Many groups continued their hunter-gatherer ways of life, although their numbers have perpetually declined partly as a result of pressure from growing agricultural and pastoral communities. A large part of them reside in arid regions and tropical forests in the developing world. Areas which were formerly unrestricted to hunter-gatherers were -and continue to be- encroached upon by the settlements of agriculturalists. In the resulting competition for land use, hunter-gatherer societies either adopted these practices or moved to other areas. Jared Diamond has also blamed a decline in the availability of wild foods, particularly animal resources. In North and South America, for example, most large mammal species had gone extinct by the end of the Pleistocene, according to Diamond, because of overexploitation by humans, although the overkill hypothesis he advocates is strongly contested.
As the number and size of many agricultural societies increased, they expanded into lands traditionally used by hunter-gatherers. This process of agriculture-driven expansion soon led to the development of complex forms of government in agricultural centers such as the Fertile Crescent, Ancient India, Ancient China, Olmec, and Norte Chico; and set in motion the impetus for further expansion through warfare and colonization.
As a result of the now near-universal human reliance upon agriculture, the few contemporary hunter-gatherer cultures usually live in areas seen as undesirable for agricultural use.
Others, such as the Haida of present-day British Columbia, lived in such a rich environment that they could remain sedentary, like many other Native Americans of the Pacific Northwest coast. These groups demonstrate more hierarchical social organization.
War in hunter-gatherer societies is usually caused by grudges and vendettas rather than for territory or economic benefit.
A vast amount of ethnographic and archaeological evidence demonstrates that the sexual division of labor in which men hunt and women gather wild fruits and vegetables is an extremely common phenomenon among hunter-gatherers worldwide, but there are a number of documented exceptions to this general pattern. A study done on the Aeta people of the Philippines states, "About 85% of Philippine Aeta women hunt, and they hunt the same quarry as men. Aeta women hunt in groups and with dogs, and have a 31% success rate as opposed to 17% for men. Their rates are even better when they combine forces with men: mixed hunting groups have a full 41% success rate among the Aeta.". It was also found that among the Ju'/hoansi people of Namibia that women helped the men during hunting by helping them track down quarry. Moreover, recent archaeological research done by the anthropologist and archaeologist Steven Kuhn from the University of Arizona suggests that the sexual division of labor did not exist prior to the Upper Paleolithic and developed relatively recently in human history. The sexual division of labor may have arisen to allow humans to acquire food and other resources more efficiently. It would, therefore, be an over-generalization to say that men always hunt and women always gather.
At the 1966 "Man the Hunter" conference, anthropologists Richard Borshay Lee and Irven DeVore suggested that egalitarianism was one of several central characteristics of nomadic hunting and gathering societies because mobility requires minimization of material possessions throughout a population; therefore, there was no surplus of resources to be accumulated by any single member. Other characteristics Lee and DeVore proposed were flux in territorial boundaries as well as in demographic composition. At the same conference, Marshall Sahlins presented a paper entitled, "Notes on the Original Affluent Society," in which he challenged the popular view of hunter-gatherers living lives "solitary, poor, nasty, brutish and short," as Thomas Hobbes had put it in 1651. According to Sahlins, ethnographic data indicated that hunter-gatherers worked far fewer hours and enjoyed more leisure than typical members of industrial society, and they still ate well. Their "affluence" came from the idea that they are satisfied with very little in the material sense. This, he said, constituted a Zen economy.
One way to divide hunter-gatherer groups is by their return systems. James Woodburn uses the categories "immediate return" hunter-gatherers for egalitarian and "delayed return" for nonegalitarian. Immediate return foragers consume their food within a day or two after they procure it. Delayed return foragers store the surplus food (Kelly, 31). Some Marxists have theorised that hunter-gatherers would have used primitive communism and anarcho-primitivists elaborate the mechanics further by asserting it would have been a gift economy, (although this would not have applied for all hunter-gatherer societies.) Mutual exchange and sharing of resources (I.e. meat gained from hunting) are important in the economic systems of Hunter gatherer societies.
On the other hand, that hunter-gatherer societies seem to manifest significant variability as studies in relatively modern times clearly support, does not allow us to generalize about the extent of variability characteristic of the human Environment of Evolutionary Adaptedness (EEA) that is so important to the development of evolutionary psychological theory. The hunter-gatherer cultures examined today have had much contact with modern civilization and do not represent to "pristine" original human culture (see succeeding paragraphs re: post-agricultural effect on original hunter-gatherers). Much variability we now see in hunter-gatherers is also the result of this mode of living being carried into environmental conditions significantly divergent from our original habitat. Unlike other primates still living in warm climate conditions within Africa, the human primate has moved far beyond the realm of his original EEA ---the Inuit are a clear example of hunter-gatherers clearly divergent from the human EEA (understandably, there was little "gathering" of vegetation among the Inuit). Yet it may well be that, like the more rigidly defined social structures of other primates, our original social behaviors did not diverge so significantly from one nomadic family to the next in the EEA. So the point of not generalizing until more data is forthcoming extends not only to the possible behavioral consistency of social patterns in the human EEA, but also to possible behavioral variability of such social patterns.
The transition from hunting and gathering to agriculture is not necessarily a one way process. It has been argued that hunting and gathering represents an adaptive strategy which may still be exploited, if necessary, when environmental change causes extreme food stress for agriculturalists.
In fact, it is sometimes difficult to draw a clear line between agricultural and hunter-gatherer societies, especially since the widespread adoption of agriculture and resulting cultural diffusion that has occurred in the last 10,000 years. Many hunter-gatherers consciously manipulate the landscape through cutting or burning undesirable plants while encouraging desirable ones, some even going to the extent of slash-and-burn to create habitat for game animals. These activities are on an entirely different scale than those associated with agriculture, but they are nevertheless domestication on some level. Today, almost all hunter-gatherers depend to some extent upon domesticated food sources either produced part-time or traded for products acquired in the wild. Some agriculturalists also regularly hunt and gather (e.g. farming during the frost-free season and hunting during the winter). Still others in developed countries go hunting, primarily for leisure. In the Brazilian rainforest, groups which recently or continue to rely on hunting and gathering techniques seem to have adopted this lifestyle, abandoning most agriculture, as a way to escape colonial control and as a result of the introduction of European diseases reducing their populations to levels where agriculture became difficult.
Some of the theorists who advocate this “revisionist” critique imply that, because the "pure hunter-gatherer" disappeared not long after colonial (or even agricultural) contact began, nothing meaningful can be learned about prehistoric hunter-gatherers from studies of modern ones (Kelly, 24-29; see Wilmsen); however, most specialists who study hunter-gatherer ecology (see cultural ecology and human behavioral ecology) disagree with this conclusion. As well, Lee and Guenther have refuted most of the arguments put forward by Wilmsen and currently the revisionist school has been largely discredited.
There are contemporary hunter-gatherer peoples who, after contact with other societies, continue their ways of life with very little external influence. One such group is the Pila Nguru or the Spinifex People of Western Australia, whose habitat in the Great Victoria Desert has proved unsuitable for European agriculture (and even pastoralism). Another are the Sentinelese of the Andaman Islands in the Indian Ocean, who live on North Sentinel Island and to date have maintained their independent existence, repelling attempts to engage with and contact them.