Transcript 3 The Natural History of Humans

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.