Your Cat and Evolution
This week’s just-so story is, “How the kitty got its stripes.” All the news are on it; they just don’t answer the question.
News media are not the least embarrassed to invoke the Kipling just-so story formula, “how the x got its y.” In this week’s iteration about cat stripes, Live Science headlined, “How the tabby got its stripes.” Science Daily was a little more creative (or verbose) with, “How the Sub-Saharan Cheetah Got Its Stripes: Californian Feral Cats Help Unlock Biological Secret.” Even the prestigious journal Science‘s news site got into the act with, “How the Tabby Got Its Blotches.”
What the original paper in Science found were genes in tabby cats that, when mutated, form blotches rather than stripes. Then the research team checked mutant cheetahs with blotches and found the same mutation. That’s about all. The paper is by Kaelin et al., in Science, “Specifying and Sustaining Pigmentation Patterns in Domestic and Wild Cats” (21 September 2012: Vol. 337 no. 6101 pp. 1536-1541, DOI: 10.1126/science.1220893). The most detailed summary was on Science Daily, echoing a Stanford press release, “How the Cheetah Got Its Stripes: A Genetic Tale by Stanford Researchers” (there they go again).
“We were motivated by a basic question,” said Barsh of the turn to the study of big (and little) cats. “How do periodic patterns like stripes and spots in mammals arise? What generates them? How are they maintained? What is their biological and evolutionary significance? It’s kind of surprising how little is known. Until now, there’s been no obvious biological explanation for cheetah spots or the stripes on tigers, zebras or even the ordinary house cat.”
That’s about all that was said by anyone about evolution: only questions. None of the scientists or authors explained how these genes “emerged” in the first place. None of them explained how genes, inside of cells, create precision patterns on the external fur of multicellular mammals. The press release said that many animals, such as fish and insects, have patterns, but they grow them differently: they add more stripes as the animal grows, whereas your kitten’s pattern will remain the same as it grows to adulthood. That was cause for more questions:
“Somehow, cells in the black stripes know they are in a black stripe and remember that fact throughout the organism’s life,” said Barsh. “We were curious about what’s happening at the boundary between light and dark stripes and spots. How do these spots know to grow with an animal?”
Even though it is evident that a cheetah’s sports or a tiger’s stripes aid camouflage, nobody explained why some cats are monocolored, some are spotted, some are striped, and some have chaotic markings with no clear function at all. In short, they promised but did not deliver.
So the question is, does Darwin provide a better explanation than Kipling’s? We learned about a couple of genes, it’s true. We know that mutations create observable changes in the pattern. We know the same mutation found in a tabby cat creates a similar change in a cheetah. But do we know How the tabby got its stripes? No! – not by evolutionary theory, the explanatory toolkit that is advertised as the great principle that makes sense of everything in biology. All we know is that when a cat embryo grows, certain genes are switched on and regulated by other genes. We may know which genes are involved, and how they are regulated, but we still don’t know “How the tabby/cheetah got its stripes.” Moreoever, we don’t know why some animals have them and others don’t.
Think of all the ways Kipling’s story is better than Darwin’s. It’s amusing. It’s entertaining. It can be understood by children. It’s whimsical. It’s fanciful. It has no connection to reality. Wait– we take that back. That’s all true of Darwin’s story as well.