Animal Behavior/Human Evolution

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[edit] Human Evolution

"In the distant future ... psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history" -- Charles Darwin, 1859^[1]

Biological evolution has led to the emergence of humans as a distinct species from other primates. The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually also include other groups, such as the australopithecine hominids.

Humans emerged as a distinct lineage from among the other great apes around 4-7 million years ago, most likely in Eastern Africa. The earliest undisputed hominins emerged 4.4 million years ago, the earliest members of Homo arose 2.5 million years ago, while our species, Homo sapiens, is not older than 200,000 years. Although considerable questions remain, a consistent picture is slowly emerging. Ancestral hominins occupied mostly forested habitats, depended on a largely fruit-based diet, and lived in small, migratory, male dominated, social groups. Around 5 million years ago geological uplifting along the rift valley, along with increasingly drier and cooler climatic conditions of the pliocene, resulted in an expansion of savanna ecosystems across eastern Africa. Trees became more widely spaced, and allowed sufficient light to reach the ground for an unbroken herbaceous layer dominated by grasses. Australopithecines appear to have ventured out into these more open woodlands in search of the ungulate fauna thriving there. A variety of ecological demands contributed to rapid specializations in a host of morphological and behavioral traits. Footprints, preserved at Laetoli, Tanzania, when rain cemented powdery volcanic ash from a recent eruption into a layer of tuff, evidence that autralopithecines already lacked the mobile big toe of apes, had an arch more typical of modern humans, and habitually walked upright. With the advent of bipedal walk, the acquisition of a larger skull cavity helped balance the head during running. Australopithecines included meat into an increasingly omnivorous diet and coordinated group hunting efforts may have hastened the development of many critical skills ranging from communication, group cohesion, sophistication in hunting, to general problem solving. The emergence of fairly small, complex social units, with increasingly egalitarian roles of the sexes, encouraged the development of skills for allowing members to better navigate alliances, deception, warfare, cannibalism, as well as sharing, teaching, and compassion.

The genus Homo diverged from the australopithecines about 2.5 million years ago and began to exhibit a particular curiosity for exploring new terrains. The recent discovery of 1.5M year old hominid tracks at Lake Turkana^[2] show that such efforts were aided by highly efficient bipedal walk, combined with a surprisingly modern foot. Early expansions include those from now extinct species such as Homo erectus, which inhabited Asia, and Homo neanderthalensis, which inhabited Europe. The earliest known stone tools date to around 1.8 million years as they emerged in both Africa and Malaysia. Neanderthals were hunter-gatherers who moved across Europe following the advancing and retreating glaciers of the ice age. Adapted to temperate, northern climates success largely hinged on warmer interglacial periods. Total population probably never exceeded 100,000 and artifacts remain scarce even as its members began to develop finely-tuned technologies for creating a variety of flint-tools. The presence of Neanderthal weapons in animal bone show a level of hunting sophistication that allowed them to harvest even such large game as elephants, rhinoceros, and horses. It is also now clear that Neanderthals must have cared for injured group members, conducted simple burials, and showed an appreciation for art including carvings, beads, and music. Discussion continues on whether Neanderthals were able to communicate using a spoken language, but their hyoid bones, involved in speech, were basically identical to those of modern humans. 40,000 years ago another major African expansion of hominins lead modern humans from the taxon Homo sapiens to Europe which eclipsed Neanderthals with a number of advanced and sophisticated technologies, The rise of the new arrivals (Cro-Magnons) parallels the decline and eventual vanishing of Neanderthal culture, although whether through extinction or by intermixing with modern humans remains unclear.

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