Humans are not the only ones to count from left to right. Researchers in Italy found that mental number lines, where numbers rise from the smallest on the left to the largest on the right, come naturally to newborn chicks too.
In experiments at the University of Padua, three-day old chicks were trained to find food behind a panel bearing five bright spots. Once they had become familiar with that, they were confronted with two panels bearing different numbers of spots.
Footage of the chicks showed that when faced with panels that had only two spots, the birds consistently looked behind the left of the two panels. But when faced with eight spots on each panel, they went poking around the righthand panel.
The researchers repeated the experiment with a different set of numbers and found that the chicks again went right for higher numbers and left for lower ones.
Rosa Rugani, who led the study, said the findings suggest that newborn chicks might share the human tendency to map numbers in space, from the lowest on the left, to the highest on the right.
Writing in the journal Science, she argues that the ability probably evolved millions of years ago, before human ancestors split from those of modern birds. “During evolution, the direction of mapping from left to right rather than vice versa, although in principle arbitrary, may have been imposed by brain asymmetry, a common and ancient trait in vertebrates, prompted by a right hemisphere dominance in attending visuo-spatial and/or numerical information.”