No clear evidence for an innate left-to-right mental number line

The origins of number sense: a commentary on "Is there an innate sense of number in the brain?"

The question of whether a "sense of number" is innate has been posed in a new article by Lorenzi et al. (2025). The article explores the behavioral and neurobiological evidence from newborn animals to delve into the evolutionary origins of a sense of number. Lorenzi et al.(2025) raises new questions, interpretations, and ideas for future work to understand how number sense has evolved in humans and nonhuman animals. In this commentary, I discuss the arguments for an innate number sense, evaluate the implications for numerical cognition, and suggest how future work could fill the current gaps in our knowledge.

Quantity misperception by hymenopteran insects observing the solitaire illusion

Visual illusions are errors in signal perception and inform us about the visual and cognitive processes of different animals. Invertebrates are relatively less studied for their illusionary perception, despite the insight that comparative data provides on the evolution of common perceptual mechanisms. The Solitaire Illusion is a numerosity illusion where a viewer typically misperceives the relative quantities of two items of different colors consisting of identical quantity, with more centrally clustered items appearing more numerous. We trained European honeybees (Apis mellifera) and European wasps (Vespula vulgaris) to select stimuli containing a higher quantity of yellow dots in arrays of blue and yellow dots and then presented them with the Solitaire Illusion. Insects learnt to discriminate between dot quantities and showed evidence of perceiving the Solitaire Illusion. Further work should determine whether the illusion is caused by numerical cues only or by both quantity and non-numerical spatial cues.