When it comes to cognition, there are few answers on the origins of many behaviors. Neurobiology and social anthropology help researchers understand the development of speech, the correlation of objects or words with physical entities, and even the emergence of faiths. However, when it comes to something as simple as a number line, which is virtually a universal means of discerning small numbers from larger numbers, researchers are stumped. And looking to nature for the answer, a new study published this week in the journal Science, discovered just how universal these number lines are.
Think that humans are the only creatures capable of simple arithmetic? Well you'd find yourself out of luck if you thought that. Previous studies have linked several species with having the ability to recognize numbers, and the new study conducted by ethologist Dr Rosa Rugani, from the University of Padova, reveals that even newly born chicks can crunch some numbers too. While they may not be carrying the one over, or computing integrations, they chicks are not only able to recognize number patterns but they can also place them in ascending order from left to right-much like humans do on a number line.
Testing the tiny birds' ability for "number mapping", which was once thought of as an advanced cognitive ability, the series of experiments published this week in the journal Science tested three-day-old chicks' abilities to discern higher numbers from lower numbers when confronted will multiple squares representing a given target. By associating the given numbers with food rewards, the newly-hatched chicks began to investigate in search of grainy treats. What researchers found was that though the chicks did not know what to expect when confronted with identical numbered squares, then tended to veer to the left when they saw lower numbers and veer right when the numbers were larger.
"A number is not either small or large in an absolute sense, but rather it is smaller or larger with respect to another number" lead author of the study, Rugani says. "The [chicks] associate small numbers with the left space and larger number with the right space, and this resembles the humans' behavior in responding to numbers."
Sensing the relative sizes of the numbers, in comparison to the original target card, the chicks displayed an ability for advanced cognition and reasoning skills suggesting their ability to visualize a "mental number line" (MNL). Used commonly by humans, these MNL quantify numbers based on ascending order from smallest (on the left) to the largest (on the right). And with this ability engrained in the chicks, researchers now believe that the habit of visualizing numbers on these number lines evolved millions of years ago, before the ancestor of humans and modern-day birds diverged.
Want to see these chicks in action? Check out the video below to see how Rigani and her colleagues were able to coax the tiny chicks into crunching the numbers in their heads, and how they sorted out their treats from the numbered tricks.
The study published this week adds to the growing literature on spatial strategies, and while continued research will be necessary to further determine which creatures have this ability, and when it was potentially derived in our vast evolutionary tree, researchers now believe that these chicks have given us a place in our history to start the hunt. And soon other species divergent from humans at a later branch in the evolutionary tree will be tested, as well Rugani says.
"Our results indicate that a disposition to map numerical magnitudes onto a left-to-right oriented MNL exists independently of cultural factors and can be observed in animals with very little non-symbolic numerical experience" Rugani says. "[In fact], spatial mapping of numbers from left to right may be a universal cognitive strategy available soon after birth."
