Biology subjects

van Schaik, C. P.

Publications and source records attributed to van Schaik, C. P..

3 recordsLinked to original sources

bioRxiv2021

A farewell to EQ: A new brain size measure for comparative primate cognition

Both absolute and relative brain size vary greatly among and within the major vertebrate lineages. Scientists have long debated how larger brains in primates and hominins translate into greater cognitive performance, and in particular how to control for the relationship between the non-cognitive functions of the brain and body size. One solution to this problem is to establish the slope of cognitive equivalence, that is the line connecting organisms with an identical bauplan but different body sizes. Here, we suggest that intraspecific slopes provide the best available estimate of this measure. This approach was abandoned because slopes were too low by an unknown margin due to estimation error. We control for the error problem by focusing on highly dimorphic primate species with large sample sizes and fitting a line through the mean values for adult females and males. We obtain the best estimate for the slope of ca 0.27, a value much lower than those constructed using all mammal species, and close to the value expected based on the genetic correlation between brain size and body size. We also find that the estimate of cognitive brain size based on cognitive equivalence fits empirical cognitive studies better than the encephalization quotient (EQ), which should therefore be avoided in future studies on primates, and presumably mammals and birds in general. The use of residuals from the line of cognitive equivalence may change conclusions concerning the cognitive abilities of extant and extinct primate species, including hominins.

animal behavior and cognition↗

bioRxiv2021

Wild-captive contrasts in non-vocal communicative repertoires and functional specificity in orang-utans

The creation of novel communicative acts is an essential element of human language. Although some research suggests the presence of this ability in great apes, this claim remains controversial. Here, we use orang-utans (Pongo spp.) to systematically assess the effect of the wild-captive contrast on the repertoire size of communicative acts. We find that individual communicative repertoires are significantly larger in captive compared to wild settings, irrespective of species, age-sex class or sampling effort. Twenty percent of the orang-utan repertoire in captivity were not observed in the wild. In Sumatran orang-utans, the more sociable species, functional specificity was also higher in captive versus wild settings. We thus conclude that orang-utans, when exposed to a more sociable and terrestrial lifestyle, have the behavioural plasticity to invent new communicative behaviours that are highly functionally specific. This productive capacity by great apes is a major prerequisite for the evolution of language and seems to be ancestral in the hominid lineage.

animal behavior and cognition↗

bioRxiv2019

The nose is mightier than the tooth: larger male proboscis monkeys have smaller canines

The uniquely enlarged noses of male proboscis monkeys are prominent adornments, and a sexually selected male trait. A recent study showed significant correlations among nose, body, and testis sizes and clear associations between nose size and the number of females in a males harem. However, to date, the analyses of other common male traits, i.e., canines, are lacking. Whereas male nose size had a positive correlation with body size, we unexpectedly found a negative correlation between body and canine sizes. We explain this by an interaction between sexual and natural selection. Larger noses in males may interfere with the use of canines, thereby reducing their effectiveness as weapons. Additionally, longer canines are opposed by natural selection because the larger gape it imposes upon its bearer reduces foraging efficiency, particularly in folivores. This unique case of decoupling of body and canine size reveals that large canines carry an ecological cost.

evolutionary biology↗