Newborn chicks show a human tendency to place numbers in ascending order from left to right, scientists have learned.
In a series of experiments, researchers showed how three-day-old chicks associated low numerical values with space to their left and higher values with space to their right.
The results suggested that the habit of visualising a line − a ‘mental number line’ (MNL) − along which small values are located on the left and high values on the right evolved millions of years ago before the ancestors of humans split from birds.
Spatial mapping of numbers from left to right may be a universal cognitive strategy
The tests began with chicks being familiarised with a particular number of small squares on a panel, behind which they could find a food reward.
They were then presented with two panels, both displaying an identical number of squares that was either smaller or larger than the original, and spaced apart. If the new number was smaller, they tended to investigate the panel on their left as they searched for food.
If it was higher, they were drawn to the one on their right.
The association remained when the relative values of the original ‘target’ number and the numbers on the two panels the chicks had to choose from were altered.
If the target number was five, and the number displayed on the two panels was two, the chicks gravitated to the panel on their left.
But if the target number remained five and eight squares were displayed on the ‘choice’ panels, they instinctively preferred to investigate the right-hand panel.
The researchers, led by Rosa Rugani, from the University of Padova in Italy, reported their findings in the journal Science.
They wrote: “Our results indicate that a disposition to map numerical magnitudes on to a left-to-right oriented MNL exists independently of cultural factors and can be observed in animals with very little non-symbolic numerical experience.
“Spatial mapping of numbers from left to right may be a universal cognitive strategy available soon after birth.”