Honeybees, like many people, prefer to have their numbers arranged from left to right.
A new study has shown that honeybees who are trained to recognize a particular number fly left when presented with two options. They also fly right when they are offered a larger number. These findings suggest that honeybees have a “mental number line”This association is biologically rooted, researchers report on October 17 in the Proceedings of the National Academy of Sciences.
Some scientists are in agreement that the study supports a mental number line for honeybees. Others argue that it simplifies complex human behavior.
Many humans have a mental number line that often puts smaller numbers on the left and bigger numbers on the right — if asked to organize several bunches of grapes by size, you’d likely line them up by increasing number of grapes from left to right. This question has been debated for years about whether this association is learned later in life or if it is present at birth.
The results of previous work have shown this. Honeybees can countThey even get it! The concept of zero (SN: 6/7/18). “When you realize all these facts, an obvious question [is whether honeybees have] the so-called mental number line,” says Martin Giurfa, a biologist at the Université Paul Sabatier in Toulouse, France. Giurfa tested the honeybees of 134 colonies from his home during COVID-19 lockdowns.Apis mellifera) on their number-ordering abilities using a design developed with researchers who had done Similar experiments were conducted with chicks human babies (SN: 1/29/15).
Giurfa needed to first teach his bees to recognize numbers. He used sugar water to lure honeybees into testing chambers made of a repurposed bottle box. For each bee, he hung a panel on the back of the box with a certain number of symbols on it — one, three or five — and fed them the sugar water so they’d learn to associate the number with food. He changed the symbols between visits so that they were learning the number and not certain shapes.
After 30 trips to this box, Giurfa decided it was time to test. He removed the training panel from the box and installed two mirror-image panels on the right and left walls. These panels had either the same number of symbols, or fewer symbols.
Which panel did the bees fly to — left or right? “It depends on your reference number,” Giurfa says. Of the bees trained on “one,” 72 percent flew to the “three” panel to the right, but of the bees trained on “five,” 73 percent went to the “three” panel to the left. “That’s exactly the concept of the mental number line,” Giurfa says. “You align numbers based on your reference.” If the test number was the same as the training number, the bees showed no preference for left or right.
These experiments “make a very compelling case” for a mental number line in honeybees, says Felicity Muth, a biologist at the University of Texas at Austin who was not involved with the study. “They have a number of controls that really rule out any of the alternative explanations I can think of.”
Giurfa believes these results demonstrate that mental number lines (or at least a component thereof) are present throughout the animal kingdom. But not all are convinced.
“The oversimplification of complex human concepts, such as that of ‘number line,’ must be avoided, since they severely distort the reality of the phenomena that make them possible,” says Rafael Núñez, a cognitive scientist at the University of California, San Diego.
Núñez, who coauthored A critical article about the earlier chick studyShe believes animal research should examine why bees, chicks, and other human groups have different mental number lines. those he’s studied in Papua New Guinea, don’t. Giurfa recognizes the role culture plays in explaining why Every adult is not able to order numbers from left and right.However, he feels that there is evidence for a biological underpinning.SN: 8/23/21).
This study stops short of explaining why the brains of bees, chicks and babies have all converged on the same left-to-right number ordering but does offer a possible answer — their asymmetrical brains. All three species have brains that process information differently from the right and left sides. “It might be an inherent property to these lateralized brain systems,” Giurfa says.
A common system of organizing numbers would, if it were to be widespread, show how similar our animal minds can seem to ours. Giurfa believes that while some cognitive abilities seem unique to humans, it is dangerous to dismiss the abilities of animals. “We are different from animals in some aspects,” he says, “but we are very similar in others. Denying this similarity is not what will help us understand what we are.”
