is this for?” ask back, “Does it have to be for something? And do you mean what was it for originally, or what is it for now?” Try to get them to understand that structure/traits can do many things, but that doesn't mean that they were selected for those functions. Explain that sometimes, traits aren’t adaptive at all (as in belly buttons), and sometimes, adaptive traits take on new adaptive roles (as in forearm feathers), and sometimes traits lose their original adaptive function (as in human tailbones).
I’ll close this one out with a quote from Stephen Jay Gould. As a slight aside, I've loved writing about this topic because it's given me an excuse to dig back into Gould's writings. He was such a master of science communication, making the complicated accessible without being condescending or committing errors-by-oversimplification. Any teachers looking for sources of material to help cover new science/technical subjects Common Core standards should take a look at his "This View of Life" essays that appeared in Natural History. In this one, Gould writes about an exchange with Francis Crick:
“I well remember something that Francis Crick said to me many years ago, when my own functionalist biases were strong. He remarked, … ‘Why do you evolutionists always try to identify the value of something before you know how it is made?’… Now, having wrestled with the question of adaptation for many years, I understand the wisdom of Crick’s remark. … we must first establish ‘how’ in order to know whether or not we should be asking ‘why’ at all.”
I can't really sum it up better than that.