An ongoing conflict in sociology and anthropology exists between those who believe that human nature is competitive and brutal to the bitter end versus those who believe human nature is more cooperative and sociable, sharing resources of all types to secure the greater good. This might be recognizable to some as the perennial friction between citizen and society (alternatively, individualism and collectivism). Convincing evidence from human prehistory is difficult to uncover. Accordingly, much of the argument for competition comes from evolutionary biology, where concepts such as genetic fitness and reproductive success (and by inference, reproductive failure) are believed to motivate and justify behavior across the board. As the typical argument goes, inferior genes and males in particular who lack sexual access or otherwise fail to secure mates don’t survive into the next generation. Attributes passed onto each subsequent generation thus favor fitter, Type A brutes who out-compete weaker (read: more cooperative) candidates in an endless self-reinforcing and narrowing cycle. The alternative offered by others points to a wider gene pool based on collaboration and sharing of resources (including mates) that enables populations to thrive together better than individuals who attempt to go it alone or dominate.
Not having undertaken a formal study of anthropology (or more broadly, primatology), I can’t say how well this issue is settled in the professional, academic literature. Online, I often see explanations that are really just-so stories based on logic. What that means is that an ideal or guiding principle is described, something that just “makes sense,” and supporting evidence is then assumed or projected. For instance, we now know many of the mechanisms that function at the cellular level with respect to reproduction and genetic evolution. Those mechanisms are typically spun up to the level of the organism through pure argumentation and presumed to manifest in individual behaviors. Any discontinuity between aggregate characteristics and particular instances is ignored. Questions are solved through ideation (i.e., thought experiments). However, series of if-then statements that seem plausible when confronted initially often turn out to be pure conjecture rather than evidence. That’s a just-so story.
One of the reasons we look into prehistory for evidence of our true nature (understood as biology, not sociology, handily sweeping aside the nature/nurture question) is that hunter-gatherers (HGs) lived at subsistence level for a far longer period of our evolutionary history than our comparatively brief time within the bounty of civilization. It’s only when surpluses and excesses provide something worth hoarding, monopolizing, and protecting that hierarchies arise and/or leveling mechanisms are relaxed. Leaving Babylon has a discussion of this here. Some few HG cultures survive into the 21st century, but for most of us, The Agricultural Revolution is the branching point when competition began to assert itself, displacing sharing and other egalitarian impulses. Accordingly, the dog-eat-dog competition and inequality characteristic of the modern world is regarded by many as an exaptation, not our underlying nature.