An article asks why biology students have misconceptions about science, and it clears up one misconception while implying another. Cool!
Here’s their example of a common error of thinking:
Zebras developed stripes to avoid predators.
That error is incredibly common: it’s the problem of thinking teleologically. Stripes didn’t evolve for a specific goal. The interesting point in the article is that biology students are just as likely to have these misconceptions as non-biology students, but that they are better at arguing for the teleological fallacy, which suggests that biology education is reinforcing the misconceptions. Uh-oh.
But I have to point out that the educators discussing this problem went on to reinforce another misconception, that the stripes are adaptive.
Thinking that zebras got stripes to dodge predators, Coley says, is an example of a misconception arising from a particular type of intuitive thinking: Our minds automatically attribute cause and effect to phenomena or events, even when there might be none.
But evolution doesn’t involve “forward thinking,” or intention—ancestral zebras didn’t sprout stripes to blend in with their surroundings. Rather, given a population of zebra-like animals varying in stripedness, those with abundant verticals had a selective advantage over their plainer relatives: Hence, they were more successful at reproducing, and over time, the stripes prevailed.
Huh. Did you know that there isn’t any good evidence that the stripes give a selective advantage in camouflage? Sure, there are good examples of disruptive color patterns making it difficult for humans to discriminate them against certain backgrounds, but the question is whether zebras with stripes were better able to survive than zebras without. Here’s a paper that says the large predators of zebras don’t care about the stripes.
The century-old idea that stripes make zebras cryptic to large carnivores has never been examined systematically. We evaluated this hypothesis by passing digital images of zebras through species-specific spatial and colour filters to simulate their appearance for the visual systems of zebras’ primary predators and zebras themselves. We also measured stripe widths and luminance contrast to estimate the maximum distances from which lions, spotted hyaenas, and zebras can resolve stripes. We found that beyond ca. 50 m (daylight) and 30 m (twilight) zebra stripes are difficult for the estimated visual systems of large carnivores to resolve, but not humans. On moonless nights, stripes are difficult for all species to resolve beyond ca. 9 m. In open treeless habitats where zebras spend most time, zebras are as clearly identified by the lion visual system as are similar-sized ungulates, suggesting that stripes cannot confer crypsis by disrupting the zebra’s outline. Stripes confer a minor advantage over solid pelage in masking body shape in woodlands, but the effect is stronger for humans than for predators. Zebras appear to be less able than humans to resolve stripes although they are better than their chief predators. In conclusion, compared to the uniform pelage of other sympatric herbivores it appears highly unlikely that stripes are a form of anti-predator camouflage.
We always just assumed that they must have a purpose, which is another fundamental misconception.
It’s also possible that they might provide an unexpected selective advantage. Here’s another paper that rejects many familiar assumptions about zebras.
Despite over a century of interest, the function of zebra stripes has never been examined systematically. Here we match variation in striping of equid species and subspecies to geographic range overlap of environmental variables in multifactor models controlling for phylogeny to simultaneously test the five major explanations for this infamous colouration. For subspecies, there are significant associations between our proxy for tabanid biting fly annoyance and most striping measures (facial and neck stripe number, flank and rump striping, leg stripe intensity and shadow striping), and between belly stripe number and tsetse fly distribution, several of which are replicated at the species level. Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss. A solution to the riddle of zebra stripes, discussed by Wallace and Darwin, is at hand.
That concluding sentence is probably too optimistic. What they have is a biogeography argument by correlation: stripy equiids are found in areas with serious problems with tse-tse fly infestations. Not explained is why small biting flies would avoid stripes (they cite a 1930 paper that says they avoid striped surfaces, but I don’t have access to it, and they do show some data that flies avoid landing on narrow stripes), or why stripes aren’t ubiquitous in other victims of flies. I think it ignores the fact, though, that short-lived, numerous flies are going to be more subject to natural selection, so wouldn’t a mutant fly without stripe aversion thrive in an area with lots of stripey meals walking around? It’s plausible, though, and I can believe that the biggest misery in the day-to-day live of a zebra is not getting chased by lions, but having to deal with clouds of parasites.
So it’s safe to say “zebras developed stripes to avoid predators” is completely false in multiple ways. It’s better, but still probably wrong, to say “zebras with stripes were less likely to be eaten by predators, and so left more progeny in the next generation”. It’s more likely that “zebras with stripes were less afflicted by biting parasites, and so left more progeny in the next generation”.
Not considered yet is the explanation that “equiid skin patterning mechanisms make expression of stripes relatively easy, and chance variation in pigmentation will produce species that differ in their degree of stripeyness.”