Download evolution and genetics in psychology

EVOLUTION AND GENETICS
IN PSYCHOLOGY
El
El
El
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Evolutionary Theory
Genetics
Hereditary Transmission
Chromosomes and Chromosomal Abnormalities
Behavior Genetics
Nature and Nurture
4.1. Evolutionary Theory
A. What is evolutionary theory?
1. Evolutionary theory describes the way our bodies and behaviors change across many generations of
individuals. This theory is important because it helps us understand how humans have come to be the way
they are over the course of time since life first appeared on our planet.
2. Charles Darwin proposed in his 1859 book, The Origin of Species, that biological organisms have devel
oped and changed through a mechanism of natural selection, known commonly as “survival of the fittest.”
On this view, species show a great deal of biological variation. At a given time, particular members of a
species will prove to be better able to cope with environmental conditions than will others, and so they will
have an advantage for survival. As a result, they will multiply, and eventually, their progeny will become
more prevalent. They have been selected by nature for survival—hence, the term, “natural selection,”
3.
Scientists often refer to the ability of an organism to cope with the environment as its adaptability. This
term is also sometimes used to refer to the ability of an organism to reproduce its own genes.
4. Those species
whose members are not able to cope with the environment—to adapt—will die off and
perhaps eventually become extinct, meaning that the species will cease to exist.
5.
Darwin believed that the evolution of organisms was gradual. However, recent theorists have suggested
an altemative viewpoint, referred to as punctuated equilibrium. \ccording to this viewpoint, kinds of
organisms remain relatively stable for long periods of time, with such penods of stability punctuated by
relatively brief periods (evolutionarily speaking) of rapid change in kinds of organisms.
B, How does evolutionary theory work?
Natural selection works when environments start to favor certain adaptations to those environments over
others. For example, during the Industrial Revolution in late nineteenth-century England. a particular lightcolored moth was replaced by a dark-colored related moth as the prevalent variety. Why? Industrial pollu
tion had blackened the forests, improving the darker moth’s camouflage against predators such as birds.
The light-colored moth became too visible to predators to survive. Recently. however, with restrictions on
air pollution, the light moth is making a comeback. Thus, natural selection is a constantly shifting process,
intluenLed h\ in or.zanism s hioloy in Intenction stth thc dern inds ot the Ln\lronment
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College Outlinefor Psychology
Ca The evolution of humankind
1. Our own species. IIonzo sapiens. is a member of the biological family of hominids. In general. this
species is distinguished from earlier human-like ones by a number of factors. including physical appearance
and greater development of the brain. In particular, a greater proportion of our behavior is under the voluntary
control of the brain—and thus is selfdirected—than was the case for earlier human-like species.
2. The earliest known horninids. called Horno habilis, h\e(l about 2 million years ago. The brain volume
of Homo habilis was about 450 cubic centimeters (cm
; roughly a pint), in contrast with the volume of the
3
modem human brain. which is roughly I .400 cm (about 1 .5 quarts).
3.
For unknon reasons, another species. Horno erectus, appeared about 1 to 2 million years ago. This
had a much larger brain capacity than did Horno habilis, with a volume of about 950 cm
3 (roughly
a quart). Eventually, this species replaced Horno habilic. The
species spread out more widely than did
the earlier species: Whereas traces of Homo hahilis are limited to Africa. traces of Hoino erectus can be found
on three continents, Eventually, Homo erectus
replaced by Horno 3apien3, our
n species. Later.
another protohuman species. Horno neanderthalis, appeared. hut it is not clear that humans evolved from them.
species
new
was
o
D. Evolution and brain capacity
1. Scientists have been interested in the question of what makes one organism evolutionarih more
“advanced” than another, and some scientists have focused on aspects of brain capacity as a basis for
understanding ad ancement of organisms.
2.
Brain size or weight itself does not provide a good index of intelligence or of any kind of evolutionary
superiority. For example. the Indian elephant has a brain weight almost four times that of humans,
it is
not seen as more advanced intellectually.
yet
3.
A better indicator of intelligence appears to be the relationship between brain weight and total body
weight. As hominids have evolved, their brain weights relative to their total body weights have increased
significantly. But this measure is still imperfect. as shown by the fact that the rodent shrew has a higher ratio
of brain-to-body weight than do humans. It appears that what is most important is the development of a
particular part of the brain, the cerebral cortex, discussed in the next chapter.
4. Comparisons of brain size or weight within species have led to conflicting points of view. Stephen Jay
Gould reported on a study conducted in the nineteenth century that showed that the average weight of the
brains of 119 assassins, murderers, and thieves was ell above the average for the time. He also reported
that the largest female brain e er weighed (1,565 g belonged to a woman who had killed her husband. At
the same
other investigators, such as Richard Lynn, have reported relations between aspects of brain
size and intelligence. The issue thus remains unresolved.
time,
4.2, Genetics
A. Genetics is the stuth of the hereditary
characteristics ia genes. the physiological building
blocks of hereditary transmission. The study
important because it helps us understand one way
in which people develop the psychological, and of course. physical attributes that the express throughout
their lives,
transmission of
of genetics
‘
is
B.
Genetics provides the key to how the evolution of kinds of organisms actually occurs. The mechanism
change
which
when there is a sudden structural change in a hereditar
characteristic that is not predictable from the
of the parent. Mutations can be caused bx a ariet
things, including chemical substances and s arious types of electromagnetic
for
genetic
is
mutation,
occurs
genes
of
radiation,
C. Genetics also provides part of the key to understanding how we come to be who we are. Genetic
mission leads to the formation of biological traits. ‘a hich are distinctix e characteristics or heha ior patterns
that are genetically determined. All organisms receive their genes, and hence the capacity to develop certain
biological traits, at the time of conception.
trans
D.
Modem genetic theory dates hack to the research of an Austrian monk and botanist. Gregor Menclel
(l822—lS84. who perlormed breeding experiments on common sarieties of the garden pea. Mendel
surmised that certain inherited attributes are
than others. The stronger attributes are referred to as
dommant traits and the ‘a eaker ones as recessi e traits.
stronger
Evolution and Genetics in Psychology
37
4.3. Hereditary Transmission
A.
Mende1s ohervation of stronger and \\eaker attributes resulted from his ork it1i pea plants.
1 ). Nlendel observed that if true-breeding tall pea plants ones that al a s produce tall offspring ) are
crossed ith true—breeding dwarf pea plants ones that al a s produce small oltspring the offspring
of the tall and the dwarf plants ill al\\ a\ s he tail. Thus. tallness is a dominant trait and dwarfism a
recessi e trait.
.
If one interhreeds all of the tall members of the first generation of offspring. the second generation
of offspring ill not all be tall. Rather. there i11 be both fall and short plants. in a ratio Of about tlwee tall
plants to e er’v one short plant. What mechanism could account for the difference in the offspring of all tall
parents in the two generations?
2).
B. The
mechanism is controlled by the laws of hereditary transmission. To make the example simple.
suppose that the height of a plant is controlled by exactly two genes (building blocks of heredity, mentioned
above), one of which comes from each parent and forms each half of a gene pair. Both inherited genes may
be for tallness, both may be for dwarfism, or one may be for tallness and one for dwarfism, If we represent
tallness by T and dwarfism by d, then the possible inherited gene combinations, \\hich are each referred to
as a genotype, are TI; Td, dT and dd, for the height of plants.
C. The law of dominance states that whenever a dominant gene is paired with a recessive gene. even though
both genes are present. the observable result in an organism-—the phenotype—u ill he that of the dominant
trait. Thus, any plant that has as its genotype TI; Ti, or dT will show up as taIl. shereas only a plant ‘.s ith a
dd genotype will he phenotpicall\ short.
D. We can nos understand hy. in the tsso generations. Mendel’s plants had different distributions of
phenotypes. In the parent generation, plants were either TTor dd. They were thus pure-breeding. When these
two types of plants were crossed, the offspring were all hybrids, meaning that they all had mixed genotypes:
Td and dT All would show up as tall because the dominant genotype prevailed in the phenotype. In the
second generation of offspring, the genotypes were equally matched among Td, TI; dd, and dT (the four
possible permutations of Td with dl). The Td, TI; and dT plants showed up as tall, the dd ones as short—
hence, the 3:1 ratio of tall to short plants.
E.
In humans, the expression of a single genotype can give rise to a range of phenotypes, because heredi
tary transmission is almost never as simple as in the aboe example. Consider the example of height in
humans. A person’s height is largely’ genetically controlled. But other factors, such as nutrition, hormones.
and immune-system deficiency. can affect the height a person achieves. Moreover, genetic transmission
itself is complicated by many factors. Thus, even traits that are highly heritable (genetically based and
passed from generation to generation) are not completely controlled by simple laws of genetics.
4.4. Chromosomes and Chromosomal Abnormalities
A. The genes
that are responsible fur hereditary transmission are themsels Cs parts of chromosomes, u hich
are rod-shaped bodies containing very large numbers of the genes. Humans has e 23 pairs of chromosomes.
for a total of 46 in all, although the number of chromosomes differs from one species to another. One of each
pair of chromosomes was received at conception from the mother, and the other from the father, so that half
of each individual’s heredity can be traced to each parent.
B. The genetic material of which chromosomes are composed is deoxyribonucleic acid, also known as DNA.
C. Chromosomes gosern many aspects of a person. including eye color and blood type. as well as sex. In
psychology. we distinguish between a person’s sex, or ph\ siological characteristic of being male or female.
and the person’s gender, or psscholorical identification as being male or female. For most people. although
not es cry one. sex and gender identification correspond.
D. Two
specific chromosomes are crucial in determining sex: the X and Y chromosomes, Females
receis e an X chromosome from both parents. and thus has e XX pairin of their sex-determinatis e
chromosomes. Males receis e an X chromosome from their moiheN and a ‘1 chromosome from their
fathers, resulting in their having an XV pairing of the sex-determinatis e chromosomes. Although the
overwhelming majority of people have either the XX or XY pairing on the last chromosome, occasional
abnormalities occur,
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College Outlinefor Psychology
E. Some people receive just a single X chromosome. and nothing more. They have Turner’s syndrome,
which occurs in roughly 1 of every 3,000 live female births. People with this syndrome are female but are
sexually underdeveloped. They are typically short, and their necks have a webbed appearance. Some
psychological research has shown that Turner’s syndrome patients typically show decreased ability to
perceive spatial organization.
F. Some males receive an
X chromosome, and thus their chromosome code is XXY. These individuals
exhibit Klinefelter’s syndrome, which occurs in roughly 1 or 2 per 1,000 live births, The individuals are
male, but with underdeveloped testes and secondary male sexual characteristics, such as facial hair. They
are also infertile (unable to produce offspring). About half of the individuals are mentally retarded.
extra
G. Yet another syndrome is XYY syndrome, sometimes called the “Supermale syndrome,” in which a
male is born with an
Y chromosome. This syndrome occurs in roughly I of every 1,000 live births.
XYY males are likely to be taller than average and typically test lower than normal on intelligence tests.
There is also some evidence of increased aggressiveness. Some psychological investigators have suggested
an association between XYY syndrome and criminality, but this association remains unproved.
extra
4.5. Behavior Genetics
A. Behavior genetics is the study of how psychological attributes, including behavior, are passed
genetically.
on
B. The contribution of heredity to various psychological attributes is often expressed in terms of a
heritability coefficient, a number on a scale from 0 to 1 that expresses the proportion of the variation among
individuals that is alleged to be due to heredity. It is important to remember that the coefficient indicates vari
ation in an attribute. In other words, the coefficient is affected by the amount of variation in the attribute in the
population being studied. Were there no variation, there could be no meaningful estimation of heritability.
C. Several different methods are used to estimate heritability. The three most widely used methods are
based on separated identical twins reared apart, identical versus fraternal twins, and adoption.
1). In the method of identical twins reared apart, use is made of the fact that identical twins have
identical genes. If two identical twins are separated at (or. at least, near) birth, then any differences between
them must be due to environment. By studying a number of such twin pairs. it is possible to estimate heri
tability of various attributes, In using this method, one must ensure that the twins were truly separated early,
and that their environments were truly independent (not, for example, that one twin was raised by the par
ents and the other by a family member such as a sister).
2). In the method of identical versus fraternal twins, use is made of the fact that whereas identical
twins share all their genes, fraternal twins share only half. By comparing the similarities of identical versus
fraternal
attributes, it is possible to estimate heritability. Note that this method assumes that iden
tical and fraternal twins share environments to an equal degree. an assumption that may be questionable if
identical twins are brought up in more similar environments than fraternal ones. solely by virtue of their
being identical twins,
twins on
3). In the method of adoption, one compares the similarity of biological children and adoptive chil
dren to their parents. Such studies require use of families in which there are both natural-horn and adoptive
children. In such a study, one starts with the fact that the natural-born children will have received all their
genes from their parents, whereas the adoptive children will have received none of their
the par
ents with whom they are living. Note that this method
that natural-born and adoptive children share
comparable environments, an assumption that may not always be met.
genes from
assumes
4.6. Nature and Nurture
A. Just as peas follow a certain pattern of genetic transmission, so do all living organisms. Some people
have taken advantage of this fact in attempts to introduce selective breeding, or the purposeful mating of
organisms with each other in order to encourage certain biological traits or to discourage others. For
example, selective breeding is used in the mating of many race horses in an attempt to produce racewinning
horses in subsequent generations.
certain
Evolution and Genetics in Psychology
39
Robert Tryon. in an experiment done in I Q4O investigated the results of sehctive breeding in a strain of
rats. \arious rats cre tested for their ability to run a maze and then were bred in successive generations to
he brighter or less bright, as assessed by their ability to run the maze. Results were mixed. On the one hand.
it was possible to breed maze-bright and maie—dull rats. on the other hand. the rats abilities turned out to
be extremely specific. Even small changes in the nature of the maze eliminated the significant difference in
maze-running ability betsseen the groups.
B
c*
In the nineteenth centur. a mosement arose that argued for selective breeding in humans. This rnove
ment. called the eugenics movement, was motix ated h the belief that the world ssould be a better place if
people who were more genetically fit were encouraged to reproduce. whereas those who were genetically
less fit were discouraged from reproduction. Because there is no clear definition of what makes one person
more genetically fit than another, nor any clear ethical basis for making such decisions for other people. the
movement has never gained uni\ersal popularlt\.
A school of thought related to the eugenics movement was social Darwinism. championed by
Herbert Spencer. Spencer and others proposed that the concept of survival of the fittest could be applied
to social status, such that people who achiesed more in their lives (e.g., greater incomes or social stand
ing) could be iewed as sociall\ the most fit. This mo ement floundered in large part because it could
he used to justify any existing socioeconomic hierarchy at all. no matter how unfair or even unjust it
happened to he.
D.
‘
E. In modem times, a movement of sociohiology has sprung up. led by Edward Wilson, among others. This
movement seeks to understand human behavior in terms of evolutionary principles. For example, observed
differences between male and female behavior might be attributed to different selective pressures on males
and females as they evolved. It is sometimes hard to disconfirm sociobiological explanations. as they are all
necessarily after the fact rather than predictive.
identities is sometimes called
human adaptability through
to
increase
the euthenics movement, Followers of this movement have sought
still try to improve
people
today,
environmental change. Although we rarely use the term “euthenics”
potential.
environments for the young in order to let them develop to their full
F. An alternative movement that has continued for many years under various
-
,—
1. Darwin’s view of natural selection holds that organisms tend to survive and reproduce as a func
tion of their ability to adapt to the environment, with less adaptable kinds of organisms diminishing
and, often, eventually becoming extinct.
2. A mutation occurs when the genetic message that would normally he passed on from parents to
offspring is altered. resulting in a new organism with a genetic code not predictable from the genetic
material of the parents. This mechanism for natural selection was not understood before Darwin
proposed his re oluti onarv theory.
3. Species that we vie as more intelligent are generally characterized by greater brain-to-body weight.
Within a species. however, there is no solid evidence that brain weight corresponds to intelligence.
3. Punctuated equilibrium refers to the view that evolutionary change proceeds in bursts rather than
in smooth, gradual transitions,
5. Genes are the biological units that contribute to the hereditary transmission of biological traits, that
is. inherited characteristics, Genes are located on chromosomes, which come in pairs. Humans have
23 such pairs. the23rd of which is responsible for determining sex.
6. Females have an XX chromosome pairing. males, an XY pairing.
7. Various sex—linked chromosomal abnormalities have been identified, Some of the main ones are
Turner’s syndrome, associated with a single X chromosome; Klinefelter’s syndrome, associated
with an XXY chromosome combination; and XYY syndrome.
S. A genotype is the genetic code for a trait. A phenotype is the actual ‘.isible expression of the trait
in offspring. A gi’en genotype can produce a variety of phenotpes.
40
college Outline for Psychology
9. Behavior genetics is the study of the transmission of behavior (and other psychological character
istics) through the genes.
10. The coefficient of heritability is a number on a 0-to-I scale that indicates the proportion of
variation in a population attribute that is due to hereditary influence.
11. Three of the main methods used to estimate coefficients of heritability are the methods of identical
twins raised apart, identical versus fraternal twins, and adoption.
12. Two movements that have attempted to apply principles of natural selection to behavior are social
Darwinism and sociobiology. The former movement is now discredited, because it could be and was
used to justify virtually any existing social order, The latter movement is active today in the attempt to
understand how people’s current behavior can be understood as constituting an evolutionary adaptation.
13. Selective breeding has been performed Lo produce animals with particular characteristics, such
as in the breeding of race horses. The eugenics movement attempted to apply the philosophy of
selective breeding to humans. The euthenics movement seeks to improve humankind through envi
ronmental manipulations.
adaptability
behavior genetics
biological trait
chromosome
deoxyribonucleic acid
DNA
dominant trait
eugenics movement
euthenics movement
evolutionary theory
extinct
gender
gene
genetics
genotype
heritability coefficient
heritable
hominid
Jlonio erectus
Horno habilis
Homo neanderthalis
Horno sapiens
hybrid
Klinefelter’s syndrome
method of adoption
method of identical twins
reared apart
method of identical versus
fraternal twins
mutation
natural selection
phenotype
punctuated equilibrium
recessive trait
selective breeding
sex
social Darwinism
sociobiology
Supermale syndrome
Turner’s syndrome
XX
XY
XYY syndrome
A. Select the best response option from among the four that are given.
1.
Of the following,
is the best indicator of evolutionary advancement.
A. ratio of brain-to-body weight
B. brain capacity
C. amount of cerebral cortex
D. chronological age
2.
In the method of
a researcher compares natural-born children to nonhiological children
under the same environmental conditions.
A. identical twins reared apart
B. identical versus fraternal twins
C. heritability
D. adoption
,
3.
A.
B.
C.
D.
is the study of the hereditary transmission of attributes via
Heritability, biological traits
Genetics, genes
Adaptability, dominant and recessive traits
Mutation, differentiation
________
_______
________
Evolution and Genetics in Psychology
41
4. A male born with an extra Y chromosome. XYY, sometimes referred to as
shows sonic
evidence of increased aggressiveness and typically scores lower than normal on intelligence tests.
A. Turner’s syndrome
B. Supermale syndrome
C. XXX syndrome
D. Klinefelter’s syndrome
5. The
A.
B.
C.
D.
B.
material of which chromosomes are composed is called
deoxyribonucleic acid
genes
atoms
mvelin
Answer each of the following questions with the appropriate word or phrase.
6.
is a way of understanding how species change through time.
7. An unpredictable change or
characteristic.
occurs when there is a structural change in a hereditary
8. Behavior genetics attempts to explain how behavior is passed along through generations via
9. Genes are located on
which are composed of
10. The total number of pairs of chromosomes in a normal human is
11. The
constitutes the observable characteristics of an organism, while the
consti
tutes the characteristics that an individual has inherited and will transmit to his or her descendants.
12. An individual whose sex chromosome pairing is XX is biologically
13.
C.
is the theory that evolution is not a gradual process, but rather proceeds in small bursts.
Answer T (true) or F (false) to each of the following statements.
14. An organism with a higher brain weight is always more evolutionarily advanced than is one with
a lower brain weight.
15. Homo habilis had a greater brain capacity than did flomo erectus.
16. A heritability coefficient indicates the proportion of variability of a characteristic that is due to
heredity.
17. Recessive traits are traits that are never manifested in an organism.
18. Euthenics is concerned with the improvement of society through improved adaptability and envi
ronmental change.
19. Eugenicists believe that societal improvement is best sought through selective genetic engineering.
20. The method of identical versus fraternal twins estimates heritability by measurinT the extent to
which environmental variables influence the behavior of genetically identical individuals.
21. A heritabilit coefficient of 1.5 indicates a high degree of heritability.
22. Modern genetic theory started with the work of Gregor Mendel, who studied the heritability of
certain attributes of pea plants.
11