Good Eyesight? Thank Snakes

Aug. 30, 2006 — -- What miracle of evolution gave humans the ability to see details just inches away?

Snakes, says an anthropologist who has spent years trying to answer that question.

Especially venomous snakes that forced our distant relatives to improve their vision or perish.

Lynne Isbell of the University of California at Davis has brought forth a new hypothesis that could explain why humans are equipped with such extraordinary eyesight. It's the product, she says, of a "biological arms race" tens of millions of years ago between primates and vipers.

The primates survived, but the trauma may help explain all these years later why snakes are still reviled by so many humans.

Isbell's theory, published in a recent issue of the Journal of Human Evolution, flies in the face of conventional wisdom and will require much more research to be verified. The current thinking holds that primates developed near-vision capabilities to help them capture bugs, or at least reach out and grab a piece of fruit.

But Isbell points out that when snakes began to eat primates, it made sense for the monkeys and apes of Africa to develop better eyesight. A snake, after all, is pretty harmless unless it's close by. It's not likely to romp across the lawn to attack a human, or even a smaller mammal.

But if it's close, you better be able to see it.

She didn't set out to disprove an old theory, or to rattle the cages of scientists in disciplines as diverse as neurology and primatology. In fact, she was researching a totally different question when evidence she was collecting from around the world led her in another direction.

She decided to change course partly because of an old grudge. While researching primates in Africa, "the leopards kept eating my monkeys," she says. So when the data she was collecting suggested a new theory involving primate predators, she was willing to spend six years of her life delving into subjects she admits she initially knew little about. Like neurology.