SCIENCE

You would think that someone would have come up with the definitive answer by now, but, in fact, the reason zebras have stripes remains a biological mystery. Scientists have a pretty good idea, however. (New Yorker)

Use our resources to read between the lines of evolution and natural selection.

Discussion Ideas

• Read the fascinating New Yorker blog post, then read the first page of our short encyclopedic entry on adaptation. Are a zebra’s stripes an adaptation? If so, are they a structural or behavior adaptation?
  • Zebra stripes are definitely an adaptation. Stripes were originally a mutation, or genetic change, in a zebra’s fur. Due to the helpful nature of the mutation, it was passed down from one generation to the next. (Or, as the New Yorker blog puts it, the stripes were “some sort of advantage that allowed [zebras] to reproduce more prolifically than their unstriped brethren.”) As more and more zebras inherited the mutation, the mutation became a typical part of the species—an adaptation.
  • Zebra stripes are definitely a structural adaptation, meaning they are a physical part (fur) of the animal itself.

• What are some of the competing ideas for why stripes were such a helpful mutation for zebras—in other words, why did zebras get their stripes?
  • camouflage? Maybe stripes allowed zebras to blend in with savanna vegetation—or each other—so that predators couldn’t see them.
  • distraction? Maybe stripes make it hard for predators to judge a zebra’s speed and distance when it’s running.
  • attract mates? Maybe stripes make zebras more attractive to potential mates. Birds, for instance, have evolved ridiculously beautiful structural and behavioral adaptations for just this purpose.
  • recognition? Maybe stripes allow herd members to recognize each other.
  • cooling off? Maybe stripes somehow protect against the excessive African heat.
  • insect repellent? Maybe stripes discourage disease-carrying flies from biting.

• According to the New Yorker blog, the insect-repellent theory has the strongest support. What advantages would repelling insects have for zebras?
  • “Discouraging bites from flies is obviously useful, since the insects often carry fatal diseases. Also, while a single bite from blood-eating flies extracts just a tiny droplet of blood, thousands of bites per day can add up to significant blood loss.”

• OK, so scientists have a pretty good idea about why zebras got their stripes: flies and other insects don’t particularly like landing on striped surfaces. So, now the question is: Why don’t flies like landing on stripes?
  • Is “not landing on stripes” an adaptation?
    • Yes, it’s a behavioral adaptation. At some point, flies that landed on single-color organisms were more successful at passing on their genes than flies that landed on striped surfaces.
  • What might be some advantages of landing on single-colored surfaces?
  • How would you test your theories?