Evolutionary Psychology Week 3 The Natural History of Humans Aim: To introduce to you the some of the facts of human natural history that give licence to the claim that human’s minds are evolved adaptations. Reward: You should have a fuller appreciation of the details of the evolution of your lineage and be able to generate hypotheses about psychological adaptations. Evolutionary Psychology Week 3 - The Natural History of Humans The EEA: Term coined by Bowlby (1969) & developed by Tooby & Cosmides (1990, ‘92) The EEA is the set of past selection pressures responsible for any given extant adaptation; i.e. analogous to the notion of ‘niche’ in evolutionary biology. EEA synonyms: the Pleistocene: ancestral environment: environment of selection: Plio-Pleistocene. In terms of time ... • sometimes relaxed to cover the c.6 million year period to cover the emergence of the family ‘hominoid’. • most often taken to be the c.2 million year period since the emergence of the genus Homo. Evolutionary Psychology Week 3 - The Natural History of Humans The EEA ... one can define the environment of evolutionary adaptedness for an adaptation as that set of selection pressures (i.e. of the ancestral world) that endured long enough to push each allele underlying the adaptation from its initial appearance to near fixation (Tooby & Cosmides, 1997). Evolutionary Psychology Week 3 - The Natural History of Humans The lineage Homo Australopithecines • Last common ancestor between the apes & us lived c 5 to 7 mya. • Earliest members of our lineage, the Australopithecines, from c 6 to c 2 mya. • The Australopithecines were bi-pedal but long arms, long, curved fingers & toe bones suggesting they were also arboreal. • The Australo. had brains approx. same size as modern great apes. • The Australo. were a highly adapted species in their own right. • robustus were contemporaneous with the earliest forms of Homo. Evolutionary Psychology Week 3 - The Natural History of Humans The lineage Homo Early Homo • The genus Homo is thought to have arisen from one of the gracile Australo.forms. • The first earliest Homo was habilis – appeared around 2 mya. • habilis ‘handy man’ the first to use tools. • Next was ergaster/erectus, with a further increase in brain size and larger stature, arose around 1.8 mya. • erectus had bigger brain, larger morph and was the first hominid to radiate out of Africa. • erectus appears to be the longest lived of Homo species to date – c 1.5 my’s. Evolutionary Psychology Week 3 - The Natural History of Humans The lineage Homo Homo sapien sapien • ‘Out-of-Africa’ (or ‘African Eve’ hypothesis) suggests all living humans share a recent common ancestor that lived in Africa c 100 000 to 200 000 years ago. • This species crossed the Levant land bridge around 70 000 years ago: At this point tool construction & use diversified. • Subsequently spread across Eurasia, into Australia, and, via the Bering Strait, into the America’s c15 000 years ago. Evolutionary Psychology Week 3 - The Natural History of Humans The lineage Homo Homo sapien sapien • The Out-of-Africa hypothesis suggests – Neanderthals of Europe and western Asia are not directly related to moderns. – That modern human races did not evolve from different populations of erectus. – That early sapien was distinct from predecessors by behavioural flexibility in the face of novel environments. Evolutionary Psychology Week 3 - The Natural History of Humans Where was the EEA? • Africa: More precisely, it is predominantly eastern and, to a lesser extent, southern African. • We cannot be as sure of its location as we can its duration: there is debate on the matter of where hominid development prior to modern man took place. • As a general rule take it that the EEA (or a functional equivalent) is being invoked (by you or any other) when any given account of our past or hypothesis concerning psychological adaptations makes an assumption(s) about: – a species of Homo, and/or – the environment to which it was adapted, and/or – the environment to which it needed to adapt. Evolutionary Psychology Week 3 - The Natural History of Humans Why is the EEA invoked? The EEA is a tacit admission that evolutionary theory in and of itself is not entirely adequate as a generator of hypotheses about psychological adaptations. It humanises evolutionary theory – By isolating the EEA as the Pleistocene we can be speciesspecific. It works as an adaptation generator – From our reproductive ecology we can infer the problems the brain has evolved to solve, and hypotheses the functional properties the brain is likely to have. Evolutionary Psychology Week 3 - The Natural History of Humans What can we say about the EEA? • We sought sex. • We exhibited nepotism. • We sought and, if necessary, competed for resources. Furthermore ... • Historically speaking, sex, kin and resource acquisition are what humans do. • Functionally speaking, sex, kin and resource acquisition are what humans are for. Evolutionary Psychology Week 3 - The Natural History of Humans What do we know about the EEA? • Hunter/gather and/or scavenging subsistence • Nomadic or semi-nomadic existence • Low population density • Small kin-based groupings • Simple technology • High infant mortality and low life expectancy • Vulnerability to the natural environment • Few lifestyle options. Evolutionary Psychology Week 3 - The Natural History of Humans Some points to note about the EEA • It always refers to the past – it is responsible for adaptations that evolved over thousands of generations and these are ‘tuned’ to recurrent aspects of past environments. • The past and the present are not identical – if the environment changes, then the adaptation may be ‘out of tune’ with the present environment and fail to properly perform its reproductive function. • It is an essential and logically necessary aspect of the theory of natural selection. Evolutionary Psychology Week 3 - The Natural History of Humans Recap • EP works on the assumption that the ‘past explains the present’ - the ‘past’ is called the EEA. • The EEA is the period between the emergence of Homo as a form and us as an instance. • The EEA is the conceptual bridge and ‘adaptation generator’ between what we were & what we are. • The EEA is also a maladaptation generator – it tells what we are not ‘fitted’ to. • What we can say about the EEA is constrained by the fossil record.