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Posted by W von Papineäu on May 07, 2003 at 21:55:39:
NATURE (UK) 03 May 03 Salamanders can do maths - Amphibians hint that number skills evolved early. (Hannah Hoag)
Salamanders, given a choice between tubes containing two fruitflies or three, lunge at the tube of three1. This hints that the ability to differentiate between small numbers of objects may have evolved much earlier than scientists had thought.
Primates can spot the greater of two quantities smaller than four, without any training. Babies choose the bowl with more cookies; monkeys go for the bucket with more slices of apple.
The surprise, says Claudia Uller, of the University of Louisiana at Lafayette who carried out the study, was that the amphibians "failed in the same way that babies and monkeys do" - more than three objects confuses them.
"There is a limit on the number of objects that can be tracked at one time," explains Alan Leslie, who works on human brain development at Rutgers University in Piscataway, New Jersey. The portion of the brain that focuses attention cannot, it seems, deal with more than four objects.
The addition of salamanders to the list of animals with natural mathematical abilities hints that some notion of number evolved at least 28 million years ago. "It may be more ancient than we thought," agrees Marc Hauser, who studies primate math at Harvard University in Cambridge, Massachusetts.
But Hauser and Leslie caution that different processes may be at work in amphibians and primates. In monkeys, for example, some cells of the brain's prefrontal cortex respond to single objects and others to pairs2. The salamanders could be influenced bythe physical volume of the flies or the amount of noise that they make, say.
"It may be a fairly basic sort of mechanism that is highly preserved in evolution," explains Leslie. Or it may have evolved independently, he suggests, like the eye.
References
Uller, C., Jaeger, R., Guidry, G. & Martin, C. Salamanders (Plethodon cinereus) go for more: rudiments of number in an amphibian. Animal Cognition, published online, doi:10.1007/s10071-003-0167-x (2003).
Nieder, A., Freedman, D. J. & Miller, E. K. Representation of the quantity of visual items in the primate prefrontal cortex. Science, 297, 1708 - 1711, (2003).
