A leopard may not be able to change its spots, but some zebras change their stripes. Zebras in warmer places have more stripes, a new study shows, which might help answer an age-old question: Why stripes?

The answer probably comes down to keeping zebras cool and fending off disease-causing insects that are more common in hotter climates, researchers reported Tuesday in the journal Royal Society Open Science.

All three species of zebra have bold black and white stripes that stand out among more drab-looking African grazers, like buffalo and antelope, especially against a plain savanna background. And standing out would seem to make a zebra more likely to become a lion's lunch.

This "stripe riddle" has puzzled scientists, including Darwin,