Gulf Today - Panorama

Animals can do math


- By Natalie Angier

Every night during breeding season, the male túngara frog of Central America will stake out a performanc­e patch in the local pond and spend unbroken hours broadcasti­ng his splendour to the world.

The mud-brown frog is barely the size of a shelled pecan, but his call is large and dynamic, a long downward sweep that sounds remarkably like a phaser weapon on Star Trek, followed by a brief, twangy, harmonical­ly dense chuck.

Unless, that is, a competing male starts calling nearby, in which case the irst frog is likely to add

two chucks to the tail of his sweep. And should his rival respond like-

wise, Male A will tack on three chucks.

Back and forth they go, call and raise, until the frogs appear to hit their respirator­y limit at six to seven rapid-ire chucks.

The acoustic one-upfrogship is energetica­lly draining and risks attracting predators like bats. Yet the male frogs have no choice but to keep count of the competitio­n, for the simple reason that female túngaras are doing the same: listening, counting and ultimately mating with the male of maximum chucks.

Behind the frog’s surprising­ly sophistica­ted number sense, scientists have found, are specialise­d cells located in the amphibian midbrain that tally up sound signals and the intervals between them.

“The neurons are counting the number of appropriat­ely timed pulses, and they’re highly selective,” says Gary Rose, a biologist at the University of Utah. If the timing between pulses is off by just a fraction of a second, the neurons don’t ire and the counting process breaks down.

“It’s game over,” Rose says. “Just as in human communicat­ion, an inappropri­ate comment can end the whole conversati­on.”

The story of the frog’s neuro-abacus is just one example of nature’s vast, ancient and versatile number sense.

Scientists have found that animals across the evolutiona­ry spectrum have a keen sense of quantity, able to distinguis­h not just bigger from smaller or more from less, but two from four, four from 10, 40 from 60.

Orb-weaving spiders, for example, keep a tally of how many silkwrappe­d prey items are stashed in the “larder” segment of their web.

When scientists experiment­ally remove the cache, the spiders will spend time searching for the stolen goods in proportion to how many separate items had been taken, rather than how big the total prey mass might have been. Small ish beneit from

living in schools, and the more numerous the group, the statistica­lly better a ish’s odds of

escaping predation. As a result, many shoaling ish

are excellent appraisers of relative head counts.

Guppies, for example, have a so-called contrast ratio of 0.8, which means they can distinguis­h at a glance between four guppies and ive, or eight

guppies and 10, and if given the chance will swim towards the slightly ishier crowd.

Attitudes about animal numerosity have changed greatly since the mid20th century when many researcher­s believed only humans had enough gray matter to think quantitati­vely. They cited as an object lesson the 1907 case of Clever Hans, the horse that supposedly could solve arithmetic problems and would tap out his answers by hoof; as it turned out, he was responding to unconsciou­s cues from the people around him.

Since then, researcher­s have approached the ield with caution and

rigor, seeking to identify the speciic evolutiona­ry

pressures that might spur the need for numeric judgments in any given species.

Social carnivores like spotted hyenas, for example, live in ission-fusion

societies, collective­ly defending their territorie­s against rivals but in ever-shifting groups of widely roaming members. “You can never predict who you’ll ind in

which group,” says Sarah Benson-amram, an assistant professor of zoology and physiology at the University of Wyoming. “You might be alone or in a group of 10.”

Chimpanzee­s are social scorekeepe­rs, episodic warriors and number ninjas, too. They can be taught to associate groups of objects with correspond­ing Arabic numerals up to the number 9 and sometimes beyond — three squares on a computer screen with the number 3, ive squares

with 5, and so on. They can put those numerals in order.

The numeric working memory of young chimpanzee­s is astonishin­g: lash a random scattering

of numerals on a screen for just 210 millisecon­ds — half an eye blink — and then cover the numbers with white squares, and a numericall­y schooled young chimpanzee will touch the squares sequential­ly to indicate the ascending order of the numbers hidden beneath.

Don’t bother trying to do this yourself, Tetsuro Matsuzawa, a primatolog­ist at Kyoto University, says at the scientiic meeting in London on which the themed journal was based. “You can’t.”

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 ??  ?? Scientists have found that animals across the evolutiona­ry spectrum have a vast and keen number sense.
Scientists have found that animals across the evolutiona­ry spectrum have a vast and keen number sense.

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