Human development and bechavior

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Transcript Human development and bechavior

Human development and
The study of human development
• The study of human development concerns
the ways in which people change with the
passage of time. It emphasizes a pattern of
changes throughout the life span, often in
three broad areas: physical, social, and
• We consider each of these areas and then an
issue underlying all of them: the influences of
heredity and environment.
Biological Influences
• The behavior of these children was partly a function of
their genetic endowment and, like all of us, each child
began life in a very small way, as a single cell. This fertilized
cell, resulting from the union of the father's sperm and the
mother's egg, is but half the size of the dot over this "i," yet
all of the inborn influences on our physical, mental, and
even social development are set at this miraculous moment
of conception.
• As we leave these infants to consider the structures and
processes behind all of our origins, we must realize that no
further hereditary influences are possible during the rest of
our lives. Our entire heredity, the sum of characteristics
and potentialities biologically transmitted from our parents,
is contained in this one fertilized cell.
Chromosomes and Genes
• One pair consists of the sex chromosomes, X and Y,
which result in the development of a male or female.
The male is XY, receiving an X from the mother and a
Ffrom the father, whereas the female receives an X
from each parent. The two little girls each had an XX
• Within the chromosomes are even more fundamental
determiners of heredity, called genes, which contain
the basic blueprint that specifically directs the
development of most physical characteristics and
certain behavioral traits.
During prenatal life
• During prenatal life, as the first cell
successively multiplies, the complete genetic
code is passed on to each of the resulting
• All cells in the human body thus contain the
same inheritance with one exception, the
reproductive cells.
The reproductive cells
• Beginning in puberty, when the reproductive cells
first appear, cell division occurs in such a way that
the sperm in the male and the egg in the female
receive only one member of each pair of
• The chromosomes contain only one-half of the
individual's full genetic code; furthermore, the
different eggs or sperms produced by the same
individual receive different sets of chromosomes
with their countless thousands of genes.
Single-pair Traits
• The physical features of the two orphan girls were
determined by a particular assortment of genes.
• Perhaps one of the girls had brown eyes and, since
genes come in pairs, let us refer to these genes as BB.
The capital В is used because the gene for brown eyes
is a dominant gene, meaning that it takes precedence,
suppressing the influence of its counterpart. The other
child might have a Bb, and it would also be brown-eyed
because of the dominant B. Still another child might
have bb.
Multiple-pair Traits
• It is speculated that multiple pairs of genes involve two
degrees of expression but no dominance. One pair
might be expressed as A and a, another as В and b, and
so on for as many genes as are relevant. A rat with AA
is brighter than aa, and a rat with Aa falls between the
two. Similarly, BB is brighter than Bb which, in turn, is
brighter than bb.
• Since it is assumed that no dominance exists in the
gene pairs, the brightest rat would be AABBCCDD, the
dullest aabbccdd, and the intermediate levels would be
AaBbCcDd, aAbbCCDd, and so forth.
Concept of Imprinting
• Under normal circumstances, for example, newborn
ducklings and goslings follow their mother soon after
hatching, perhaps because they are stimulated initially by
her movements or vocalizations. This learned attachment
of young animals to members of their own species is called
imprinting, and there is nothing extraordinary about this
following behavior except that it is acquired during a
certain optimal time for learning.
• This period varies for different species, but in geese it
occurs up to sixteen hours after birth, after which readiness
to learn to follow declines rapidly. The young bird is so
ready during this initial period that this following behavior
can be elicited by almost any perceptible object that
moves, living or inanimate.
• Many researchers believe
that there is an important
early period for human
social responsiveness, but
they do not speculate in
regard to the exact interval.
It is probably unwise to
assume a critical period
when there may be different
periods for different
• The first three days after
birth, for example, may be
sufficient for initiating infant
bonding to the mother's
voice. Some investigators
speak of a sensitive period,
implying its importance but
not its irreversibility.
Heredity and environment
• The tests administered to the transferred children before
their departure had been administered routinely to all the
children in the orphanage. On this basis a useful research
study could be designed.
• It would be possible to identify a comparable
nontransferred group, and for this purpose he selected 12
children with an average age of 17 months and an average
IQ of 87.
• The chief factor accounting for this difference, according to
Skeels, was the amount of stimulation and adult-child
interaction for the transferred children. Their rapid and
positive physical, social, and cognitive changes suggested
that environmental conditions can play a significant role in
the developmental process.
Nature-Nurture Issue
• Each of us is a product of both heredity and
environment, but are two individuals different
because of their heredity or because of their
• Sir Francis Galton called this question the
nature-nurture issue, referring to the
influences of heredity and environment,
respectively, and he thereby called further
attention to a long-standing controversy.
Studies with Animals
• The most precise demonstrations of heredityenvironment relationships are found in animal studies
because here even the most basic environmental
factors can be readily controlled. The development of
swimming in tadpoles, flying in pigeons, and sexual
behavior among monkeys all have been studied in this
• Series of experiments with infant monkeys also showed
that extreme environments can alter the potential
influences of heredity. Monkeys that do not receive the
usual maternal stimulation and affection during infancy
fail to develop into normal adults. Their social
relationships are infrequent or ineffective.
Identical Twins
• At the human level nature has provided us with some
help in assessing these influences. Heredity in fraternal
twins is no more similar than between any other pair
of siblings, but in identical twins heredity is exactly the
• When these twins were brought together and
compared, they were found to be much alike in
physical characteristics and appearance.
• Differences in educational opportunity can produce
significant differences in intelligence. Finally, in
personality traits the separately reared twins were
sometimes similar and sometimes very different.
Twins in different age
Interaction Principle
• Through such investigations it is now apparent
that the heredity-environment question is not an
either-or matter. The contributions of both
factors are widely acknowledged, and the main
focus of contemporary research is on discovering
the ways in which they combine to bring about a
given characteristic.
• The current concern is with the relationships
between these two sets of factors, an interplay of
forces that can be extremely complex and
Concept of Readiness
• Readiness is the time at which
an organism is first
physiologically capable of
responding properly in a given
situation. The degree of
preparedness to act or respond
to a particular stimulus. 2. The
level of preparation for a given
task sufficient to result in
meaningful learning.
• With different instructional
opportunities, children are
ready to learn two and three
years earlier and, of course,
Readiness for school
• Six and a half years was
the average mental age
of readiness for reading
as it was then taught in
the schools.
Individual differences
• These differences might involve physical,
social, cognitive, or other characteristics.
• Psychologists sometimes study the ways in
which people are alike, which can be part of
developmental psychology, and sometimes
they focus on the ways in which we differ,
called the psychology of individual differences.
Developmental changes in the life
• The most rapid
developmental changes
in the life span take
place in childhood.
According to Erikson's
theory, they concern the
development of trust,
autonomy, initiative, and
• If these issues are not
resolved in the early
years, they are difficult
to resolve later.
Developmental changes in the life
• A second period of rapid
development occurs during
adolescence, when
hormonal secretions
produce physiological
changes having
repercussions for physical,
social, emotional, and
sexual life, as well as
• The most significant
psychosocial issue at this
stage is that of establishing
a personal identity.
Developmental changes in the life
• Healthy adults,
according to Erikson,
can find satisfaction
in relations with
• The psychosocial
issues in adulthood
involve intimacy,
which occurs with
another person, and
generativity, which
concerns future
• Heritability describes the extent to which variation
among members of a group can be attributed to genes.
Heritable individual differences in traits such as height
or intelligence need not explain group differences.
• Genes mostly explain why some are taller than others,
but not why people today are taller than a century ago.
• Developmental psychology is concerned with studying
the shape of within-person change in central domains
of functioning across the entire human life span. Of
particular relevance is the identification of antecedent
conditions, correlates, and consequences of those
trajectories as well as their interrelations and
Evolutionary psychology
• Evolutionary psychologists seek to understand how
natural selection has shaped our traits and behavior
tendencies. The principle of natural selection states
that variations increasing the odds of reproducing and
surviving are most likely to be passed on to future
• Some variations arise from mutations (random errors
in gene replication), others from new gene
combinations at conception. Charles Darwin, whose
theory of evolution has for a long time been an
organizing principle in biology, anticipated the
contemporary application of evolutionary principles in
• Evolutionary psychology basically attempts to
explain human psychology in terms of
adaptive evolutionary principles.