Like chimpanzees and bonobos, humans are omnivorous; this means that humans and chimpanzees kill other animals for food in addition to eating a wide variety of plants. Essentially, the human body is similar to that of the great apes; humans have the same arrangement of internal organs and bones, share several important blood types and suffer from many of the same diseases. However, there is a significant difference in the amount of meat that humans eat compared to chimpanzees. While chimpanzees extract at most 5 to 10 per cent of their calories from animals (including both small monkeys and termites extracted with tools), Homo erectus obtained most energy from meat (either from scavenging or from hunting). This heavy reliance on meat lasted until very recently, when agriculture appeared. There are only a handful of human populations (fewer than fifty across the globe) still able to survive without agriculture: they are known as hunter-gatherers.
omnivorous Ability to eat and survive on both plant and animal matter
hunter-gatherers Members of a nomadic people who live chiefly by hunting and fishing and harvesting wild food
STOP & THINK
What are the advantages of an omnivorous diet?
Competitiveness, hierarchy and aggression
One controversial characteristic that we may share with other primates is the potential for aggression. Field studies have shown differences among nonhuman primate species in the incidence and circumstances of actual intraspecific (within-species) violence. In anthropology, there has been much debate about the human capacity for violence and aggression. Sociobiology, for example, is an area of scientific research and thinking that claims that some social behaviour is a product of evolution (although not all sociobiologists agree on the extent of this). Some argue that certain behaviours (such as aggression and competitiveness) may have been advantageous to human survival. E. O. Wilson (1978), one of the founders of modern sociobiology, described some behaviours thought to be human universals as genetically based, such as male–female bonds, male dominance over females and aggression. These claims have been disputed by many human scientists, who have shown that there is much more variation in patterns of social behaviour across human societies.
sociobiology An area of biology that aims to explain social behaviour in terms of evolution
More recently, biological anthropologists such as Richard Wrangham and Dale Peterson (1997) have argued that violence played an important role in the evolution of humans and chimpanzees. However, such views have been heavily criticized for their lack of supporting evidence. An alternative view gaining strength in evolutionary anthropology is that our capacity for cooperation is what made humans behaviourally unique. While other species of primates mostly show alliances among closely related kin, studies of hunter-gatherers have shown that we frequently exhibit cooperative behaviours (such as food-sharing) towards those who are unrelated. Some of us are even able to display cooperation and altruism towards unknown individuals (think about giving blood or about charity work). The reasons for the coexistence of extreme cooperation and aggression in human societies is one of the most debated issues in evolutionary anthropology.
Social relations
Humans and some nonhuman primates share certain similarities in their behaviour towards each other. However, social behaviour varies from species to species. Two examples of nonhuman primate behaviour are explored here: of bonobos and of chimpanzees, our two closest evolutionary relatives.
Chimpanzees
(Matthew Hoelscher / Wikimedia Commons)
Common chimpanzees, living in tropical forests of Africa, live in small communities. These typically range from 20 to more than 150 members; however, chimpanzees spend most of their time travelling in small, temporary groups consisting of a few individuals that are made up of any combination of ages and sexes. Both males and females will sometimes travel alone. Chimpanzees, like humans, have complex social relationships and spend a large amount of time grooming each other. Grooming is an important way in which alliances are built.
Chimpanzee society shows considerable male dominance. Interestingly, male aggression has an important function in establishing a social hierarchy. However, aggression is often only displayed rather than followed through with violence. Males maintain and improve their social position by forming coalitions. These coalitions increase their influence, giving them power that they would not be able to gain alone. Social hierarchies among adult females tend to be weaker. Nevertheless, the status of an adult female may be important for her offspring.
Chimpanzees have been described as highly territorial and have been known to kill other chimps for territorial dominance, although there is some suggestion that highly aggressive behaviour by chimpanzees happens only when artificial feeding occurs.
A female may mate with several males, though a dominant male may stop other males gaining access to the female with whom they are consorting. Infanticide (the killing of babies) has been recorded among chimpanzees. This is often carried out by male coalitions that invade an existing
the gradual reduction in human sexual dimorphism.
