"It's just an ordinary observation that anyone could make, and yet apparently it wasn't known to science." "I've spent a lot of time handling horses, and having them put their head down to eat, and up to look around, and so on, and I had never noticed this," says Jenny Read, a vision scientist at Newcastle University in the United Kingdom. "And that's kind of remarkable, because the eyes have to spin in opposite directions in the head." "When they pitch their head down, their eyes rotate in the head to maintain parallelism with the ground," says Banks. When the researchers went to watch the animals in action, they discovered something unexpected. And creatures like horses and sheep are constantly pitching their heads down to graze. This trick would only work if the animal's pupils were parallel with the horizon. That makes sense, he says, because it gives prey animals a panoramic view, so they can best scan all directions for danger.īut then the scientists began to wonder. Meanwhile, he says, if you're the kind of animal that gets hunted, "you're very likely to have a horizontal pupil" and to have your eyes on the side of your head. In general, round pupils seem to be common in taller hunters that actively chase down their prey, says Banks. "So for example foxes, in the dog lineage, have vertical pupils, but wolves have round pupils," he says.Īnd while a small pet cat has vertical slits, Sprague says, "the larger predators, like lions and tigers, have round pupils." He says these predators need to accurately judge the distance to their prey, and the vertical slit has optical features that make it ideal for that.īut that rule only holds if the animal is short, so its eyes aren't too high off the ground, Sprague says. That's the kind of animal who lies in wait and then leaps out to kill. "If you have a vertical slit, you're very likely to be an ambush predator," says Banks. In the journal Science Advances, the scientists report that there's a strong link between the shape of an animal's pupil and its way of life. When they pulled everything together, a clear pattern emerged. One of the researchers, Bill Sprague, also at the University of California, Berkeley, says some animals have such dark eyes, it's hard to even see the pupil. For example, was it predator or prey, and active during the day or night? They noted the pupil shape and the location of the eyes on the head, plus the animal's lifestyle. The researchers gathered information on 214 species. "So they're either vertical, horizontal or round." "We restricted ourselves to just pupils that are elongated or not," Banks explains. They looked at just land animals, and just three kinds of pupils. It's the first thing you see about an animal - where their eye is located and what the pupil shape is."įor their recent study, Banks and his colleagues decided to keep things simple. "It's been an active point of debate for quite some time," says Banks, "because it's something you obviously observe. ![]() Needless to say, scientists want to know why all these different shapes evolved. Shots - Health News How Animals Hacked The Rainbow And Got Stumped On Blue
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