Number of animals and use zero. How far does the number sense go?
One explanation for the same neural framework that develops in such different minds is simply that it is an efficient solution to a common computational problem. “It’s actually sexy, because it suggests it’s the best way,” said Avargis-Weber. There may be physical or other internal constraints on how the brain processes zero and other numbers. “There may be a very limited number of ways you can build a number-encoding mechanism,” Valortegara said.
However, just because crows and monkeys seem to encode an abstract concept like zero in the same way doesn’t mean it’s the only way. “Different solutions could have been invented during natural history, during biological evolution, to make similar calculations,” Valortegara said. Researchers will have to study other animals to find out. In a paper just published in cerebral cortexFor example, Vallortigara and colleagues have identified a brain region in zebrafish that appears to be related to number, although they have not yet tested the animals’ ability to rate zero.
Bees may also hold some surprises as the basis of their number becomes better understood. In a study published last year, MaBouDi and colleagues showed “that bumblebees count through a completely different strategy” when presented with up to four objects, he said. His findings are believed to suggest that the mechanisms underlying honeybees’ understanding of numbers, including zero, may indeed be very different from what has been observed so far.
But perhaps the most fundamental question about numerical abstraction in the brains of diverse animals is not how the ability works but why it exists. Why do animals have to recognize specific amounts at all? Why has evolution repeatedly made sure that animals can understand not only that four is less than five but “four squares” is somehow the same concept as “four circles”?
According to Vallortigara, one of the reasons may be that the account is ultimately very important. “Animals have to do arithmetic constantly. Even simple animals,” he said. “If you have an abstract representation of the number, it is very easy to do.” Abstraction of digital information allows the brain to perform additional calculations more efficiently.
This is probably where zero fits in, too. If two predators enter an environment and only one leaves, the area remains dangerous. Rugani posits that the animal needs not only to be able to subtract in this case, but also to interpret zero as “the result of a numerical or primitive subtraction made previously”—which the animal can relate to particular environmental conditions. In this case, Rujani said, “When it reaches the lowest value, which is zero, the environment is safe.” When searching for food, zero can designate the need to search in a different location.
Neder, however, is not convinced. He does not see an urgent need for animals to understand zero as a number, because looking at it as an absence is usually sufficient. “I don’t think animals use zero as an amount in their daily lives,” he said.
An alternative possibility is that understanding zero – and counting more broadly – may have arisen simply from the brain’s need to recognize visual objects in the environment. In 2019, when Nieder and his colleagues trained an artificial network to recognize objects in images, the ability to distinguish the number of items arose automatically, apparently as a byproduct of that more general task.
A glimpse into the basic building blocks of mathematics
For Nieder, the presence of the talent for numerical abstraction in animals suggests that “something has already been put into the brains of these animals which may form the evolutionary basis of what in us humans can develop into a complete understanding of the number zero.”
But as impressive as the animals’ achievements were, he asserted that there are fundamental differences between how animals show number perception and how humans do it. We don’t just understand quantities. We associate them with random numeric codes. Neder said that the set of five is different from the number 5, and the empty set is not the same as 0.