Humans and fuzzy newborn chicks have something in common—we tend to imagine numbers increasing from left to right. Although chicks can’t count in the same sense that humans can, they can distinguish between smaller and larger numbers of objects. Now, scientists have shown that chicks favor smaller numbers on the left and larger numbers on the right by noting how they choose between two cards with squares printed on them. Scientists trained the chicks by familiarizing them with a card with five squares and tempting them with a delicious mealworm hidden behind it. Later, when presented with a pair of identical cards, each with two squares—a smaller number than they had been trained with—the chicks usually searched for food behind the one on the left. When the test was repeated with two cards showing eight squares, they favored the card on the right, the team reports online today in Science. The similarity between chicks and humans suggests that humans’ “mental number line” is likewise innate, yet there is still a cultural component, as the left-right tendency can vary based upon language. Arabic speakers, who write from right to left, may have the opposite orientation, for example. The researchers suggest that the preferred direction of the number line could originate in brain asymmetries that are common to birds and humans. So your mental number map may be the result of being a birdbrain.