Numerosity is informative for living organisms. It cantransmit, among many things, amount of food available,heading direction of the troop, which group could win aterritorial dispute, the decision of were to build a beehive.Given its ecological importance, we test the hypothesisthat numerosity captures visual selection. In five exper-iments we confirmed that an irrelevant visual stimulusthat was numerically large slowed down participants indetecting a task-relevant visual target (Exp. 1 and 2). Thiscapture was not driven by sensory variables that could cor-relate with numerosity: cumulative area (Exp. 3) and ele-ment size (Exp. 4). We also confirmed that the underlyingnumerosity representations were analogue, not set-based(Exp. 5). In a crowded visual scene numerosity is a rele-vant cue for visual selection, but represented only in ap-proximate/coarse fashion.

Probabilities can be described by a numerator and a de-nominator and students and decision-makers are not in-different to numerical values of the components. For in-stance, when people compare two equal ratios their choicesgravitate to the option with larger number, even if theyknow both ratios are equal. To the date, however, it is un-clear if whole number biases are present in other cultures.We tested a farming-foraging group living in the Bolivianrain forest in a simple 2AFC ratio comparison task. Af-ter appropriate training, the Tsimane were highly accu-rate in this task, confirming that visual proportional rea-soning is present across cultures. Importantly, they hada strong tendency to favor large numbers in equal ratiocomparisons, similar to what is found in educated popu-lations. Even though our sample size is moderate (n=76),the whole number bias we found occurred under good pro-portional reasoning. The bias may be a general feature ofcognition, rather than a cultural or education artifact, thatmay help humans solve ambiguous situations.

We study the projection of cognitive representations into continuous motor (reaching) responses with a computational model that unifies three influential approaches: accumulation of evidence, statistical inference, and optimal feedback control. We modeled a number comparison task that asked participants to respond with a reaching gesture which of two side had more dots. The model successfully reproduced subjects’ pattern of reach and performance across varying difficulties of numerical comparison. Our model parameterized several potentially relevant cognitive variables, including a threshold, memory decay, and mental sampling rate. Remarkably, a threshold for movement was not needed for modeling human behavior when statistical inference is combined with optimal motor planning. Overall, the model indicates that the motorsystem positions the effectors optimally, both biomechanically through an optimal feedback controller, and cognitively by means of continuous statistical inference on the available evidence.

Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.