Mathematical abilities in adult humans exceed the numerical capacities of any non-human animal. Although neither rat nor monkey is likely to balance a checkbook or prove Pythagorous' theorem there is considerable evidence that non-human animals are capable of impressive mathematical feats in their own right. Animal genera as diverse as rats, pigeons, ferrets, raccoons, monkeys, and apes have been shown to make numerical judgments with stimuli that include light flashes, tones, abstract visual elements, house-hold objects, food morsels, and their own responses (for reviews see Boysen &Capaldi, 1992;Brannon &Roitman 2003;Gallistel &Gelman, 1992;Dehaene, 1997). The PI's previous research has contributed to this literature by demonstrating that rhesus monkeys represent abstract ordinal relations between numerosities and that pigeons represent number on a linear rather than a logarithmic scale. Furthermore, a growing body of data suggests that the nonverbal numerical system, held by animals, is shared by humans and appears early in development (e.g., Brannon, 2002;Brannon &Terrace, 2002;Whalen et al., 1999;Spelke, 2000). Studying the evolutionary basis of human numerical capacities will provide important insight into the nature of this system. Three main gaps remain in our knowledge of non-verbal numerical cognition in animals, 1) whether numerical representations are abstract or concrete, 2) the role of learning in the expression of particular numerical abilities, and 3) which aspects of human numerical cognition are phylogenetically conservative and which aspects are shared by some or all primates. The results of the proposed experiments will provide a more complete understanding of non-verbal numerical cognition and provide a springboard for understanding the evolutionary bases of human numerical cognition. Furthermore the proposed research seeks to provide a monkey model that will provide insight into normal numerical development in children and a basis for understanding atypical development. As such this research will contribute to the PIs broad goal of understanding the relationship between mathematical thinking in animals and human infants in an effort to shed light on thought without language and the building blocks of adult human cognition.