Paleoenvironmental basis of cognitive evolution in great apes

Abstract

A bias favoring tree-dominated habitats and ripe-fruit frugivory has persisted in great ape evolution since the early Miocene. This bias is indicated by fossil ape paleoenvironments, molar morphology, dental microwear, the geographic pattern of extinctions, and extant apes' reliance on wooded settings. The ephemeral aspect of high-quality fruit has placed a premium on cognitive and social means of finding and defending food sources, and appears related to great apes' affinity since the Miocene for wooded, fruit-rich environments. These habitats have, however, undergone a severe withdrawal toward the low latitudes of Africa and Southeast Asia since the late Miocene, corresponding to a decline in the diversity of great apes beginning 9.5 million years ago. Plio-Pleistocene records imply that wooded settings of Africa and SE Asia were prone to substantial fragmentation and coalescence. Once apes were confined to equatorial settings, therefore, habitat instability heightened the spatial/temporal uncertainty of ripe-fruit sources. Prolonged learning, the assignment of attributes to distant places, mental representation, and reliance on fallback foods were all favored in this dynamic environmental context. These abilities helped sustain forest frugivory in most lineages. Fluid social grouping afforded the animals opportunities to locate ephemeral foods in continuous and fragmented forests. Fission-fusion grouping also magnified the problems of object impermanence (of individuals) and dispersion manifested by food sources in the ecological realm. Thus the spatial and temporal dynamics of fruit and wooded habitats since the Miocene are reflected in important components of great ape cognition, foraging, and sociality. In contrast to great apes, cercopithecoid monkeys have increased their plant dietary options and diversified in seasonal environments since the late Miocene. Early hominins eventually severed the habitat bias that characterized the evolution of great apes, and later expanded into diverse environments.

Wild chimpanzees plan their breakfast time, type, and location

“…We propose that large-brained foragers that need a reliable and steady intake of high-energy nutrition to maintain their large and costly brains (6,11) could gain a clear evolutionary advantage by using flexible planning that reduces indirect interspecific competition. This attribute may have been particularly important for hominoids that specialized on stationary, energy-rich, and highly ephemeral food, such as ripe fruit (14,17,24), abandoned meat carcasses, or aquatic fauna trapped in receding waters (56). The proposed benefit of flexible planning skills, especially for hominids living in highly seasonal habitats like savannah, strongly encourages a more detailed focus on the temporal aspect of ecological complexity than has been done to date (1,6), and a resumed investigation of its role in theories of primate and, in particular, hominid brain size evolution (11).…”

“…We investigated whether a ripe-fruit specialist, the chimpanzee (24), uses prospective cognition to arrive earlier at breakfast sites with ephemeral and highly sought-after fruits (in particular figs and small fruits) than those with less ephemeral fruit that can be more predictably obtained throughout the entire day. To accomplish this, we recorded and analyzed (i) the nest (sleeping site) departure times and (ii) nest positioning relative to breakfast-site locations of five adult female chimpanzee all with young offspring (<7 y) during three fruit-scarce periods in the Taï National Park, Ivory Coast (25,26).…”

Cognitive adaptations of social bonding in birds

“…These traits tended to be found in those birds with a large relatively sized brain, an omnivorous diet, a complex social system and which live in a harsh, changeable environment: traits which are shared with mammals that have been suggested to be the most intelligent. Indeed, Godfrey-Smith (1996), Sterelny (2003) and Potts (2004) have suggested that such environmental complexity presented numerous ecological problems for our hominid ancestors which could only be solved by the evolution of flexible forms of innovative behaviour.…”

A socioecological perspective on primate cognition, past and present

“…For example, Byrne (1999) suggests that ape planning and cultural learning abilities allow apes to gain access to novel foods. Potts (2004) proposes that habitat instability about 9.5 mya increased the diYculty of surviving on a ripe fruit diet and selected for cognitive and social means of Wnding food and is responsible for the higher intelligence of apes.…”