Why Zebras Got Their Stripes

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.

A zebra's skin is black; only its fur is distinctively striped. The patterns are as unique as fingerprints—no two are exactly alike—although each zebra species has its own general pattern. Photograph by George F. Mobley, National Geographic

A zebra’s skin is black; only its fur is distinctively striped. The patterns are as unique as fingerprints—no two are exactly alike—although each zebra species has its own general pattern. According to the good folks at South Africa’s Kruger National Park, the stripes on this species (Burchell’s zebra) are larger and less numerous than those of its plains cousins. 
Photograph by George F. Mobley, National Geographic

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?

 

  • 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?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s