Cosa ci ha resi così speciali? La traiettoria evolutiva degli umani fra genetica e cultura

Abstract

Modern humans are the only living representatives of hominins (Hominina), a primate lineage that diverged from chimps (Panina) between 5 and 7 million years ago (MA) in Central Africa. The main diagnostic trait of hominins is bipedal locomotion (bipedality). The genus Homo appeared in Central-Southern Africa around 2.5 MA and diversified into several species. Early traits of Homo included enhanced bipedality, anatomical modifications of arms and torso for high-speed throwing, and an increase in the relative size of the brain (encephalization quotient, or EQ). Bipedality and high-speed throwing were already present in modern form in H. erectus about 1 MA. The EQ continued increasing up to a maximum value attained in H. sapiens and H. neanderthalensis around 300,000 years ago. It is widely acknowledged that brain enlargement was made possible by reciprocal cooperation (ultrasociality), a novel form of cooperation independent of kinship or immediate benefits. The mainstream model posits that the emergence of multifamily groups based on reciprocal cooperation including cooperative breeding fostered brain enlargement under selection pressure for better social skills. Concurrently, in a complex network of causes and effects, this led to the evolution of language, a highly symbolic system of communication unique to humans. According to the hypothesis of group cultural selection and the more recent multilevel selection model, reciprocal cooperation
emerged from group selection favouring the enforcement of social norms. Many evolutionary biologists, however, reject the idea that group selection affects genetic evolution. Moreover, behavioural norms could only emerge in already integrated social groups. An alternative model suggests that high-speed throwing suppressed the archaic social hierarchy based on one-to-one close physical confrontation, thus producing a selection pressure for reciprocal cooperation and behavioural norms very early in human evolution. Cooperation, language and enhanced cognitive functions endowed human societies with cultural intelligence, the ability to accumulate knowledge across generations. This afforded humans access to cultural niche, a novel ecological niche partly physical and partly cognitive, in which cultural evolution is the main driver of adaptive change. War, defined as violent organized competition between politically independent groups, has been pivotal to the emergence of complex societies. The reason of the amazing success of our species lies not in the power of individual minds, but in the “collective brain” of our societies.