Counting is not unique to humans: a huge range of animals understand numbers, from salamanders to honeybees
While working in Louisiana, psychologist , of the University of Essex, UK, tested the numerical abilities of a local amphibian, the .
When tasked with picking between two fruit-fly-filled tubes, the animals could tell the difference between 1, 2 and 3 flies, but not between 3 and 4.
They also discriminated between larger numbers of flies; up to 16 so far.
However, they could only do this if the ratio between the number of flies in each tube was greater than 2 to 1.
(Image: Brian Gratwicke)
Experiments in newborn chicks show that they have an innate sense of number.
A team lead by and , at the University of Padova, Italy, found that chicks duped into believing balls or scraps of paper are their kin can perform simple addition and subtraction.
(Image: Rosa Rugani / University of Trento)
Clever Hans was a German horse that wowed European crowds in the early 1900s.
He was apparently able to stamp out the answers to maths problems.
However, a scientific trial later proved that Hans was reacting to the subconscious body cues of his trainer, and .
can be tricked into raising the eggs of other coots.
To combat this, they only add up their own eggs when determining how many more to lay – ignoring any rogue eggs that may have turned up.
(Image: , Edmonton, Alberta)
Overwhelming evidence now suggests that other primates have a sense of number that is similar to our own.
For instance, when tasked with picking the larger of two groups of dots flashed onto a computer monitor, and university students both make fewer errors when the ratio between the two groups of dots is large.
“The student’s performance ends up looking just like a monkey’s. It’s practically indistinguishable,” says , a psychologist at Duke University, who led many of the studies.
(Image: Wally Koscielny / )
also seem to rely on ratio in order to count.
and colleagues at the University of Padova found that, when tasked with swimming to the larger of two shoals, the fish can discriminate .
However, they can only do so if the ratio between the fish in each shoal is greater than 2 to 1.
They also represent smaller numbers precisely, discriminating between 1, 2, 3 and 4.
(Image: Christian Agrillo / University of Padova)
has been leading the research into the cognitive behavior of lemurs, including showing that they can perform numerical cognition.
Brannon uses a mix of computer touchscreens (left) and physical, sequential experimenter tests.
She has shown that have numerical representations that are modulated by – an equation that attempts to describe how changes in the real world (like the size of a number) are reflected in changes in perceived, subjective intensity.
She has also shown that ringtailed lemurs () can represent ordinal relations – that is, put numbers in order of size – much like monkeys.
(Image: Elizabeth Brannon / Duke University)
are the first insect shown to exhibit a sense of number.
and colleagues that bees could learn to distinguish between groups of 1 and 2 geometric shapes to receive a sugar reward.
They can also apply that knowledge to tell the difference between 2 and 3, and 3 and 4. 5 seems to be their limit.
(Image: Jeremy Bright / Robert Harding / Rex Features)
Read more: Animals that count: How numeracy evolved
