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(Female narrator) Where do we look to find the roots of behavior?
Are we born a blank slate and then taught everything we know?
Or, do we enter the world with some inclinations? 
Some innate stirrings?
Some idea of what to look for and how to act?
For evolutionary psychologists, the answers to some of the 
 most fundamental questions of nature versus nurture
may be found in our evolutionary history.
Darwin's theory of natural selection has been 
the organizing principle in biology for a long time.
In psychology, too, Darwin's evolutionary 
principles can help explain human behavior.
So the basics of the Darwinian theory
are that we're not all the same at any point of time
for any given species, different individuals in the species vary
and the variations may be better or worse fits to 
 the environment in which they happen to live.
The organisms who happen to have features that 
 are particularly good fits to their environment...
the environment has nuts and berries that are hard to get to...
and they've got big, long beaks, if they're birds, 
 they're more likely to survive and reproduce.
So that organism doesn't change. But the population of organisms 
 changes because an organism with a particular feature
is more likely to have offspring and after a few generations of that
the population shifts so that the features that work in 
 that environment becomes the dominant feature for the species.
And so this species, across generations, kind of shifts in its 
 features through a process that Darwin called "natural selection."
The core idea for evolutionary psychology is that evolution 
 gives us certain capacities, or perhaps mechanisms.
They don't necessarily give us a tendency 
to do a behavior over and over,
but a CAPACITY to do a behavior in a particular kind of setting.
(Narrator) Two of the most powerful tools in Evolutionary 
 Psychology are the studies of Homology and Analogy.
A homology is a similarity that exists between two species
because of their common ancestry.
For example, the color vision we share with our ape ancestors.
An evolutionary analysis does a couple of things.
One of them is to point out that, of course, as humans, 
 we're something else that evolved in an evolution of species.
It might be that there's something analogous between a 
 human being behavior and some other species.
One simple example... social organizations 
in the human case commonly are hierarchical.
One simple example... social organizations in the human case commonly are hierarchical. 
That process, in which there's a social group that's organized 
 seems not at all like something that develops
wrung out of the brains in the human 
 beings over the past few thousand years
but is so closely analogous to what you see 
 in the case of our related ancestor apes.
(Narrator) An analogy is any similarity that stems 
not from common ancestry, but from two different species
because of some similarity in their habitats or lifestyle 
 involving a common characteristic independent of one another.
For example, the wings of birds and insects are analogous.
These species adapted to fly through different evolutionary paths.
So wing structure did not evolve from a common ancestor, 
 but rather through independent adaptation, making it an analogy.
Something that intrigues evolutionary psychologists is the phenomenon of helping one another, or being altruistic.
The answer as to why we see altruistic behavior across species 
is packaged into two theories; the kin selection theory 
and the reciprocity theory.
The reciprocity theory provides an account 
of how acts of altruism can arise.
What evolutionary psychology does is to tell us that
a) it's not irrational to be altruistic, and b) one doesn't NEED 
 to explain it in terms of a contemporary moral code
because it may be kind of wired in for evolutionary reasons.
Then you ask, why would that be wired in?
One is that the behavior that's altruistic today may be 
 paid off through behavior that benefits you, tomorrow.
There may be reciprocity.
The second possibility is that the altruistic act 
if directed towards relatives, or kin, 
pays off in terms of the survival of the genetic lineage.
Your family... your collection of genes is in good shape if your 
 altruistic act saves two sisters and three brothers and four children.
They all survive at the cost of you... but across the course 
 of evolution, if you imagine genes trying to survive,
then altruism is doing that survival for you -
you're paying off the kin and the genetic system in 
 the long run, through your own altruistic act.
(Narrator) Altruism is just one example of the implications of 
 studying behavior through the lens of evolutionary psychology.
The same techniques of cross-species 
analysis and evolutionary probing
have led to important hypotheses about gender differences, 
 mating patterns, and aggression among other traits.
Given that those differences occur 
as a natural feature of human biology,
it may be that, for men and women, there are 
 different kinds of behaviors that make most sense.
The evolutionary psychology argument is that
if women are particularly burdened with the cost of pregnancy
then, when looking for mates, they will be particularly attuned to 
 mates who can help out with those burdens...
will be financially successful...
and then the predictions of evolutionary psychology is 
that possession of financial resources, in the game of mating,
are going to be extremely important for men in 
 attracting women, but not as much vice versa.
And that's not a learned contemporary thing. 
That reflects our evolutionary heritage.
(Narrator) The usefulness of evolutionary psychology
is in its ability to generate hypotheses about current behaviors 
by looking at the past as our greatest source of insight 
into the present.
But we must also be wary of some of the potential
pitfalls of the evolutionary approach to psychology.
Evolutionary psychology often explains why,
in a particular situation, a particular kind of behavior occurs
because, evolutionarily, that paid off.
However, much of psychology involves other questions 
that just aren't touched by the evolutionary psychologist.
For example, much of everyday behavior involves 
figuring out the situation you're in in the first place.
Are these people your friends, or not?
Are they useful mates, if you're trying to date, or are they not?
Often there's a lot of ambiguities to life.
So the trick for evolutionary psychology that is the challenge is 
 to figure out whether the story about natural selection behavior
was one that is actually mapping onto that long-ago process
or is some misplaced story because the behavior really 
was a kind of quirky thing that doesn't deserve to have 
a natural selection story in the first place.
(Narrator) The insights of evolutionary psychology 
are not end-all explanations.
They are frameworks in organizing principles 
through which we can begin to answer 
some of the deepest questions of human behavior.
