Human universals and primate symplesiomorphies: Establishing the lemur baseline

Abstract

Social behavior, culture, and cognition are domains where presumably most human universals exist. Identification of these derived human traits depends and relies on comparisons with other primates, notably chimpanzees. This approach can also be used to reconstruct primate and human behavioral evolution. Accordingly, traits found in both Homo and Pan can be inferred to have existed in their last common ancestor as well. By analogy, traits shared between humans and other primates can be traced back even further down on our family tree. Here, we look at the other side of human universals, i.e., behavioral and cognitive traits of the most basal living primates, which ought to represent the common primate legacy upon which later taxon-specific specializations were built. Specifically, we review studies investigating cognitive abilities and social behavior of the lemuriform primates of Madagascar. The Malagasy lemurs are particularly important for this purpose because they alone, among strepsirrhine primates, have evolved group-living, which characterizes most living haplorrhines. Even though lemurs have relatively smaller brains than New and Old World monkeys and great apes, their ability to solve problems that require technical intelligence is qualitatively on par with that of haplorrhines. In the domain of social intelligence, however, lemurs deviate from the better-known haplorrhine models (i.e., cercopithecines) in several respects. Most importantly, their behavioral strategies reflect an emphasis on within-group competition, rather than cooperation, which may represent lemur-specific adaptations to an ecologically unpredictable environment, rather than fundamental deficits in social intelligence. In any event, a broad comparative perspective including the best living models of the earliest gregarious primates can enrich reconstructions and other evolutionary analyzes of primate social behavior, including that of humans.