Opinion – Marcelo Viana: Bees can distinguish odd and even numbers

In an article published in the scientific journal Frontiers in Ecology and Evolution, in April of this year, Australian researchers describe a surprising discovery: honey bees are able to distinguish odd and even numbers. It is not the first report of numerical abilities in animals. But it is disconcerting, because the notion of parity is quite abstract and, in the case of humanity, it seems to be linked to certain complex functions of the brain.

We know that young children tend to associate evens with “right” and odds with “left.” Other studies show that we react more quickly to even numbers with our right hand and odd numbers with our left hand. It is not clear what evolutionary factor would have generated such associations, nor what would have led a species as simple as the bee to develop this type of capacity.

The researchers divided the bees into two groups. The first was presented with cards with different numbers —from one to ten— of objects drawn, soaked in water with sugar, if the number of objects was even, or water with quinine (bitter), otherwise. The second group was trained to associate the evens with bitter water and the odds with sweetened water, using the same idea in reverse.

Bees are great students: in a short time they were already correct more than 80% of the time in choosing sweetened cards. Even more impressive, when the scientists switched to cards with more objects drawn (11 or 12), which had not been used in training, the accuracy of the insects remained above 70%.

A mysterious fact is that bees seem to prefer odd numbers: the second group, which associated odd numbers with sweetened water, learned more quickly than the first. Furthermore, in both groups, the learning of odd numbers was faster than that of even numbers. Among human children, it is usually the other way around.

Until then, it was believed that the ability to distinguish even from odd required a complex brain, like the human, which has about 86 billion neurons. The bee’s brain, with a mere 960,000 neurons, didn’t seem to be up to the task. From the discovery, the researchers devised a small “artificial brain”, a neural network with only 5 neurons, and verified that it was capable of learning to distinguish the parity of numbers, with precision of up to 100%. But it’s not clear whether bees and neural networks learn in the same way.