Confrontational Scavenging Research Articles

Computer simulation of scavenging by hominins and giant hyenas in the late Early Pleistocene

Consumption of animal-sourced food is an important factor in broadening the diet of early hominins, promoting brain and body growth, and increasing behavioural complexity. However, whether early hominins obtained animal food by scavenging or hunting large mammals remains debated. Sabre-toothed felids have been proposed to facilitate the expansion of early Homo out of Africa into Europe 1.4–0.8 Ma by creating a niche for scavengers in Eurasia as the carcasses abandoned by these felids still contained abundant edible resources. In contrast, it has been argued that the niche for a large scavenger was already occupied in Eurasia by the giant hyena, preventing hominins from utilising this resource. This study shows that sabre-toothed felids generated carcasses rich in edible resources and that hominins were capable of competing with giant hyenas for this resource. The simulation experiments showed that maintaining an optimum group size is essential for the success of the hominin scavenging strategy. Early hominins could outcompete giant hyenas only if they could successfully dispute carcasses with them. Thus, in the presence of a strong competitor, passive scavenging is essentially the same as confrontational scavenging.

Evolutionary ecology of language origins through confrontational scavenging.

A dynamic model and an agent-based simulation model implementing the assumptions of the confrontational scavenging hypothesis on early protolanguage as an adaptive response of Homo erectus to gradual change in their habitat has been developed and studied. The core assumptions of the hypothesis and the model scenario are the pre-adaptation of our ancestors to occupy the ecological niche that they constructed for themselves by having evolved displaced communication and a rudimentary tool manufacture, two features allowing them to use a new, concentrated and abundant resource-megafauna carrion-on the savannahs replacing arboreal habitats owing to the drying climate of East Africaat about 2Ma. The shift in diet required coordinated cooperation by the hominin scavengers confronted with concurrent predators. Power scavenging compelled displaced symbolic communication featuring a limited semantic range; syntax was not yet required. We show that phenotypic evolution on the accuracy of information transfer between cooperating hominins is a necessary and sufficient condition for the population of agents to survive the diet shift. Both the individual and the group fitness of the hominin horde increased with the accuracy of their protolanguage, with decreasing time allocated to foraging and thus more time left for culture. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Wild chimpanzees deprived a leopard of its kill: Implications for the origin of hominin confrontational scavenging

This study reports the first observed case of wild chimpanzees (Pan troglodytes) obtaining animal prey freshly killed by a sympatric leopard (Panthera pardus) and scavenging it with the leopard still nearby. This observation has important implications for the emergence of confrontational scavenging, which may have played a significant role in human evolution. Many scholars agree that eating meat became important during human evolution, and hominins first obtained meat by scavenging. However, it is debatable whether scavenging behavior was “passive” or “confrontational (power).” The latter is more dangerous, as it requires facing the original predator, and it is thus considered to have been important for the evolution of several human traits, including cooperation and language. Chimpanzees do scavenge meat, although rarely, but no previous evidence of confrontational scavenging has hitherto emerged. Thus, it was assumed that they are averse to confrontation with even leopard-sized predators. However, in the observed case the chimpanzees frequently emitted waa barks, which indicated that they were aware of the leopard's presence but they nevertheless continued to eat the scavenged meat. In addition, we compiled and reviewed 49 cases of chimpanzee encounters with animal carcasses in the Mahale Mountains of Tanzania in 1980–2017. Chimpanzees scavenged meat in 36.7% of these cases, and tended to eat the meat when it was fresh or if the animal species was usually hunted by chimpanzees. However, no evidence indicated that carcasses were avoided when leopard involvement was likely. These results suggest that chimpanzee-sized hominins could potentially confront and deprive leopard-size carnivores of meat.

The social organization of Homo ergaster: Inferences from anti-predator responses in extant primates

Patterns of primate socioecology have been used to suggest that the first truly savanna-dwelling hominin, Homo ergaster, lived in sizeable groups. Here, we revisit these estimates and infer additional features of the social organization of these early hominins based on anti-predator responses observed across the primate taxon. We first show that the effect of habitat on primate group size, composition, and sexual dimorphism is negligible after controlling for substrate use and phylogeny: terrestrial species live in larger groups with more and bigger males than arboreal taxa. We next hypothesize that groups can only survive in open habitats if males are able to engage in joint counter-attacks against the large carnivorans typical of such environments. To test this, we analyze reports on primate counter-attacks against known predators and find these are indeed disproportionately frequent in terrestrial taxa living in open habitats, sometimes even involving the use of tentative weapons. If we subsequently only examine the taxa that are particularly adept at this (chimpanzees and baboons), we find an effect of habitat type on group size: groups on the savanna are larger than those in the forest. We thus infer that H. ergaster lived in very large groups with many males that jointly defended the group against carnivorans, and argue that these counter-attacks will readily have turned into confrontational scavenging and cooperative hunting, allowing Homo to move into the niche of social carnivore. These two features (life in very large multi-male groups and a switch to persistent carnivory) shaped the evolution of our lineage to such an extent that the social organization of H. ergaster may already have contained many key elements characterizing modern day foragers: male bonding, incipient male–female friendships with food sharing, a tendency toward endogamy, and the presence of large communities that eventually turned into the ethno-linguistic units we can still recognize today.

In the beginning: A review of Robert C. Berwick and Noam Chomsky's Why Only Us.

We review Berwick and Chomsky's Why Only Us, Language and Evolution, a book premised on language as an instrument primarily of thought, only secondarily of communication. The authors conclude that a Universal Grammar can be reduced to three biologically isolated components, whose computational system for syntax was the result of a single mutation that occurred about 80,000 years ago. We question that argument because it ignores the origin of words, even though Berwick and Chomsky acknowledge that words evolved before grammar. It also fails to explain what evolutionary problem language uniquely solved (Wallace's question). To answer that question, we review recent discoveries about the ontogeny and phylogeny of words. Ontogenetically, two modes of nonverbal relation between infant and mother begin at or within 6 months of birth that are crucial antecedents of the infant's first words: intersubjectivity and joint attention. Intersubjectivity refers to rhythmic shared affect between infant and caretaker(s) that develop during the first 6 months. When the infant begins to crawl, they begin to attend jointly to environmental objects. Phylogenetically, Hrdy and Bickerton describe aspects of Homo erectus' ecology and cognition that facilitated the evolution of words. Hrdy shows how cooperative breeding established trust between infant and caretakers, laying the groundwork for a community of mutual trust among adults. Bickerton shows how 'confrontational scavenging' led to displaced reference, whereby an individual communicated the nature of a dead animal and its location to members of the group that could not see it. Thus, both phylogenetically and ontogenetically, the original function of language was primarily an instrument of communication. Rejecting Berwick and Chomsky's answer to Wallace's question that syntax afforded better planning and inference, we endorse Bickerton's view that language enabled speakers to refer to objects not immediately present. Thus arose context-free mental representations, unique to human language and thought.

Humans and Scavengers: The Evolution of Interactions and Ecosystem Services

Since the origin of early Homo species during the Late Pliocene, interactions of humans with scavenging birds and mammals have changed in form through shifting ecological scenarios. How humans procured meat during the Quaternary Period changed from confrontational scavenging to hunting; shepherding of wild animals; and, eventually, intensive husbandry of domesticated animals. As humans evolved from carcass consumers to carcass providers, the overall relationship between humans and scavengers shifted from competition to facilitation. These changing interactions have translated into shifting provisioning (by signaling carcass location), regulating (e.g., by removing animal debris and controlling infectious diseases), and cultural ecosystem services (e.g., by favoring human language and social cooperation skills or, more recently, by enhancing ecotourism) provided by scavenging vertebrates. The continued survival of vultures and large mammalian scavengers alongside humans is now severely in jeopardy, threatening the loss of the numerous ecosystem services from which contemporary and future humans could benefit.

Confrontational scavenging as a possible source for language and cooperation

The emergence of language and the high degree of cooperation found among humans seems to require more than a straightforward enhancement of primate traits. Some triggering episode unique to human ancestors was likely necessary. Here it is argued that confrontational scavenging was such an episode. Arguments for and against an established confrontational scavenging niche are discussed, as well as the probable effects of such a niche on language and co-operation. Finally, several possible directions for future research are suggested.

Scavenging by chimpanzees at Ngogo and the relevance of chimpanzee scavenging to early hominin behavioral ecology

Chimpanzees regularly hunt a variety of prey species. However, they rarely scavenge, which distinguishes chimpanzee carnivory from that of some modern hunter-gatherers and, presumably, at least some Plio-Pleistocene hominins. I use observations made over an 11-year period to document all known opportunities for scavenging encountered by chimpanzees at Ngogo, Kibale National Park, Uganda, and describe all cases of scavenging. I also review data on scavenging from other chimpanzee research sites. Chimpanzees at Ngogo encountered scavenging opportunities only about once per 100 days and ate meat from scavenged carcasses only four times. Scavenging opportunities are also rare at other sites, even where leopards are present (Mahale, Taï, Gombe), and scavenging of leopard kills is known only from Mahale. Feeding on prey that chimpanzees had hunted but then abandoned is the most common form of scavenging reported across study sites. For example, several individuals at Ngogo ate meat from a partially consumed red colobus carcass abandoned after a hunt the previous day. Such behavior probably was not common among Oldowan hominins. Ngogo data and those from other sites also show that chimpanzees sometimes eat meat from carcasses of prey that they did not see killed and that were not killed by chimpanzees, and that scavenging allows access to carcasses larger than those of any prey items. However, chimpanzees ignore relatively many opportunities to obtain meat from such carcasses. Scavenging may be rare because fresh carcasses are rare, because the risk of bacterial infections and zoonoses is high, and because chimpanzees may not recognize certain species as potential prey or certain size classes of prey species as food sources. Its minimal nutritional importance, along with the absence of technology to facilitate confrontational scavenging and rapid carcass processing, apparently distinguishes chimpanzee foraging strategies from those of at least some Oldowan hominins.

Flaked stones and old bones: Biological and cultural evolution at the dawn of technology

The appearance of Oldowan sites ca. 2.6 million years ago (Ma) may reflect one of the most important adaptive shifts in human evolution. Stone artifact manufacture, large mammal butchery, and novel transport and discard behaviors led to the accumulation of the first recognized archaeological debris. The appearance of the Oldowan sites coincides with generally cooler, drier, and more variable climatic conditions across Africa, probably resulting in a net decrease in woodland foods and an increase in large mammal biomass compared to the early and middle Pliocene. Shifts in plant food resource availability may have provided the stimulus for incorporating new foods into the diet, including meat from scavenged carcasses butchered with stone tools. Oldowan artifact form varies with clast size, shape, raw material physical properties, and flaking intensity. Oldowan hominins preferred hard raw materials with good fracture characteristics. Habitual stone transport is evident from technological analysis, and raw material sourcing to date suggests that stone was rarely moved more than 2-3 km from source. Oldowan debris accumulation was spatially redundant, reflecting recurrent visitation of attractive points on the landscape. Thin archaeological horizons from Bed I Olduvai Gorge, Tanzania, were probably formed and buried in less than 10 years and document hominin processing of multiple carcasses per year. Transport beyond simple refuging behavior is suggested by faunal density at some site levels. By 2.0 Ma, hominin rank within the predatory guild may have been moderately high, as they probably accessed meaty carcasses through hunting and confrontational scavenging, and hominin-carnivore competition appears minimal at some sites. It is likely that both Homo habilis sensu stricto and early African H. erectus made Oldowan tools. H. habilis sensu stricto was more encephalized than Australopithecus and may foreshadow H. erectus in lower limb elongation and some thermoregulatory adaptations to hot, dry climatic conditions. H. erectus was large and wide-ranging, had a high total energy expenditure, and required a high-quality diet. Reconstruction of H. erectus reproductive energetics and socioeconomic organization suggests that reproductively active females received assistance from other group members. This inference, combined with archaeological evidence for acquisition of meaty carcasses, suggests that meat would have been a shared food. This is indirectly confirmed by nutritional analysis suggesting that the combination of meat and nutritionally dense plant foods was the likely diet fueling body size increase and encephelization in Homo. Most discussion of Oldowan hominin behavior and ecology, including that presented here, is based on materials from a few sites. There is a critical need to analyze additional large, primary-context lithic and faunal assemblages to better assess temporal, geographic, and environmental variability in Oldowan behavior.

Risk and opportunity for humans coexisting with large carnivores

Models of Plio-Pleistocene hominid behavioral ecology often emphasize competition with large carnivores. This paper describes competition between modern humans and large carnivores in rural Uganda, including active, confrontational scavenging of carnivore kills by humans and carnivore attacks on humans. Information gathered from Ugandan Game Department archives (1923–1994) reveals that twentieth-century agropastoralists regularly tried to scavenge from leopard (Panthera pardus) and lion (Panthera leo) kills, and that these large carnivores have preyed on hundreds of humans in Uganda over the past several decades. Men were most often targets of carnivore attack, particularly while engaged in hunting-related activities. However attacks on men were less often lethal than attacks on women and children. Analyses show that lion attacks were more dangerous than leopard attacks. These data support recent contentions that hominids armed with even simple weapons can succeed in active, confrontational scavenging by chasing carnivores from kills. Hominids sharing East African habitats with large carnivores may have been regularly subject to attack.

Mobility, competition, and Plio-Pleistocene hominid foraging groups

Evidence for carcass access times and levels of early hominid mobility is synthesized using studies of carnivore ethology and theories of interspecific competition to arrive at tentative conclusions about the organization of Plio-Pleistocene hominid foraging groups. The model presented suggests that group foraging tactics, in combination with high mobility, are central to successful confrontational scavenging (interference competition), whereas individual foraging tactics and high mobility are central to successful nonconfrontational scavenging (exploitative competition). In contrast, group or individual foraging tactics and low mobility characterize the acquisition of fresh carcasses in low-competition contexts. Individual foraging tactics and low mobility are employed in response to extreme competition over marginal resources. Preliminary tests with data from Bed I Olduvai Gorge and Koobi Fora suggest that Plio-Pleistocene hominids, like other large-bodied predators, employed flexible foraging tactics involving changes in group size and levels of mobility to gain access to carcasses in both low-and high-competition contexts.

Skeletal Inventories from Wildebeest Drownings at Lakes Masek and Ndutu in the Serengeti Ecosystem of Tanzania

Wildebeest drownings produce dense bone deposits over large surface areas adjacent to lakes and rivers in the Serengenti ecosystem of East Africa. Drownings occur during the annual wildebeest migration when animals cross rivers and lakes on their way to wet season pastures. Drownings involve both small and large numbers of adult and newborn wildebeest and can occur in a single event or a sequence of small and large events during the wet season. Signature criteria from surface skeletal remains produced by modern drownings that may, as an integrated set, help to identify them in the fossil record include: (1) the predominance of adults from a single species and the variable representation of newborns and yearlings; (2) the presence of intact elements from all adult skeletal groups; (3) assemblages dominated by axial elements and long bones; and (4) negative correlations between the representation of long bones and their marrow wet weights; assemblages from large drowning events possess weak negative correlations while small events possess strong negative correlations. The application of these criteria requires a landscape sampling strategy, because the drowning event's signature can be spread out over hundreds or thousands of metres of river or lake front. Consequently, localized samples from a large drowning may be affected differently by carnivores, flowing water, trampling, weathering, and/or burial and not possess all of these signature criteria. Drownings represent important scavenging opportunities for a wide variety of consumers because of the number of carcasses they can produce. Their occurrence in rivers and lakes also gives them some seasonal and spatial predictability. Under these circumstances, it is possible that water-restricted early hominids may have gained relatively early access to large animal carcasses without recourse to hunting or confrontational scavenging. Early access to carcasses would have been facilitated by the simultaneous presence of many drowned individuals over a large area, because these conditions act to reduce inter- and intra-specific competition for carcass foods among consumers. Later access to carcasses could still have provided hominids with a wealth of nutritious long bone marrow and cranial contents.

Hunting and Scavenging by Plio-Pleistocene Hominids: Nutritional Constraints, Archaeological Patterns, and Behavioural Implications

The subsistence activities and diet of ancient hominids are debated topics, and some researchers have recently questioned the view that meat was a significant dietary component of Plio-Pleistocene hominids. We examine the potential advantages and disadvantages of ungulate utilization by ancient hominids (e.g. Homo habilis and early Homo erectus) with regard to (a) human nutritional constraints, (b) seasonal variations in the physical condition of modern African ungulates, (c) the wild plant food potential of East African environments, and (d) the faunal record from Plio-Pleistocene sites such as FLK Zinjanthropus at Olduvai Gorge, Tanzania. The different lines of evidence suggest that the subsistence activities of early Homo probably included active, confrontational scavenging to obtain mostly intact carcasses of large animals and some opportunistic hunting of small animals, both of which yielded significant quantities of meat and fat that were an important source of calories, vitamins, and minerals. The possibility of consuming toxic amounts of protein could have been averted by emphasizing the consumption of organ meats and viscera at certain times of the year.

Sabertooth cats and their relevance for early hominid diet and evolution

Large carnivores structure the character of scavenging opportunities in any environment. In Pliocene and early Pleistocene Africa there were three large sabertooth cats sympatric with the ancestors of the modern felid community, and scavenging opportunities were presumably different from those in modern Africa. An understanding of a possible scavenging niche for early hominids must articulate knowledge gained from actualistic research with detailed reconstructions of extinct carnivore paleoecology. Contrasting skeletal and dental anatomy suggest that sabertooths and modern felids were ecologically distinct. Evidence from functional morphology and fossil associations elucidates the distinctions. Sabertooth incisor and carnassial morphology indicates extreme flesh specialisation and lack of bone-crushing ability. Sabertooth cranial morphology and fossil associations suggest a specialisation upon very large prey. The post-cranial morphology of sabertooths indicates a dense woodland and forest habitat preference. This implies that two distinct large carnivore communities existed in the Pliocene and early Pleistocene: a mixed and open habitat community composed of the ancestors of the extant carnivore community plus Chasmaporthetes, and a closed habitat community dominated by the sabertooths. Scavenging opportunities in the closed habitat community would have been much better than in more open habitats. Homo habilis with its inferred arboreal abilities could have passively scavenged very effectively in dense woodlands and forests. Paleoenvironmental and paleontological data indicate that these closed habitats shrunk after 1·7 million years ago and the sabertooths probably went extinct in sub-Saharan Africa. Homo habilis perhaps increasingly utilised more open habitats and would have been forced to confront large predators to gain adequate scavenging returns. Archaeological data of stone tool raw materials and site placement suggests that early hominids switched from an emphasis on dense woodland habitats to increased usage of more open habitats after 1·6 million years ago. Confrontational scavenging along with increased predation pressure may have contributed to the morphological changes associated with the shift to Homo erectus.

Models for European pleistocene hominid evolution

Patterns of primate socioecology have been used to suggest that the first truly savanna-dwelling hominin, Homo ergaster, lived in sizeable groups. Here, we revisit these estimates and infer additional features of the social organization of these early hominins based on anti-predator responses observed across the primate taxon. We first show that the effect of habitat on primate group size, composition, and sexual dimorphism is negligible after controlling for substrate use and phylogeny: terrestrial species live in larger groups with more and bigger males than arboreal taxa. We next hypothesize that groups can only survive in open habitats if males are able to engage in joint counter-attacks against the large carnivorans typical of such environments. To test this, we analyze reports on primate counter-attacks against known predators and find these are indeed disproportionately frequent in terrestrial taxa living in open habitats, sometimes even involving the use of tentative weapons. If we subsequently only examine the taxa that are particularly adept at this (chimpanzees and baboons), we find an effect of habitat type on group size: groups on the savanna are larger than those in the forest. We thus infer that H. ergaster lived in very large groups with many males that jointly defended the group against carnivorans, and argue that these counter-attacks will readily have turned into confrontational scavenging and cooperative hunting, allowing Homo to move into the niche of social carnivore. These two features (life in very large multi-male groups and a switch to persistent carnivory) shaped the evolution of our lineage to such an extent that the social organization of H. ergaster may already have contained many key elements characterizing modern day foragers: male bonding, incipient male–female friendships with food sharing, a tendency toward endogamy, and the presence of large communities that eventually turned into the ethno-linguistic units we can still recognize today.