I have always wondered why we have not domesticated [zebras] for riding, like horses? —CeeCee Hall, California
Historically, it’s a matter of circumstance that zebras weren’t domesticated—not necessarily because the equines are aggressive, as is commonly thought, said Fiona Marshall, an expert in animal domestication at Washington University in St. Louis. (See “Zebra Stripes Evolved to Repel Bloodsuckers?“)
That’s because the three modern species of zebra—Grevy’s zebra, plains zebra, and mountain zebra—”weren’t in the right place at the right time,” Marshall said, while the African wild ass, the ancestor to the donkey, was. (There are no native horse species on the African continent.)
Asses were domesticated 7,000 to 8,000 years ago, when the Sahara began to turn to desert.
As the environment got drier, cattle herders “started moving, and it was an advantage to have an animal [like an ass] to put their belongings on so you could move whole families at one time.”
Marshall hypothesizes that wild asses benefited from staying near the cattle herders as conditions became increasingly dry. Zebra were not living in the region during this time of domestication.
The African wild ass is also a social animal that will breed in captivity, qualities thought to help make animals able to be domesticated.
These days, though, it is possible to domesticate zebras, she added. (See more of Marshall’s research and watch a video of African wild ass foals born at the St. Louis Zoo.)
What … insect looks like a spider but has six legs and two antenna, a small size, [and is] black in color? —Marge, Mississauga, Ontario
Phillip Koehler, an entomologist at the University of Florida in Gainesville, has a possible answer: “This time of year in Canada, it might be marmorated stink bugs. They look like spiderlings,” Koehler said via email.
“Homeowners may not be familiar with them,” he said. The CBC reports that the stink bugs are an invasive species accidentally introduced to North America in the 1990s. The first official sighting in Ontario was in 2012.
How can it be determined that the [Indian purple frogs, formally discovered in 2003] are an endangered species based on such a short time frame to study their population and habitat? —JohnFLob, NC
Sometimes it seems like the minute we hear about a new species it’s already declared endangered, but many factors go into assessing the risk of extinction.
“We’re not just looking at the species in isolation—we look at what’s going on with a species and where it lives,” said Ariadne Angulo of the International Union for Conservation of Nature’s Red List of Threatened Species, which keeps track of how many species are doing worldwide.
For example, the Western Ghats, where the purple frog lives, is known for species that thrive only in that particular place—like koalas in Australia or lemurs in Madagascar. So if a species is found in only one habitat—especially if that habitat is threatened—it would be considered more vulnerable to extinction. (See National Geographic’s Last of the Last series on endangered species.)
Angulo says another factor is that it takes a long time to formally describe a species, so just because it’s formally announced doesn’t mean that people haven’t known about it.
“It may be that that researcher has been working on that species for five or ten years,” Angulo said.
How do fish check the safety of their environment? The fish I have observed surface, touching the water line with their nostrils, and go down to the bottom to find out if the water level is enough for their safety. —Ali, Shiraz, Iran
Adam Summers, a fish expert at the University of Washington, Seattle, said via email that fish have highly sensitive lines that run the length of their bodies and give them information about their environment.
The animals may surface and go back down for many reasons, but sensing depth isn’t one of them, he added. (See “How Do Glowing Sharks See in the Dark? New Surprises Revealed.”)
In terms of keeping safe, many fish smell predators, and some secrete an alarm substance when they are maltreated.
“Fishes nearby, with the ability to sense this schreckstoff”—which means “scary stuff” in German—”will hide when there is evidence of evil afoot,” Summers said.