Transcript The Biological Roots of Behavior

The Biological Roots of Behavior
Part I: the complex interaction between
our genes and the environment to the
music of evolution
Genetics
the basics
• Chromosomes – strands of hereditary
material
• Humans have 46 – 23 from their mother,
23 from their father
• Found in the nucleus of each cell
• The master blueprint or recipe for each
individual
Genetic basics ii
• Genes – sections along a chromosome
which control the chemical reactions that
direct development
• Humans have around 25,000
• Composed of DNA
• Play an essential role in not only in how
we develop, but when we develop, as
switches, turning other genes off & on
2001- the Human Genome Project
Does one gene control anything?
• Media reports seem to indicate that certain
genes are responsible for certain traits or
abilities.
• True or false?
• Very few traits or abilities are controlled by
a single gene, most rely on an interaction
between several genes and the
environment.
Nature vs. nurture ?
• Is the person we are today a result of the
genes we inherited from our parents?
• Or, instead, are our traits, abilities,
strengths and weaknesses caused by our
environment?
• This question, which caused furious
debate for centuries, has been answered.
A mysterious dance
• Now we know that neither nature (genes)
nor nurture (the environment) are primarily
responsible for the person we are.
• A complex, ever-changing, interaction
between these two forces creates the
complex, unique people we are today,
ready to change as our lives and
circumstances do.
Why are we so similar?
• 6 billion and counting, yet we are
remarkably alike
• How can this be?
• Evolutionary psychologists claim that
this is due to genetic qualities, carried in
our DNA that developed while we evolved
from our ancestors
Mental Modules
• Evolutionary psychologists - mind not as a
general-purpose computer waiting to be
programmed by our experiences
• Instead, a collection of specialized and
independent modules developed to solve
specific survival problems
• One module often involves different parts
of the brain working together
Born to conquer
• These mental modules are put into place
by messages from our DNA as we mature
• They allow us to be proficient at various
tasks and abilities without much, or any,
experience or teaching
We all share …
• Without any work or effort, and at an early
age, humans show certain characteristics:
a) Infant reflexes – no one needs to
teach us to nurse
b) curiosity – we are eager to try new
things and manipulate objects
c) play – develops physical/social skills
Our innate cognitive tool set
• At birth we can:
a) interpret gestures & expressions,
b) identify faces,
c) understand what others are thinking
or feeling,
d) understand, to some extent, numbers;
e) acquire language
The wonder and mystery of
Language
• How do we readily turn random sounds
into words and sentences that convey
thoughts, feelings and complex
information?
• Darwin said that there is something unique
and special about the human brain that
allows a baby, with limited aide from the
environment, quickly master language.
Don’t animals have language?
• Yes, but only in a limited sense.
• Chimpanzees, gorillas and even parrots
can, with exhaustive coaching, pick up
many aspects of language
• But it’s not easy or natural
• Humans, on the other hand, develop
extraordinary language abilities naturally
given the most basic of opportunities
Language’s key ability
• But still, many animals communicate in
their environment, isn’t that language?
• Not in the fullest sense.
• A true language must have productivity –
the capacity to express an infinite number
of novel utterances, right there on the
spot, as circumstances demand
The puzzle of language
development
• How do we learn to talk (sign)?
• Is it through imitation and positive
reinforcement?
• Partially, but not completely.
• Poverty of stimulus – adults do not give
children sufficient instruction to explain
their rapid acquisition of proper language
How do we do it?
• Noam Chomsky, way back in 1957,
claimed that we are all born a mental
module, the language acquisition
device, that is just waiting, as the child
matures, to understand and use universal
grammar
• We are born with a “software” package
that employs primitive grammar and
understands nouns, verbs, negatives, etc.
Evidence supporting Chomsky
• 1) World-wide consistency
• 2) Novel word combinations
• 3) Poor or non-existent adult modeling
• 4) Spontaneous language development
On the other hand ..
• Intense observation of mothers interacting
with infants showed much more interaction
than researchers had anticipated
• The power of positive reinforcement
• Expansions
Evolutionary perspective?
• This amazing facility for language evolved,
through natural selection, because it
helped humans survive and have children
who also survived to have children
• We could, easily and precisely, tell each
other about dangers and opportunities, as
well as cooperate and band together
Physical evidence?
• Genes have been located which
conclusively influence language
development
• Brain structures (left hemisphere) also
have a direct link to language capabilities:
a) Wernicke’s area - comprehension
b) Broca’s area - production
c) Heschl’s gyrus – learning a new
language
But what about behavior?
• Sure, some capacities have developed
through evolutionary processes – we see it
in the brain and genes
• Complex social behaviors though?
• The realm of sociobiology – evolutionary
explanations for social behaviors,
including humans
Sociobiology examples
• Jackal “helpers” – why do they sacrifice
their own reproductive opportunities?
• Mongoose rescues
• Lion infanticide
Humans?
• Can we explain the origins of human
behaviors?
• Junk food obsessions
• Social behaviors?
• Niece/nephew adulation
Better yet, ….
• Do male and female sexual strategies
arise from evolutionary influences?
• Huge controversy
David Buss’ big question
• What do male’s and females look for in a
mate?
• In 37 wildly different countries he found
the same answers
• From Scandinavia to the South Pacific
they were looking for the same thing
Males like …
• Why do women try so hard to look young
and healthy?
• Because those are the qualities that men,
all over the world, select in picking a wife.
• They offer the best chance of producing
the most children.
What women really want
• Why do men, everywhere, strive so hard
for status, dominance and $$?
• Because that is what women look for in a
mate.
• Someone who could provide a stable
home and adequate resources to raise
children.
Other Points
• Evolution is a battle fought by individuals
not species.
• It’s not really, “the survival of the fittest.”
• More accurately, it is. “You must breed to
succeed.”
It takes all kinds
• Evolution explains why we share basic
features and capabilities
• But why are we so different?
• We have inherited differing traits
Heritability
• an estimate of the variance within a
population that is due to genetics
• A measure of nature, excluding nurture
• Ranges from 0 (no genetic influence) to 1
Measuring
heritability
• The heritability of a behavior is estimated
in three ways
• 1) comparing monozygotic (identical) and
diozygotic (fraternal) twins
• 2) looking at identical twins raised in
different households
• 3) seeing whether children more closely
resemble their adoptive or biological
parents
Limits on heritability
• Applies only to a group living in a
particular environment
• Children who face severe malnutrition
might not grow very tall, even if their
parents were giants
IQ and Heritability
• Strong relationship – up to 87% for
identical twins raised together
• Amazingly, the genetic influence grows
even stronger as we age
• Correlations between those adopted and
their adopted family disappear altogether
What about group differences?
• We find consistent differences between
races.
• Are some races genetically inferior?
• Huge controversy
• Long history
• The Bell Jar
Group differences in IQ
Why it’s not the genes
• The Tomato Plant Experiment
• Differing environments lead to different
outcomes
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Expectations
Overlap
Raised elsewhere?
African purity means nothing
The guy you are talking to
• Heritability estimates don’t tell us anything
about an individual, just a large group
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Huge numbers
Big overlap
Tremendous variations in environment
Your genetic blueprint and your
environment are unique
Nature or Nurture
• It is the interaction of our genes and the
environment in which they are expressed
that determine our behavior, experiences
and personality
Genes & behavior
• Researchers have found moderate levels
of heritability for almost all behaviors
• Some genes influence behavior directly
• But often genes influence our behavior
indirectly by giving us advantages or
deficits that have great effect on both what
we do within our environment and how it
responds to us