Early Pleistocene faunivorous hominins were not kleptoparasitic, and this impacted the evolution of human anatomy and socio-ecology

Humans are unique in their diet, physiology and socio-reproductive behavior compared to other primates. They are also unique in the ubiquitous adaptation to all biomes and habitats. From an evolutionary perspective, these trends seem to have started about two million years ago, coinciding with the emergence of encephalization, the reduction of the dental apparatus, the adoption of a fully terrestrial lifestyle, resulting in the emergence of the modern anatomical bauplan, the focalization of certain activities in the landscape, the use of stone tools, and the exit from Africa. It is in this period that clear taphonomic evidence of a switch in diet with respect to Pliocene hominins occurred, with the adoption of carnivory. Until now, the degree of carnivorism in early humans remained controversial. A persistent hypothesis is that hominins acquired meat irregularly (potentially as fallback food) and opportunistically through klepto-foraging. Here, we test this hypothesis and show, in contrast, that the butchery practices of early Pleistocene hominins (unveiled through systematic study of the patterning and intensity of cut marks on their prey) could not have resulted from having frequent secondary access to carcasses. We provide evidence of hominin primary access to animal resources and emphasize the role that meat played in their diets, their ecology and their anatomical evolution, ultimately resulting in the ecologically unrestricted terrestrial adaptation of our species. This has major implications to the evolution of human physiology and potentially for the evolution of the human brain.

Sustainable Peeling of Kapok Tree (Ceiba pentandra) Bark by the Chimpanzees (Pan troglodytes verus) of Comoé National Park, Ivory Coast

Primates often consume either bark or cambium (inner bark) as a fallback food to complete their diet during periods of food scarcity. Wild chimpanzees exhibit great behavioral diversity across Africa, as studies of new populations frequently reveal. Since 2014, we have been using a combination of camera traps and indirect signs to study the ecology and behavior of wild chimpanzees (Pan troglodytes verus) in Comoé National Park, Ivory Coast, to document and understand the behavioral adaptations that help them to survive in a savanna–forest mosaic landscape. We found that Comoé chimpanzees peel the bark of the buttresses of kapok tree (Ceiba pentandra) trees to eat the cambium underneath. Individuals of all sex/age classes across at least six neighboring communities peeled the bark, but only during the late rainy season and beginning of the dry season, when cambium may represent an important fallback food. Baboons (Papio anubis) also target the same trees but mainly eat the bark itself. Most of the bark-peeling wounds on Ceiba trees healed completely within 2 years, seemingly without any permanent damage. We recorded chimpanzees visiting trees in early stages of wound recovery but leaving them unpeeled. Only 6% of peeled trees (N = 53) were reexploited after a year, suggesting that chimpanzees waited for the rest of the trees to regrow the bark fully before peeling them again, thus using them sustainably. Many human groups of hunter-gatherers and herders exploited cambium sustainably in the past. The observation that similar sustainable bark-peeling behavior evolved in both chimpanzees and humans suggests that it has an important adaptive value in harsh environments when other food sources become seasonally scarce, by avoiding the depletion of the resource and keeping it available for periods of scarcity.

Hominoid Adaptation to Dietary Ethanol

Humans’ long association with alcohol raises questions about both our biological adaptations to handling ethanol and its origins. Fermented foods have less sugar, and require additional detoxification than unfermented versions of the same food, and are thus are generally inferior food choices. I summarize recent studies which indicate that our ability to exploit ethanol depends on several mutations in alcohol dehydrogenase (ADH) enzymes that allow ethanol to be metabolized rapidly, thereby reducing the likelihood that the blood alcohol concentration reaches intoxicating levels. Genetic and biochemical analyses for a wide range of primate and non-primate species suggest that these mutations are shared primarily with the two African great apes (chimpanzees and gorillas). These mutations thus date back at least 10 million years, to a period when the tropical forests were contracting during a major episode of climate change. Mutations enabling rapid ethanol metabolism may have enabled ancestral apes to exploit otherwise toxic, ethanol-rich fermenting fruits on the forest floor that were metabolically inaccessible to their ecological competitors. These adaptations enabling exploitation of an inferior food suggest that modern proclivities towards ethanol consumption may derive from the utilization of fermented food as a particular type of fallback food. If so, the fermented fallback food hypothesis can be seen as a special case of the drunken monkey hypothesis.

Impact of Snow Storms on Habitat and Death of Yunnan Snub-Nosed Monkeys in the Baimaxueshan Nature Reserve, Yunnan, China

Natural disasters such as snow storms have far-reaching effects on variations in the habitat structure and ecological aspects of non-human primates. Yunnan snub-nosed monkeys (Rhinopithecus bieti) inhabit high-altitude forest and endure harsh winters. The effect of heavy snow-storms (January 19 to February 6, 2008) on two large groups of R. bieti (Gehuaqing group and Xiangguqing group) inhabiting Samage Forest in the Baimaxueshan Nature Reserve were assessed. Data on habitat damage were collected between March and May 2008 via field line sampling. The snow storms destroyed 237 big trees in the Samage Forest. The destroyed trees were mostly located along the mountain ridge and valley including Abies georgei, Tsuga dumosa, Pinus yunnanensis and Cyclobalanopsis oxyodon. These trees were important for R. bieti as they provide a dietary source of lichen that is a critical winter fallback food for this primate species, and consequently food availability for R. bieti was reduced. Our results also showed that two juveniles in the Gehuaqing group and three juveniles in the Xiangguqing group were found deceased following the storms. The fact indicates that R. bieti is well adapted to high altitude and strongly seasonal habitat might explain its resilience to heavy snow storms.