Human Behavior: Applying an Evolutionary Perspective
Evolutionary Psychology
The goal of research in evolutionary psychology is to discover
and understand the design of the human mind. Evolutionary
psychology is an approach to psychology, in which knowledge
and principles from evolutionary biology are put to use in
research on the structure of the human mind…
In this view, the mind is a set of
information-processing machines that
were designed by natural selection
to solve adaptive problems faced by
our hunter-gatherer ancestors…
An evolutionary approach allows
one to recognize … natural
competences … it indicates that
the mind is a heterogeneous collection
of these competences and, most
importantly, it provides positive
theories of their designs.”
Darwin and James
Darwin (1860): “In the distant future … Psychology will
be based on a new foundation”, i.e., evolution.
William James (Principles of Psychology, 1890):
‘instincts’ = ~ specialized neural circuits common to all
members of the species, a product of the species’
evolutionary history
‘instincts’ taken together = ~ human nature
James ‘instincts’ are similar to Haidt’s ‘intuitions’
The Standard Social Science Model (SSSM)
“Both before and after Darwin, a
common view among
philosophers and scientists has
been that the human mind
resembles a blank slate, virtually
free of content
until written on
by the hand of
experience …
The Standard Social Science Model (SSSM)
Over the years, the technological metaphor used to describe the
structure of the human mind has been consistently updated, from
blank slate to switchboard to general purpose computer, but the
central tenet … has remained the same … [and] has become the
reigning orthodoxy in mainstream anthropology, sociology, and
most areas of psychology… According to this orthodoxy:
all of the specific content of the human mind originally derives
from the "outside" – from the environment and the social world –
and the evolved architecture of the mind consists solely or
predominantly of a small number of general purpose
mechanisms that are content-independent, and which sail under
names such as … 'learning,' 'intelligence,' 'imitation,‘ culture‘…
SSSM versus EP
SSSM: Same general-purpose mechanisms govern all
psychological tasks (except basic perception, language),
e.g., how one
• learns language
• learns to recognize emotional expressions
• thinks about incest
• acquires ideas and attitudes about friends and reciprocity
Mechanisms of reasoning, learning, and memory operate
uniformly – they are content-independent or domain-general.
EP: All normal human minds reliably develop a collection of
domain-specific reasoning and regulatory circuits. “These
circuits organize the way we interpret our experiences, inject
certain recurrent concepts and motivations into our mental
life, and provide universal frames of meaning that allow us to
understand the actions and intentions of others”.
Five Principles
Principle 1: The brain is a physical system. It functions as a
computer. Its circuits are designed to generate behavior that
is appropriate to your environmental circumstances.
Principle 2: Our neural circuits were designed by natural
selection to solve problems that our ancestors faced during
our species' evolutionary history.
“The reason we have one set of circuits rather than another is
that the circuits that we have were better at solving problems
that our ancestors faced during our species' evolutionary
history than alternative circuits were”.
For example, just as natural selection has shaped dung flies
to approach dung, it has shaped us to avoid it.
Five Principles
Principle 2: Our neural circuits were designed by natural
selection to solve problems that our ancestors faced during our
species' evolutionary history.
Designed to solve adaptive problems, i.e., problems
• that cropped up again and again during the evolutionary
history of a species
• whose solution affected the reproduction of individual
organisms
“Obviously, we are able to solve problems that no huntergatherer ever had to solve – we can learn math, drive cars,
use computers. Our ability to solve other kinds of problems is a
side-effect or by-product of circuits that were designed to solve
adaptive problems. For example, the fact that we can surf and
skateboard are mere by-products of adaptations designed for
balancing while walking on two legs”.
Five Principles
Principle 3: Consciousness is just the tip of the iceberg; most
of what goes on in your mind is hidden from you. As a result,
your conscious experience can mislead you into thinking that
our circuitry is simpler that it really is. Most problems that you
experience as easy to solve are very difficult to solve – they
require very complicated neural circuitry.
Principle 4: Different neural circuits are specialized for
solving different adaptive problems.
“A basic engineering principle is that the same machine is
rarely capable of solving two different problems equally well.
We have both screw drivers and saws because each solves
a particular problem better than the other”.
Five Principles
Principle 4: Different neural circuits are specialized for
solving different adaptive problems.
Five Principles
• “Until recently, it was thought that perception and, perhaps,
language were the only activities caused by cognitive
processes that are specialized. Other cognitive functions –
learning, reasoning, decision-making – were thought to be
accomplished by circuits that are very general purpose”.
• "General intelligence" – a hypothetical faculty composed of
simple reasoning circuits that are few in number, contentindependent, and general purpose
• “Crib sheets” or privileged hypotheses
• Babies < 1 yo assume that the self-propelled movement of
animate objects is caused by invisible internal states –
goals and intentions – whose presence must be inferred,
since internal states cannot be seen.
• Toddlers have a well-developed "mind-reading" system
(impaired in autism)
Five Principles
Principle 5: Our modern skulls house a stone age mind.
“Natural selection, the process that designed our brain, takes
a long time to design a circuit of any complexity. The time it
takes to build circuits that are suited to a given environment is
so slow it is hard to even imagine – it's like a stone being
sculpted by wind-blown sand. Even relatively simple changes
can take tens of thousands of years. “
Actually evidence is accumulating in many areas
that selection can occur quickly, at least sometimes.
The Environment of Evolutionary Adaptedness (EEA):
Hunter-gatherer (foraging) societies of the African savanna.
Environment of Evolutionary Adaptedness (EEA)
Hunter-gatherer (foraging) society: Subsistence gained from hunting
animals, fishing, and gathering edible plants in the wild. Small, simple band
level of social organization. Hunting and gathering is thought to have been
the only subsistence strategy employed by human societies for more than
two million years, from the Paleolithic until the end of the Mesolithic period.
As recently as 15,000 years ago, everyone in the world lived by foraging.
The transition into the subsequent Neolithic period is chiefly defined by the
development of agricultural practices (~ 10,000 years ago).
Environment of Evolutionary Adaptedness (EEA)
“The environment that humans – and, therefore, human minds – evolved in
was very different from our modern environment. Our ancestors spent well
over 99% of our species' evolutionary history living in hunter-gatherer
societies. That means that our forbearers lived in small, nomadic bands of a
few dozen individuals who got all of their food each day by gathering plants
or by hunting animals. Each of our ancestors was, in effect, on a camping
trip that lasted an entire lifetime, and this way of life endured for most of the
last 10 million years.” Cosmides & Toobey: Evolutionary Psychology: A Primer
Environment of Evolutionary Adaptedness (EEA)
“Our species lived as hunter-gatherers 1000 times longer than
as anything else. The world that seems so familiar to you and
me, a world with roads, schools, grocery stores, factories,
farms, and nation-states, has lasted for only an eye blink of
time when compared to our entire evolutionary history.
… Natural selection is a slow process, and there just haven't
been enough generations for it to design circuits that are welladapted to our post-industrial life …
In other words, our modern skulls house a stone age mind.
The key to understanding how the modern mind works is to
realize that its circuits were not designed to solve the day-today problems of a modern American – they were designed to
solve the day-to-day problems of our hunter-gatherer
ancestors.”
Cosmides & Toobey: Evolutionary Psychology: A Primer
Environment of Evolutionary Adaptedness (EEA)
“Evolutionary psychology is relentlessly past-oriented.
Cognitive mechanisms that exist because they solved
problems efficiently in the past will not necessarily generate
adaptive behavior in the present.
Indeed, EPs reject the notion that one has "explained" a
behavior pattern by showing that it promotes fitness under
modern conditions …
Cosmides & Toobey: Evolutionary Psychology: A Primer
Environment of Evolutionary Adaptedness (EEA)
Key point: mismatches between modern environments and
the EEA will inevitably compromise the effectiveness of human
adaptations that evolved in the EEA = adaptive lag.
“In practice, the evolutionary part of EP often reduces to rather vague
claims about selective conditions in the EEA that may have favoured
the evolution of a hypothesized psychological mechanism … To the
extent that our knowledge of the EEA remains sketchy, rigorous
quantitative testing of precise selectionist hypotheses becomes
virtually impossible, and the result can easily degenerate into adaptive
storytelling”.
Smith et al 2000
Design Features
“Knowledge of adaptive function is necessary for carving
nature at the joints.”
(Note: Neuroethology operates on this same principle!)
Design evidence. Adaptations are problem-solving machines,
and can be identified using the same standards of evidence
that one would use to recognize a human-made machine:
design evidence.
Nature and nurture: An adaptationist perspective
Evolutionary psychology is not just another swing of the
nature/nurture pendulum. A defining characteristic of the field
is the explicit rejection of the usual nature/nurture
dichotomies – instinct vs. reasoning, innate vs. learned,
biological vs. cultural.
Reasoning instincts: An example
Wason Selection Task: Subject is asked to look for violations
of a conditional rule of the form If P then Q.
Rule: "If a card has an even number on one face, then its
opposite face is red”.
Which card(s) must be turned over to see if this rule has
been violated.
‘8’ and brown cards – only ~25% of subjects get this right!
Reasoning instincts: An example
Wason Selection Task: Subject is asked to look for violations
of a conditional rule of the form If P then Q.
Rule: "If a Cambridge resident goes into Boston, then that
person takes the subway.”
Boston
Arlington
subway
cab
Each card represents one person. One side of a card tells
where a person went, and the other side of the card tells how
that person got there.
Indicate only those card(s) you definitely need to turn over to
see if any of these people violate this rule.
Boston & cab cards – only ~25% of subjects get this right!
Reasoning instincts: An example
Wason Selection Task: Subject is asked to look for violations
of a conditional rule of the form If P then Q.
People who ordinarily cannot detect violations of if-then rules
can do so easily and accurately when that violation represents
cheating in a situation of social exchange/contract
Rule: "If you are drinking alcohol then you must be 21"
17
21
Drinking
Beer
Drinking
Coke
Indicate only those card(s) you definitely need to turn over
to see if any of these people violate this rule.
17 & drinking beer – most people get this right!
Reasoning instincts: An example
Social contract form again…
Which of the following cards do you need to turn over to
either confirm or falsify the hypothesis that If you charge a
purchase on your credit card, you must pay the bill.
Person
charges
purchase
Person
doesn’t
charge
Person
pays
bill
Person
doesn’t
pay bill
Most people get the right answer!
Summing Up: Tenets of Evolutionary Psychology
1. Psychological mechanisms – not behaviors – have been
shaped by natural selection to enhance reproductive
success.
Genes
Ψ Mechanisms
Natural
selection
behaviors
fitness
Tenets of Evolutionary Psychology
1. Psychological mechanisms – not behaviors – have been
shaped by natural selection to enhance reproductive
success.
2. Mechanisms have many effects (‘side effects’) besides the
favorable (selected) effects. And these side effects can be
maladaptive.
3. The historical ecological context (EEA) in which human
evolution occurred is different from the contemporary
context, especially those of “modern” societies.
4. Therefore, a given trait may be:
(a) adaptive;
(b) a maladaptive side effect of an otherwise adaptive
mechanism; or
(c) a maladaptive interaction of an out-of-date adaptive
mechanism with a new environmental context.
Evolutionary Psychology vs. Human Behavioral Ecology
EP
HBE
Daly & Wilson 1999 vs. Smith, Borgerhoff Mulder & Hill 2000
Evolutionary Psychology vs. Human Behavioral Ecology
Two Contrasting but (I think) Complementary
Evolutionary Perspectives on Human Behavior:
Evolutionary Psychology (EP) – derived from a
synthesis of biology and psychology
Human Behavioral Ecology (HEB) – derived from a
synthesis of biology and anthropology
Note: In my view both of these viewpoints, though noncomplementary on some issues, can be combined into a
general ‘evolutionary psychology’ (no caps!)
Evolutionary
Psychology
Human
Behavioral Ecology
Focus on
Universals
Variation/Diversity
Assumed
Selective
Environment
Environment of
Evolutionary
Adaptedness
Present
Environment
How measure
Adaptation?
Design Criteria
(re EEA)
Reproductive Success
or ‘Fitness’
Usual study
population
Modern societies
Traditional societies
Smith, Borgerhoff-Mulder & Hill (2000) Evolutionary analyses of
human behaviour: a commentary on Daly & Wilson. Anim Behav
Contrast Evolutionary Psychology (EP) and Human
Behavioral Ecology (HBE).
To considerable extent EP and HBE are complementary,
differing in relative emphasis placed on psychological
mechanism versus manifest behavior
But they diverge in other, controversial ways:
1. Use of formal models and deductive theory (HBE)
2. Emphasis on domain-specific cognitive algorithms (EP)
3. Relationship between psychological mechanisms and
observed behavior (EP)
4. Assertions regarding adaptive lag and adaptation to past
environments (EP HBE)
5. Views on the relevance of fitness measures to analyses of
contemporary behavior. (EP HBE)