Why are some animals black and white?

Episode Summary

Executive Summary: This episode of Crowd Science explores why some animals are black and white, using listener Jude's question as a springboard. Host Caroline Steele visits a zoo with guide Johan Bryce to examine zebras, pandas, skunks, ring-tailed lemurs, and penguins. Experts reveal diverse evolutionary reasons: zebras' stripes deter horseflies, pandas' coloration provides camouflage in snowy forests, skunks' patterns warn predators, lemurs' tails aid social signaling, and penguins' tuxedos serve multiple functions like thermoregulation and camouflage. The episode concludes that there is no single reason for black-and-white coloration; each species' pattern evolved for its unique ecological needs.

Main Topics: Zebra Stripes and Insect Deterrence (Priority: 5/5): Martin Howe's research shows zebra stripes confuse horseflies by disrupting their visual resolution, making the zebra appear as a grey blob from a distance and a high-contrast pattern up close, which the flies avoid. Panda Camouflage in Snowy Habitats (Priority: 4/5): Tim Carrow explains that giant pandas' black-and-white coloration camouflages them against snowy, rocky backgrounds in western China, making them hard to spot at a distance despite their striking appearance in zoos. Skunk Warning Coloration (Priority: 4/5): Skunks use their black-and-white stripes as a warning to predators about their ability to spray foul-smelling secretions. The stripe width varies with predation pressure, supporting this aposematic function. Social Signaling in Ring-Tailed Lemurs (Priority: 3/5): Ring-tailed lemurs raise their black-and-white striped tails vertically when moving as a group, acting as a visual signal for cohesion, similar to a tour guide's flag. Penguin Tuxedo: Multiple Hypotheses (Priority: 4/5): Penguins' black-and-white coloration evolved about 14 million years ago. Theories include camouflage from above and below, thermoregulation, and mechanical resistance from melanin, but no single explanation is definitive. No Universal Reason for Black-and-White (Priority: 5/5): Experts emphasize that each black-and-white animal has evolved its pattern for different reasons—camouflage, warning, signaling, or insect avoidance—and humans should not assume a common denominator.

Key Arguments: Zebra stripes evolved to deter horseflies, not mosquitoes, by disrupting the flies' low-resolution vision and making the zebra appear unappealing as a landing site. Giant pandas are camouflaged in their natural snowy, rocky habitat, contrary to their conspicuous appearance in zoos. Skunks' black-and-white stripes serve as a warning signal to predators, with stripe width varying based on local predation risk. Ring-tailed lemurs use their vertically raised tails for social cohesion, signaling group members to follow. Penguins' coloration likely serves multiple functions including camouflage, thermoregulation, and feather durability, but the exact reason remains uncertain. There is no single evolutionary reason for black-and-white coloration; each species' pattern is adapted to its specific ecological niche.

Data Points: Zebra stripe width: about 3 centimeters - Martin Howe's experiments used rugs with stripes matching this width to test horsefly deterrence. Distance at which flies detect pattern: about 2 meters - Horseflies' low-resolution vision switches from seeing a grey blob to a pattern at this distance. Age of fossil penguin: 36 million years - Fossil penguin Inkayaku parasinensis from Peru was grey and reddish-brown, not black and white. Time when penguins evolved black-and-white: about 14 million years ago - This coincided with global cooling and expansion of Antarctic ice sheets.

Pivotal Quotes: "We originally set out to test whether maybe there were these optical illusions at play. So we did a whole bunch of tests where we tried different patterns of rugs, but it turned out that practically every high contrast pattern, every black and white pattern we used, as long as the pattern was sort of in the same scale of zebra stripe, so about sort of three centimeters or so, kind of blocks of black and white, almost every pattern was really effective at stopping flies." — Martin Howe: Explaining his experiments on zebra stripes and horsefly deterrence. "In the forests of western China, you've got black and white patches of snow and rocks and tree trunks. At certain times of year. And if a slow-moving animal like a giant panda is seen at, say, 50 meters or 100 meters away, it's very difficult to distinguish that as being an animal from the snowy, rocky background in which it's seen." — Tim Carrow: Describing how pandas are camouflaged in their natural habitat. "Basically, if you've studied one black and white animal, you've only studied one black and white animal. And really, there should be no reason to think that the appearance of a killer whale is going to have the same reason as the appearance of a lemur, and they're completely different sorts of ways of living life on earth." — Tim Carrow: Emphasizing that each species' coloration has unique evolutionary drivers.

Implications: Listeners learn that animal coloration is highly adaptive and context-dependent. The episode challenges assumptions about commonality among black-and-white animals, highlighting the importance of studying each species in its ecological context. It also offers practical advice, such as wearing patterned clothing to avoid horseflies.