For over a century, various neuroanatomical measures have been employed as assays of cognitive ability in comparative studies. Nevertheless, it is still unclear whether these measures actually correspond to cognitive ability. A recent meta-analysis of cognitive performance of a broad set of primate species has made it possible to provide a quantitative estimate of general cognitive ability across primates. We find that this estimate is not strongly correlated with neuroanatomical measures that statistically control for a possible effect of body size, such as encephalization quotient or brain size residuals. Instead, absolute brain size measures were the best predictors of primate cognitive ability. Moreover, there was no indication that neocortex-based measures were superior to measures based on the whole brain. The results of previous comparative studies on the evolution of intelligence must be reviewed with this conclusion in mind.

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Geographic variation in socially transmitted skills and signals, similar to human culture, has been well documented for great apes. The rules governing the adoption of novel behaviours, however, are still largely unknown. We conducted an innovation-and-transmission experiment with two groups of chimpanzees living at hopE Primate Sanctuary Gänserndorf, Austria, presenting a board on which food had to be manoeuvred around obstacles to be acquired. Most chimpanzees used sticks to acquire the food, but Wve adults independently invented a novel technique, rattling, which was subsequently tested by almost all group members. However, individuals who had become proWcient with sticks were reluctant to switch to rattling, despite it being more eYcient. Similarly, after rattling was prevented, rattle specialists kept trying to rattle and made no attempt to use the stick technique, despite their knowledge about its existence. We conclude that innovators stimulate others to experiment with the solutions they display, but that chimpanzees are nevertheless conservative; mastery of a skill inhibits further exploration, and hence adoption of alternative techniques even if these are more eYcient. Consequently, conformity among group members should not be expected in great apes when individuals develop proWciency at diVerent techniques. Conservatism thus joins conformity as a mechanism to bring about cultural uniformity and stability.

The explanation of patterns in species richness ranks among the most important tasks of ecology. Current theories emphasize the interaction between historical and geographical factors affecting the size of the regional species pool and of locally acting processes such as competitive exclusion, disturbance, productivity, and seasonality. Local species richness, or alpha diversity, of plants and primary consumers has been claimed to peak in habitats of low and intermediate productivity, which, if true, has major implications for conservation. Here, by contrast, we show that local richness of Neotropical primates (platyrrhines) is inf luenced by both historical biogeography and productivity but not by tree species richness or seasonality. This pattern indicates that habitats with the highest plant productivity are also the richest for many important primary consumers. We show further that fragmentation of Amazonian rain forests in the Pleistocene, if it occurred, appears to have had a negligible inf luence on primate alpha species richness.Patterns of local animal species richness have been suggested to be causally related to tree species richness, plant productivity, seasonality, habitat heterogeneity, and historical͞ geographical factors (1-5). However, because there are very few sites for which all variables have been measured, the independent effect of these possible causal factors has so far not been assessed. Here, we circumvent this problem by examining the correlations of these variables with an intermediate variable, local rainfall.Previous studies from various tropical regions reported a monotonic increase in richness with rainfall (6-9). However, these studies sampled very few sites with annual rainfall of over 2500 mm and͞or analyzed the relationship using linear regression and were therefore unable to test more complex hypotheses of relationship. We have gathered new data for Neotropical primate richness through a broader range of rainfall levels. Fig.