December 18, 2020 | David F. Coppedge

How the Story Got Its Just-So

Scientific storytelling can be useful when it’s not a just-so story. What’s the difference?

Without question, people relate to stories. Science, however, is about explanation and testing things. Can these aspects be combined? The answer is yes. At CEH, we often complain about “evolutionary just-so stories” (and so do some evolutionists). What makes them just-so? And how can a just-so story become a good science story? Here, for a change, is a good example.

How cats get their stripes and spots (Elizabeth Pennisi, Science Magazine). Pennisi seems embarrassed that her title is in Kipling just-so story form: “How the camel got its hump” or the like. Her article will quickly redeem itself.

When Rudyard Kipling told how the leopard got his spots, he missed the mark. Leopards have “rosettes”; spots are for cheetahs, says Gregory Barsh, a geneticist at the HudsonAlpha Institute for Biotechnology. But whatever you call the markings, how wild cats and their domestic counterparts acquire them has long been a mystery. Now, Barsh and his colleagues have found an answer. In so doing, they have shown that a 70-year-old theory explaining patterns in nature holds true for fur color in cats, and likely other mammals as well.

The article becomes a mystery story – a scientific Sherlock Holmes short story. So far so good. It becomes even better as Pennisi and the scientists she brings in as characters do something honorable: they stick to empirical observations and hypothesis testing. Off they go, trying to determine the cause of the spots and stripes that people have long wondered about. Only the facts: what happens when this gene is knocked out or mutated? They begin with an old theory by mathematician Alan Turing that certain molecules could enhance or inhibit one another as they spread through a tissue. That served as a heuristic idea; can it survive the rigors of testing?

So Barsh’s team turned to domestic cats to track the identity of molecular activators and inhibitors of coat color. A decade ago, they tracked down a gene, Tabby, that, when mutated, gives tabby cats black blotches instead of their usual dark stripes. HudsonAlpha geneticist Christopher Kaelin found that same mutation in king cheetahs whose spots were unusually big and blotchy, suggesting the same genes color both wild and domestic cats.

Credit: Illustra Media, Ode to the Animals

Like many mysteries in science, an answer to one question leads to other questions.

Researchers had already shown the Turing mechanism involving Wnt and Dkk4 sets up the formation of hair follicles—but not coat color—later in mouse development. Barsh’s team, however, found that the color pattern in cats and possibly other mammals is established well before hair follicles appear, suggesting early color patterns may guide hair follicle pigmentation.

That simple interactions among well-known molecules can explain the variety of coat color patterns in mammals is an example of nature’s thriftiness, Headon says. “It suggests that the same molecules and pathways are likely to be reused for patterning of very different structures and at very different scales to form the intricate elements of the vertebrate anatomy.”

The ending may feel unsatisfactory, because it leaves the reader hanging with a high perhapsimaybecouldness index. Pennisi uses the words “may” and “possibly” and “suggests” too many times in the last sentences. There isn’t a complete answer yet. Never in this article, though, do the scientists take the cheap way out of saying, “It evolved.” They know more work needs to be done, but they are striving to connect testable causes to observable effects.

Zebra stripes form elaborate, symmetrical patterns. Credit: Illustra Media.

That’s the secret to keeping the “just-so” out of storytelling: kick Charlie out of the lab, and send his Darwin Flubber out with him. Instead of confabulating in Darwinese, using jargonwocky as fogma to cover incompetence, expecting the emergence of a mythoid by a poof spoof, connect testable causes to observable effects. It’s so easy. Evolutionary biologists should give it a try. [Note for unfamiliar terms, see the Darwin Dictionary.]

Among science journalists, Pennisi is often a breath of fresh air. She doesn’t use Darwinism as a crutch very often. When evolution gets mentioned, she will often point out the problems with it. Science reporting would be better with more like her.

Even so, readers should note that much more needs to be learned about animal patterns than is told here. Many animal patterns cannot be explained by simple diffusion of activators and inhibitors. When you consider a zebra, a tiger, or a butterfly, there is certainly much more going on in the genes and embryo than these hints of suggestions of possible answers provide. From tiny beetles to tall giraffes, from nudibranchs to parrots, animal patterns are exorbitant in their complexities and colors. The patterns represent “useless beauty” that is gratuitous, as Nelson and Gauger say in the end of the film Metamorphosis. Restricting one’s explanation to natural causes might be as vain as looking for laws of nature to explain a work of art. Just so you know.

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