Genes and behavior
Our genes, cells, anatomy and physiological processes are similar to the animals indicating
common descent. It would be a wonder if it were not true for our behavior. However, there is
no consensus concerning the relative importance of an individual's innate qualities ("nature")
versus personal experiences ("nurture") in determining our behavioral traits.
SLIDE 1 Schools of psychological thought
1. Freud’s psychoanalytic theory Freud is best known for his redefinition of sexual desire as the primary
motivational energy of human life, as well as his therapeutic techniques, including the use of free association,
and the interpretation of dreams as sources of insight into unconscious desires. His theory was shocking at the
Victorian time. He assumed two groups instincts: (a) life-saving instincts (need for air, food, fear from snakes,
etc.); and (b) sexual instincts. Note that these categories fit very well to Darwin’s survival and sexual selection
theories.
2. William James, similarly to Freud, built his theory on instincts. He believed that instincts are of evolutionary
origin, and that, contrary to the common belief, human has more instincts than animals.
3. Behaviorism Ivan P. Pavlov and James B. Watson (not the discoverer of DNA structure!), instead of instincts,
emphasized the importance of learning. They claimed that instincts are not important, the brain is a blank slate.
They used the so called operational conditioning technique where they bound two independent stimuli: e.g. the
sound of a bell and the salivation. After some practice, ringing itself (without the presence of food) could evoke
salivation in dogs. Behaviorist thought that this scheme (binding two independent stimuli) is the very basis of
leaning. The radical school of behaviorism, represented by Burrhus Skinner maintained that behaviors as such
can be described scientifically without recourse either to internal physiological events or to hypothetical
constructs such as the mind. In other words, they considered the brain as a black box, and did not care what
happens inside. They only investigated the output response for a specific input.
4. The cognitive psychology rejected the black box concept of brain proposed by behaviorism. This school, using psychological methods,- examines what within the brain happen. The scope of the investigation by
cognitive psychology involves problem solving, memory, language, etc.
SLIDE 2 Sociology In contrast to psychology, sociology investigates human behavior in groups and in
different cultures. Social psychology also investigates group behavior using psychological methods, beside
sociology.
SLIDE 3, 4 Schools of biological thought
1. The ethology movement arose to counterbalance environmentalism, which was a popular school in the USA
emphasizing the primacy of environment on the determination of behavior. Ethology claims that instincts play a
vital role in behavior. Konrad Lorenz, the most famous ethologist observed that young geese accept the first
moving object as mother, and he called this phenomenon as imprinting.
2. Sociobiology attempts to explain human behavior on the basis of evolutionary benefits. Sociobiology
introduced the concept of kin selection, which means that helping the relatives is an evolutionary tool for
spreading of our genes since we have common genes with our relatives.
3. Evolutionary psychology explains the origin of human behavior by evolutionary mechanisms. Its principles
are as follows: (1) evolution formed not only our body but also our mind; (2) these features, despite differences
on the surface, are universal in every human societies; (3) human behavior is encoded in separate modules in the
brain.
SLIDE 5 Twin studies and behavior Twin studies aid the study of individual differences by
highlighting the role of environmental and genetic causes on behavior. Twins are invaluable
for studying these important questions because they disentangle the sharing of genes and
environments. If we observe that children in a family are more similar than might be expected
by chance, this may reflect shared environmental influences common to members of family 1
class, parenting styles, education etc. - but they will also reflect shared genes, inherited from
parents. The twin design compares the similarity of identical twins who share 100% of their
genes, to that of dizygotic or fraternal twins, who share only 50% of their genes. By studying
many hundreds of families of twins, researchers can then understand more about the role of
genetic effects, and the effects of shared and unique environment effects. Modern twin studies
have shown that almost all traits are in part influenced by genetic differences, with some
characteristics showing a strong influence (e.g. height), others an intermediate level (e.g. IQ)
and some more complex heritabilities, with evidence for different genes affecting different
elements of the trait - for instance autism. The differences can be explained by environmental
or epigenetic effects, which are not necessarily mutually exclusive.
SLIDE 6 One gene, one behavior paradigm is based on the misconception that there is a
one-to-one relationship between a gene and a complex behavior. This concept is easier to
digest by public media and it is easier to investigate.
SLIDE 7, 8 The gene of faithfulness and ruthlessness (AVPR1a gene) A genetic screen for
marital success? A Canadian company is actually offering just that sort of test. For $99,
Genesis Biolabs will examine your - or your partner’s - vasopressin 1a receptor (AVPR1a)
gene, which this year grabbed headlines once as the “ruthlessness gene” and again as a
“divorce gene.” Vasopressin is a hormone involved in attachment to mates and offspring.
Among voles, prairie voles are true to their mates. Meadow and montane voles prefer to play
the field. Prairie voles have a few extra bases in the DNA in front of this gene, which
influences how much and where vasopressin is released in the brain. This difference matters:
Extra AVPR1a in the brain makes promiscuous meadow voles act more like monogamous
prairie voles, spending more time with partners and grooming offspring. Scientists have now
observed hints that variation in the human AVPR1a gene may influence the far more complex
arena of human behavior. A research team looked at the DNA preceding the AVPR1a gene in
about 500 pairs of adult same-sex Swedish twins, all of them married or cohabiting for at least
5 years, and their partners. One short variant of a stretch of DNA in this region - there are
several variants - was associated with less stable relationships. Answers to questions such as
“How often do you kiss your mate?” and “How often are you and your partner involved in
common interests outside the family?” reflected slightly lower feelings of attachment on the
part of men with this variant, researchers reported in high prestigious journal. These men were
less likely to be married and, among those in relationships, more likely to have experienced
recent marital strife. A gene worth testing to be assured of marital bliss? Not quite. This is a
brand-new study for which replication has not been attempted. Another paper showed a
different link between AVPR1a and how people treat others. It has been reported that the
length of the variant predicted how human subjects would respond in the “dictator game,” a
way to assess altruism. The researchers divided 200 volunteers into groups “A” and “B.” The
“A’s” received $14 each and were told to share as much as they wished with a “B” whom
they had never met. About 18% kept all the money, and 6% gave it all away, with the rest
somewhere in the middle. The people who behaved more selfishly - or, as the headlines
proclaimed, more ruthlessly - had the same variant as the people with the less stable
relationships. It can be speculated that in these people, vasopressin receptors were distributed
in such a way that they provided less of a sense of reward from the act of giving (or loving).
Scientists suspect that short variants of this gene will be implicated in autism and related
disorders, because a core feature of autism is the inability to make connections with other
people. Although such theories are intellectually appealing, there are few replicated studies to
give them heft. Too often, the subjects assessed are too different - How does one compare
adolescents with married couples? - and the effect of environment too difficult to control for.
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So, getting reliable replications of studies involving behavior is “much harder than for studies
of medical conditions.”
SLIDE 9-11 The warrior gene (MAO-A gene) In 2006 a political storm was stirred up when
it was reported that a variant of a gene for monoamine oxidase-A (MAO-A) - which breaks
down neurotransmitters - could be behind risk-taking and aggressive behavior in Maori, the
indigenous people of New Zealand. The Maori have a warlike heritage, and a large proportion
of this ethnic group carry a version of the gene shown in animal studies to be connected to
aggressive behavior. It has been suggested that the gene could help explain Maori social and
health problems such as fighting, gambling, and addictions. Although it’s true that 60% of
Asians (including Maori) carry the “warrior” variant (compared with 40% of Caucasians), the
critics quickly pointed out that it was too big a leap to ascribe Maori social problems to a
single gene. Yet brain-imaging studies “underscore the role of MAO-A [quite] specifically” in
male aggressiveness, researchers have not detected connections between brain MAO-A and
any other personality trait, she notes. In one study using functional magnetic resonance (MRI)
imaging, investigators presented normal subjects with neutral or “emotionally aversive”
images such as fearful faces. Monitoring activity in key brain regions such as the amygdale
(the brain center for emotions), the seat of fear, they found that the amygdalas of subjects with
the “warrior” variant were hyper-responsive to such images. This sensitivity suggests that
these individuals had problems regulating their emotions, which would also make them more
likely to act on aggressive impulses. But the gene variant isn’t all that matters. It has been
shown by another group that the environment - in the form of traumatic life events - plays a
critical role in how this gene is expressed. Another researchers group reported that the warrior
MAOA variant is associated with violent and antisocial behavior but only in people with a
history of abuse as children. These men were 2.8 times as likely as nonabused males with this
genotype to develop behavioral problems that are often the precursor to a life of crime and
drug abuse. Children with a different variant were less likely to develop antisocial problems in
response to maltreatment. Testosterone seems to add toxicity to the mix. It was reported that
the combination of low MAO-A and high testosterone spells antisocial behavior, as revealed
by answers on an aggression scale. Maybe the hormone causes trouble only in males who also
have this gene variant. The warrior gene as the root of social ills may be dead, but it still has a
fighting chance as a gene important to behavior.
SLIDE 12 The gene of intelligence (CHRM2 gene) It has been recently reported that certain
aspects of IQ seemed to be related to CHRM2 (cholinergic muscarinic 2 receptor), a gene
whose protein is involved in pathways related to learning, memory, and problem-solving.
There, a research team analyzed DNA and IQ test results from members of 200 families, 2150
individuals in all, as part of the Collaborative Study on the Genetics of Alcoholism. The team
found a modest correlation between spatial and logical reasoning skills and certain variations
in this gene. But this study is one of very few to find any connection between genes and IQ and it has yet to be replicated. This situation reflects a major paradox. Cognitive abilities are
among the most genetically influenced of human behavioral traits: In studies over the years,
scientists have estimated that somewhere between 40% to 80% of the variation in individual
IQ scores in a given population is attributable to individual genetic differences. This is
comparable to the genetic influence on height. Yet IQ genes have so far been impossible to
nail down. The largest study yet was a genome-wide scan of DNA from 6000 children using
500,000 markers that could help pinpoint relevant DNA. The study compared groups of lowIQ children with groups of high-IQ children in hopes of teasing out markers linked to
intelligence. A handful of markers had a significant association with the aspects of IQ deemed
most heritable, such as verbal ability. But none accounted for more than 0.4% of the variance.
In other words, if the IQs of the population in question ranged from 80 to130 points, the
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biggest gene effect the researchers could find would account for less than one-quarter of an IQ
point. It seems to be much easier to identify genes for disabilities than for abilities.
SLIDE 13 The gene of addiction (dopamine D2 receptor gene) What do Amy Winehouse,
and Jimmy Hendrix have in common? If you want to find examples of people whose brain
reward circuits have gone haywire, the world of rock stars is probably a good place to look.
But is a dopamine receptor gene at the heart of these musicians’ addictions? Scientists have
proposed that deficiencies in the brain messenger dopamine lead to various unhealthy forms
of sensation-seeking to compensate for the failure to get a charge out of things that give most
people pleasure. For years, they’ve been trying to nail down the role of dopamine receptors, in
particular one called the D2 dopamine receptor, in addictions to alcohol, drugs, smoking, or
gambling, as well as eating disorders and obesity. The A1 allele of this gene yields receptors
that don’t work as well, and that translates into less dopamine firing up the reward circuits.
Some scientists think this can lead to a tendency to abuse drugs and engage in impulsive,
sensation-seeking, or antisocial behavior - including problems forming relationships.
Scientists reported that in a group of 195 student subjects those with A1 alleles were more
likely to engage in early sexual activity but were less inclined to develop steady relationships.
This putative role in attachment has attracted the attention of political scientists looking for
possible biological foundations for political behavior. There is a suggestion for a connection
between low dopamine receptor binding and low social bonding. They hypothesized that
people with more efficient receptors - that is, with one or more A2 alleles - would be more
trusting and, therefore more likely to join a political party. Indeed, people with two A2 alleles
(and no A1) were 8% more likely to form political attachments. But that’s only the latest in
the long and contradiction-riddled history of research on the D2 dopamine receptor gene. It
was found that boys with one A1 allele tended to have higher delinquency rates than those
with two copies of the A2 allele. But the rates were also higher than in those boys with two
A1 copies, suggesting that there is not a simple relationship between the amount of dopamine
and behavior. So, there is still more heat than light with this gene.
SLIDE 14 The gene of religious belief (VMAT2 gene) The VMAT2 gene codes for a vesicular monoamine
transporter that plays a key role in regulating the levels of the brain chemicals serotonin, dopamine and
norepinephrine. Specifically, VMAT2 is an integral membrane protein that acts to transport monoamines from
cellular cytosol into synaptic vesicle. According to this hypothesis, the God gene is not an encoding for the belief
in God itself but a physiological arrangement that produces the sensations associated, by some, with the presence
of God or other mystic experiences, or more specifically spirituality as a state of mind.
SLIDE 15 The gene of homosexuality (Xq28 region) The scientific findings began with
finding subtle differences in the post-mortem brains of heterosexual and homosexual young
men. The cluster of neurons known as INAH 3 in the hypothalamus were reduced in size in
homosexual men, much to the same degree that the same group of neurons is reduced in
women. This region of the hypothalamus is also commonly thought of as participating in “the
regulation of male-typical sexual behavior” Later it has been reported that, using DNA from
homosexual siblings and their pedigrees, a gene for homosexuality seemed to be maternally
linked and found on the Xq28 stretch of the X chromosome. It was claimed that the linkage
translated to a “99.5% certainty that there is a gene (or genes) in this area of the X
chromosome that predisposes a male to become a heterosexual”. There has been no
independent confirmation of the existence of a "gay gene" and today there is considerable
doubt about its existence.
SLIDE 16 The gene of speech (FOXP2 gene) A severe problem in speech was discovered in a family in
England. The members of the family have two seemingly independent problems: difficulties in articulation and
using grammar appropriately. Genetic investigations revealed that the FoxP2 gene was inactivated by a mutation
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in this family. FoxP2 gene is an evolutionarily very conserved gene differing in a single amino acid between
chimp and mouse, but there are two amino acids difference between chimp and human.
The grb10 gene, the gene of dominance (DIA 26) All animals have two copies of each gene:
one inherited from each parent. For most genes, both copies are active, but for some genes,
one copy is switched off – a process called imprinting. Scientists have found (2011) that a
gene called Grb10 has both copies active but the copy from the father is only active in the
brain, whilst the maternal copy is active in all other parts of the body. The study, published in
the prestigious journal Nature, has shown that the two copies actually drive very different
processes: the maternal copy is involved in fetal growth, metabolism and fat storage, whereas
the paternal one regulates social behavior in adults. To confirm this, the researchers studied
the behavior of mice that lacked a copy of Grb10 from their father i.e. the gene was not active
in the brain and worked normally in the rest of the body. They found that these mice were
more domineering, over-grooming their companions and being more assertive than those with
the active gene. The dominance over others in your social group can be risky behavior, and
this gene appears to keep that behavior in check. The significances of this study was that it
has shown that the same gene can have two very different functions depending on which
parent each copy is inherited from. It seems that the mother and father are using different
strategies to help their offspring, one focused on the body and the other on the mind.
SLIDE 18 The infidelity gene (the adventure): the dopamine D4 receptor (DRD4)
variant 7 (DRD4-R7) The D4 receptor gene contains a 48 bp Variable Number Tandem
Repeat (VNTR, encoding 16 amino acids) polymorphism in the third exon, which results in
considerable heterogeneity (2-11 repeats). The 48-bp repeat is thought to reside in the third
cytoplasmic loop of the receptor protein and this variation has been shown to affect the
function of the D4 receptor in vivo. The most common alleles consist of four repeats (4R)
and seven repeats (7R). It was suggested that there may also be variation in G-protein
interactions among the different forms of the receptors. The genetic link of promiscuous
behavior was established by a research team after gathering the intricate history of sexual
behavior and relationships of 181 young adults as well as their DNA collected from cheek
swabs. The samples were screened for the promiscuity-inducing DRD4 gene variant. The
genetic findings were correlated with the personal data of the subjects and the numbers show
that those with the “sexual” DRD4 were twice more likely to have a history of one-night
stands (50% reported promiscuous encounters) than those who did not have the gene (only
20% reported promiscuous encounters). DRD4 is a dopamine receptor gene which is
responsible for a certain neurological process that includes motivation, pleasure, cognition,
and motor control. DRD4 encodes dopamine receptor D4 on chromosome 11. DRD4 helps to
moderate certain behaviors such as promiscuity and infidelity. However, the relationships are
associative and that not all individuals with the sexual DRD4 gene will be disloyal to their
partners. It just shows they have the tendency toward both infidelity and uncommitted onenight stands. DRD4 is the "thrill-seeking" gene, which means that it's also the "loving horror
movies" gene, and, less charmingly, the "gambling addiction" gene.
SLIDE 19 The liberalism gene: DRD4-R7 Scientists determined that people who carry a
variant of the DRD4 gene are more likely to be liberals as adults, depending on the number of
friendships they had during high school. The 7R variant of DRD4, a dopamine receptor gene,
had previously been associated with novelty seeking. The researchers theorized novelty
seeking would be related to openness, a psychological trait that has been associated with
political liberalism. However, social environment was critical. The more friends gene carriers
have in high school, the more likely they are to be liberals as adults. Having many friends can
move a person with two copies of 7R allele almost halfway from being a conservative to
moderate or from being moderate to liberal. The sample consisted of over 2,574 individuals.
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Respondents were asked during their high school years to name five female and five male
friends.
SLIDE 20 Impulsivity is a broad term describing behavior characterized by action without foresight,
decreased inhibitory control and a lack of consideration of consequences. Although impulsivity can be an
adaptive dimension of personality, intolerance for delay, disinhibition and the inappropriate weighting of
contingencies are maladaptive. The behavioral manifestations of impulsivity include suicide, addictions,
attention deficit hyperactivity disorder and violent criminality, as well as antisocial personality disorder. To
detect novel alleles that influence impulsivity, severely impulsive Finnish criminal offenders and matched
controls were studied. HTR2B Q20* is associated and co-segregates with disorders characterized by impulsivity,
reflected in severe crimes committed on the spur of the moment—as documented by criminal and clinical
records—and under alcohol intoxication, a condition where impulse control is impaired. Thus, the Q20* allele
can be regarded as one determinant of behavioral variation. However, the presence of Q20* was not in itself
sufficient: male sex, testosterone level, the decision to drink alcohol, and probably other factors such as stress
exposure, all have important roles. Htr2b-/- knockout mice exhibit increased impulsivity and novelty seeking.
SLIDE 21 Genetics of behavior – the problem No single gene determines a particular behavior. Behaviors
are complex traits involving multiple genes that are affected by a variety of other factors. This fact often gets
overlooked in media reports hyping scientific breakthroughs on gene function, and, unfortunately, this can be
very misleading to the public.
SLIDE 22 Competition and cooperation What could be the reason that soccer, the favorite sport of the world
cannot spread in America? It is a general belief that the American society there is a very strong competition
among individuals. However, it is only one half of the story. There is a strong cooperation within groups, such as
in a football team. In American football the goal pass is as important as the goal itself, which encourages
cooperation.
SLIDE 23 Misunderstood Darwinism Social Darwinism was a belief, popular in the late Victorian era in
England, America, and elsewhere, which states that the strongest or fittest should survive and flourish in society,
while the weak and unfit should be allowed to die. Herbert Spencer, the father of Social Darwinism as an ethical
theory, was thinking in terms of elitist, "might make right" sorts of views long before Darwin published his
theory. However, Spencer quickly adapted Darwinian ideas to his own ethical theories. The concept of
adaptation allowed him to claim that the rich and powerful were better adapted to the social and economic
climate of the time, and the concept of natural selection allowed him to argue that it was natural, normal, and
proper for the strong to thrive at the expense of the weak. After all, he claimed, that is exactly what goes on in
nature every day. However, Spencer did not just present his theories as placing humans on a parallel with nature.
Not only was survival of the fittest natural, but it was also morally correct. Indeed, some extreme Social
Darwinists argued that it was morally incorrect to assist those weaker than oneself, since that would be
promoting the survival and possible reproduction of someone who was fundamentally unfit. Further, social
Darwinism considers the struggle among nations as an aim to be followed. Colonialism was seen as natural and
inevitable, and given justification through Social Darwinian ethics - people saw natives as being weaker and
more unfit to survive, and therefore felt justified in seizing land and resources. Social Darwinism applied to
military action as well; the argument went that the strongest military would win, and would therefore be the
fittest. Casualties on the losing side, of course, were written off as the natural result of their unfit status. Finally,
it gave the ethical nod to brutal colonial governments who used oppressive tactics against their subjects. In its
most extreme forms, Social Darwinism has been used to justify eugenics programs aimed at weeding
"undesirable" genes from the population; such programs were sometimes accompanied by sterilization laws
directed against "unfit" individuals. The American eugenics movement was relatively popular between about
1910-1930, during which 24 states passed sterilization laws and Congress passed a law restricting immigration
from certain areas deemed to be unfit. Social Darwinist ideas, though in different forms, were also applied by the
Nazi party in Germany to justify their eugenics programs. Another of these social interpretations of Darwin's
biological views, later known as eugenics, was put forth by Darwin's cousin, Francis Galton, in 1865 and 1869.
Galton argued that just as physical traits were clearly inherited among generations of people, so could be said for
mental qualities (genius and talent). Galton argued that social morals needed to change so that heredity was a
conscious decision, in order to avoid over-breeding by "less fit" members of society and the under-breeding of
the "more fit" ones. Galton claimed that the less intelligent were more fertile than the more intelligent of his
time. Galton did not propose any selection methods; rather, he hoped a solution would be found if social mores
changed in a way that encouraged people to see the importance of breeding. He believed he could know the
content of a man’s character from the bumps on his skull.
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