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What are the factors that contribute to genetically identical individuals behaving differently?

What are the factors that contribute to genetically identical individuals behaving differently?


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If you run the same task on a pair of identical computers, you will end up getting the same results, even with the same response time.

But let's say you line two different person, and ask them the exact same question. Each will answer totally different, even if they are twins, raised in the same family, went to the same school and shared the same roof, and probably had the same experience in life. One of them may love carrots, one may not.

The question is, what is generating such different behaviour and way of thinking? Aren't they sharing the same genes?

If yes, the question is still standing.

If no, then we'll have another question:

If we create 2 identical clones of a person, raise them in the same situation, will they think identical too? If not, why? And what's the reason of this?


Your question has actually more to do with developmental biology and the origin of phenotypic variance in populations than with neuroscience.

Here is a list of factors which variance explain observed phenotypic variance in a population:

  • Genetics (incl. additive, dominance and epistatic variances)
  • Environment (incl. macro and micro environments)
  • Developmental noise (incl. cellular noise)
  • Epigenetic
  • All the covariances among above factors

Of course, when you consider a pair of monozygotic twin as your population, there is little to no genetic variance. They will also likely experience little epigenetic variance. Assuming they live together, practice the same sport, eat the same type of food, etc… then they will also experience little macro-environmental variance. Micro-envrionmental variance and developmental noise are probably the main factors causing these two hypothetical twins to differ.

You might want to read the post Why is a heritability coefficient not an index of how “genetic” something is? to better understand the current post.


The Role of Genetics in Alcoholism

Daniel B. Block, MD, is an award-winning, board-certified psychiatrist who operates a private practice in Pennsylvania.

Dylan M Howell Photography / Getty Images

Alcoholism seems to run in some families. Is there any scientific evidence that your genes may predispose you to become an alcoholic if your parents or grandparents are? While many studies have been done and experts agree that there is a hereditary connection, genetics is not the only factor and we don't quite know the full impact it has on alcoholism.


Major Depression and Genetics

How common is major depression? At least 10% of people in the U.S. will experience major depressive disorder at some point in their lives. Two times as many women as men experience major depression.

How do we know that genes play a role in causing depression? Scientists look at patterns of illness in families to estimate their “heritability,” or roughly what percentage of their cause is due to genes. To do this we find people with the disease who have a twin, and then find out whether the twin is also ill. Identical (monozygotic) twins share 100% of their genes, while non-identical (“fraternal” or dizygotic) twins share 50% of their genes. If genes are part of the cause, we expect a patient’s identical twin to have a much higher risk of disease than a patient’s non-identical twin. That is the case for major depression. Heritability is probably 40-50%, and might be higher for severe depression.

This could mean that in most cases of depression, around 50% of the cause is genetic, and around 50% is unrelated to genes (psychological or physical factors). Or it could mean that in some cases, the tendency to become depressed is almost completely genetic, and in other cases it is not really genetic at all. We don’t know the answer yet.

We can also look at adoption studies, to see whether an adopted person’s risk of depression is greater if a biological parent had depression. This also seems to be the case.

What about non-genetic factors? There are probably many non-genetic factors that increase risk of depression, many of which are probably not yet known. Severe childhood physical or sexual abuse, childhood emotional and physical neglect, and severe life stress are probably all risk factors. Losing a parent early in life probably also increases risk to some extent.

If someone has a family history of depression, are they at very high risk? If someone has a parent or sibling with major depression, that person probably has a 2 or 3 times greater risk of developing depression compared with the average person (or around 20-30% instead of 10%).

The situation is a little different if the parent or sibling has had depression more than once (“recurrent depression”), and if the depression started relatively early in life (childhood, teens or twenties). This form of depression is less common – the exact percentage of the population is not known, but is probably around 3-5%. But the siblings and children of people with this form of depression probably develop it at a rate that is 4 or 5 times greater than the average person.

Is there a “depression gene”? Some diseases are caused by a single defective gene. Cystic fibrosis, several kinds of muscular dystrophy, and Huntington’s disease are examples. These are usually rare diseases. But many common disorders like depression, diabetes and high blood pressure are also influenced by genes. In these disorders, there seem to be combinations of genetic changes that predispose some people to become ill. We don’t yet know how many genes are involved in depression, but it is very doubtful that any one gene causes depression in any large number of people.

So no one simply “inherits” depression from their mother or father. Each person inherits a unique combination of genes from their mother and father, and certain combinations can predispose to a particular illness.

How are major depression and bipolar disorder related? Most people who suffer from depression do not have episodes of mania. We use the term major depression for depression without mania. Most people who experience mania also have major depression. We use the term bipolar disorder (or manic-depression) for this pattern. Major depressive disorder and bipolar disorder are the two “major mood disorders.” For more information on the symptoms of mania abd bipolar disorder, see the links at the bottom of this page. Most people with major depression do not have close relatives with bipolar disorder, but the relatives of people with bipolar disorder are at increased risk of both major depression and bipolar disorder.

What about major depression and anxiety disorders? There are probably genetic changes that can increase the predisposition to both major depression and to certain anxiety disorders including generalized anxiety disorder, panic disorder and social phobia. Also, some people have a more general lifelong tendency to experience unpleasant emotions and anxiety in response to stress. Psychologists use terms like “neuroticism” and “negative affectivity” to refer to this tendency, and people who have it are also more likely to experience major depression.

However, many people who develop major depression did not have this type of personality before their depression started.


Environmental Differences

While identical twins form with the same set of genes, human development is not just genetic. The environment also has an impact. So, beginning in the early environment of the womb, external influences can change the appearance of twins. For example, some monozygotic twins share a placenta. One twin may have a more advantageous connection to the placenta, receiving the first run of nutrients.

This situation can cause a size discrepancy between the babies, a physical difference that continues as they grow up. Twin-to-Twin Transfusion Syndrome (TTTS) is another condition that affects twins in the womb and can impact their development.

While most twins grow up in the same home environment, there are many circumstances that create differences in the children's appearances, personalities, and interests. As the twins approach the teen years, they may even seek to establish dissimilar qualities in order to establish individual identities.


Introduction to LS3.B

Variation among individuals of the same species can be explained by both genetic and environmental factors. Individuals within a species have similar but not identical genes. In sexual reproduction, variations in traits between parent and offspring arise from the particular set of chromosomes (and their respective multiple genes) inherited, with each parent contributing half of each chromosome pair. More rarely, such variations result from mutations, which are changes in the information that genes carry. Although genes control the general traits of any given organism, other parts of the DNA and external environmental factors can modify an individual’s specific development, appearance, behavior, and likelihood of producing offspring. The set of variations of genes present, together with the interactions of genes with their environment, determines the distribution of variation of traits in a population.


16 factors that influences people’s intelligence

Ale notices a wide variety of individual differences in people’s intellectual abilities. Some are more intelligent than others. The differences are so much that some change the course of human civilization through their intellectual innovations, a few others even find it difficult to master a problem simple addition.

The individual differences that exist among all of us are the products of two general and broad factors: hereditary environmental.

Hereditary factors are based on the genetic make up of the individual influences growth and development throughout life. The offspring inherits genetic characteristics from his parents. The environmental factors cc of the influence of parents, family, friends, schooling, society, culture, and all other experiences to which the child is exposed right from the moment of conception.

The nature-nurture controversy has philosophical roots. In the 1600s, Locke, English philosopher, argued that the mind of a newborn is a blank: a tabula rasa on which the environment writes his life history. Locke believed that environment acts as the sole determinant of development. On the con the French philosopher, J. J. Rousseau suggested in the 1700s that people’s natural characteristics (i.e., genetic factors) mostly influence developmental process subject to the corrupting influences of the environment.

The nature-nurture question has been vehemently debated for decades. At present, psychologists agree that both nature and nurture interact to pro specific developmental patterns and competence. The question has changed from which (heredity or environment) influences behavior to how and to what extent heredity and environment shape the developmental proc No body is born without a genetic make up, or no one grows up free environmental influences.

Both heredity and environment are important, it is unwise to determine their relative influence. Even then, the de concerning their relative influence remains still active with different thee emphasizing either the role of heredity or the role of environment (Scarr, 1996). These factors are discussed below in detail.

1. Hereditary Factors

Heredity refers to genetically transmitted characteristics from generation to the next. We inherit genetic code from parents. Because of genetic code, a fertilized human egg never grows into a dog or a mouse or any other animal. Person’s genetic heritage is called genotype. The genotype expresses itself in observable appearance and behavior, which is called phenotype. The phenotype includes height, weight, eye color, and psychological characteristics such as intelligence, personality and creativity.

The genetic code provides the base on which phenotype grows and manifests. How can we know that human intelligence has a genetic basis? To do so, we have to infer the underlying genotypes from the observable phenotypic behavior.

A strategy to understand genotypes from phenotypes is to examine the similarities between the intelligence level of children, and their parents and relatives. Francis Galton (1885) was of the view that intelligence is largely inherited, and it runs in families. Researchers have found “that parents with high IQs tend to have children with high IQs, and parents with low IQs have children with relatively low IQs (Crooks and Stein, 1995).

Correlations between IQs of brothers, sisters, children and their parents, and their distant relatives indicate that intelligence has a strong hereditary component (Kagan and havemann, 1976). The correlation between the IQs of one child and another person selected at random would tend to be zero, while among the related individuals the correlations would be relatively high.

Correlation coefficient provides a measure of the strength of relationship between two variables, and bound by limits from -1.00 to +1.00. The higher is the correlation coefficient le higher is the strength of relationship.

In more recent times, Arthur Jensen (1969) raised a hostile controversy ‘hen he argued that intelligence is primarily inherited. He examined several studies on intelligence, many of which involved comparisons of identical and fraternal twins. Jensen found support in these studies for his argument in favor of the genetic influence on intelligence.

He claimed that clear-cut genetic differences are present in the average intelligence of races, nationalities, and social classes. He stated that blacks have lower genetic intelligence than whites, and that is why they do not perform as well as whites on intelligence tests.

He rid others have placed the importance of heredity’s influence on intelligence at about 80 percent, leaving only 20 percent to be manipulated by the environment, He believed that environmental manipulations can at best reduce group differences in intelligence, but cannot abolish it altogether. But Jensen’s views have been severely criticized, and he has been labeled as a racist.

Psychologists have drawn evidence from a number of studies to examine the relative influence of hereditary and environmental factors on intelligence The two kinds of studies discussed below are: (a) studies of twin children and (b) studies involving adopted children.

2. Twin studies:

Twins are of two types: identical twins and fraternal twins Identical twins originate from a single fertilized egg and share the same gencode. The fraternal twins arise from two different eggs fertilized by two different sperm cells. While identical twins show a 100 percent genetic overlap, fraternal twins have 50 percent genetic similarity, which is no greater than that between ordinary siblings. If identical twins turn out to be more simile their intelligence as compared to fraternal twins, the evidence for the hereditary factors would be strong.

The average correlation coefficients between the IQs of children having different degrees of genetic similarity insightful analysis of the correlations will clarify several points regarding the relative role of heredity and environment in shaping individual’s intelligence.

3. Relationship Median Correlation

Identical twins reared together – .86

Identical twins reared apart – .72

Fraternal twins reared together – .60

Siblings reared together – .47

Siblings reared apart – .24

Parent and child living together – .42

Parent and child separated by adoption – .31

Genetically unrelated children reared together – .25

Genetically unrelated foster parents and foster child – .15

The correlation between the IQs of identical twins reared together is which is substantially higher than the correlation of fraternal twins reared together (.60). Furthermore, identical twins reared apart in different environments show a high degree of similarity (.72) in their intelligence as compared to the fraternal twins reared together (.60).

The finding that identical twins raised in different environments are similar in their intellectual abilities than fraternal twins reared in the same environment suggests a strong genetic influence on intelligence. However, the role of the environment cannot be ruled out, because the correlation drops from .86 to .72 as the environment changes for the identical twins.

4. Adoption studies:

Another line of evidence comes from the studies on adopted children. In one study (Horn, 1983), the correlation between the IQs of children and their biological mothers (whom they had never seen) was .28, which was much higher than a correlation of .15 between their IQs and their adoptive mothers.

Other studies have also shown that children’s intelligence is more similar to their biological parents than to their adoptive parents (Scarr and Carter-Saltzman, 1983). This pattern of similarity persists into adolescence. Those favoring an environmental position argue that children of poor and under-educated parents, when adopted into family of high socio­economic status, exhibit very large increase in their IQ scores.

But the findings showed that when the socioeconomic status of both biological and adoptive parents is equal, the IQs of adopted children do not rise instead, it is found to be more similar to their biological parents. All these findings lend support to hereditary influence on intelligence.

5. Environmental Factors

Heredity alone cannot account for all the individual differences in intelligence. Environment also has a role to play. Environment consists of a wide range of stimulations that the child is subjected to. He lives and grows in his environment. It provides him the necessary input and experiential base for intellectual development. Enrichment or deficiency of the environment would obviously produce differences in his abilities.

The information given above can be used to support environment’s role. Though fraternal twins and siblings share the same genetic similarity (the genetic overlap in both cases is 50 percent), the correlation between the IQs of fraternal twins is a bit higher than that for ordinary siblings (.60 versus .47).

This is because environmental opportunities and experiences are more similar for fraternal twins than for ordinary siblings. When researchers have manipulated child’s environment by providing extra intellectual input, they have observed a remarkable improvement (up to 30 IQ points) in the IQ scores of children.

Hence, the role of environment cannot be underestimated. Furthermore, we can change the environment the child, not his genetic make up. Thus, irrespective of genetic make adults should carefully monitor child’s environment to help him perform at optimal efficiency level.

Environment starts showing its actions right from the moment of chi conception. Both the prenatal environment (when the baby/fetus is in mother’s womb), and the postnatal environment (after the child is born) influence intellectual capabilities of the child.

6. Prenatal Environment

The prenatal stage is extremely important as a fertilized egg is shaped the form of a human being during this period. Rapid development takes place in major organs and brain cells. If things go wrong during this period, the effects are nearly irreversible or are very difficult to correct. The major prenatal environmental influences are: (a) mother’s nutrition, (b) mother’s emotional state, (c) illness of the mother, (d) mother’s use of drugs, and (e) birth complications.

An undernourished mother cannot provide adequate nutrition to the grow baby. As a result, the baby is likely to be underweight, and more susceptible to diseases. Lack of nutrition would have an adverse impact on the mental development of the child. Mothers who are anxious and tense are also likely deliver infants who would be irritable and show problems in sleeping and eating

Maternal diseases like rubella, syphilis, AIDS, diabetes, and high blood pressure may produce permanent adverse effects on the baby. The brain d of the baby would either be damaged or not grow properly. The intellect development may be arrested. The consequences may be devastating to such an extent that later environmental enrichment programs for the child may totally ineffective.

Drugs taken by mothers can have tragic effects on the unborn child. Alcohol and nicotine are very dangerous for pregnant mothers. The unborn baby may develop fetal alcohol syndrome, which is a condition of retarded physical and mental growth. The children of such mothers may show permanent physical and mental impairment.

If the baby suffers from birth complications such as lack of oxygen at the time of birth, he may suffer permanent brain damage. He would be born, as a mentally retarded child about whom very little can be done. Due attention to ensuring a healthy prenatal environment is necessary for any child to have a fuller development of his intellectual capabilities.

7. Postnatal Environment

When we speak of environmental determinants of intelligence, we ordinarily mean the environment the child faces after he is born. Environment consists of a heterogeneous array of stimulations ranging from home experiences to the ecology of the natural habitat. Enriched environment accelerates cognitive development, while impoverished environment produces just the opposite effect.

8. Home environment

Home is the first learning institution for the child during his early years of development. Needless to mention that it exercises tremendous influence on child’s understanding of the external world, and his conceptions of success and failure. The home provides an identity for the child, builds his self-concept, and prepares him to face the world.

The home environment consists of all the mental and behavioral transactions taking place among the family members. The environment can be stressful or supportive for the child. A supportive and warm home environment that encourages exploration, curiosity, and self-reliance leads to higher intellectual competence in children (Kelly & Woreil, 1977).

In unsupportive home environments, where the families members punish or reject the child, or parents are extremely authoritarian and impose a set of rigid rules and regulations on the child, child’s intellectual competence becomes low. A restrictive home atmosphere inhibits early exploration and curiosity in children, and creates high anxiety in the child as a result of which his natural potentials fail to grow to the optimal level.

The home environment also influences child’s emotions, motivations and beliefs, which are closely linked with intellectual competence.

9. Parent-Child interaction

Parents are the first teachers for the child. The nature of mental behavioral transactions between the parents and the child has a critical influence on his intellectual competence. Children’s intellectual develops is faster when parents provide emotional security, make the family environment more supportive, praise the child’s achievement, allow independence, support the intellectual achievement of children. On the contrary, with stressful family conditions and protective parents encouraging dependence in child the child’s intellectual development suffers.

Both cultural and sex differences in intellectual abilities result from pare values and expectations for children’s achievement. A study by Ha Stevenson revealed that Chinese and Japanese children in the United States show exceptional ability in mathematics, because their parents emphasize achievement orientation in children during their early formative period development.

Parental expectations for boys and girls differ and are reflected in their achievements. Parents consider mathematics more important for boys than girls. There are many studies to suggest that girls outshine boy language skills, whereas boys show superior performance in mathematical and spatial tests.

The mother is more important than the father in determining the intellectual level of the home environment, because she spends more time with child When the mother is the better-educated parent, the intellectual compete of the college going and university students is higher than those having father as the better-educated parent.

In a study (Kagan & Moss, 1962), it was sir that high achievement in boys was associated with high maternal reinforcement and encouragement during the first three years of life. It should, however kept in mind that although parent-child interaction is an important determinant of achievement in children, other factors such as social class, education social opportunities set important limits on children’s attainment.

10. Social and environmental deprivation

If the environmental opportunities and stimulations are low, children show poor cognitive performance. The most frequently noted study was the one conducted by Skeels (1966) involving 25 children reared up in orphanages with very little stimulation. At about 18 months of age, 13 of these children were transferred to another setting, where older retarded women took care of them. After about 2 years, these children gained 28 IQ points. The other 12 children, who stayed back in the unstimulating orphanage, exhibited a 26- point drop in their IQs.

The two groups of children also showed different patterns of adjustment and personality characteristics as adults. A follow-up study after 20 years revealed that the 13 children removed from the orphanage had normal intellectual functioning and social adjustment. The intellectual condition of those 12 children who were in the orphanages was very poor.

Studies show that longer the children remain in impoverished environment, the more depressed their IQs would be (Asher, 1935). For example, with the introduction of schools, roads and radios in a community in the USA in 1930s, the average IQ of individuals increased by 10 points (Wheeler, 1942).

In another study J. Hunt (1982) investigated the effects of enrichment on 11 children in Iranian orphanage, who were developmentally and emotionally retarded. They were rescued, and put into special enriched environmental program by Hunt who arranged specially trained caretakers for them.

They provided these infants special attention, played verbal games with them, and responded to their difficulties, problems, and wants. The effect was striking in that all displayed large improvement in their language skill, and social interactions with people and events, and began behaving intelligently. The Project Head Start in the year 1965 in USA provided compensatory education on social skill, and special intellectual training. The program was initially effective in raising the IQs of children coming from the disadvantaged homes in slum areas.

Studies conducted by Dash and Das (1984, 1989) reveal that an opportunity for education such as schooling significantly influences children’s cognitive capacities.

In a study in rural India, they have shown that schooled children show superior performance on a variety of intellectual tasks compared to their unschooled age-mates. Schooling improves children’s abilities to memorize, reason, and classify using a variety of principles.

Many of the intellectual processes either develop slowly or do not develop at all in children, who do not attend schools. School provides an enriched social environment for children, and allows their thought processes to grow free from the concrete physical and social contexts. Similar findings have been obtained in African countries by Scribner and Cole (1979).

Are the adverse effects of impoverished environments reversible? Can children suffering the ill effects of social deprivation increase their IQs, when raised later in stimulating environmental conditions? Some argue that the adverse effects operate on a relatively permanent basis. But other researchers have shown that early intellectual retardation can be overcome by providing adequate enriched environmental experiences (Kagan, 1972).

11. Socioeconomic status (SES)

Children of the upper socioeconomic strata of the society are exposed to more intellectual stimulation, get better social opportunities, and are nurtured with better nutrition. All these are believed to influence their intellectual development in a positive direction. The index of socioeconomic status (SES) is based on parental education, occupation, and income. The higher is the socioeconomic status of the parents, the higher is the average IQ of children.

The children of low socioeconomic status score approximately 10 to 15 IQ points below the middle-class and higher-class children (Hall and Kaye, 1980). These differences are present by the first grade and are sustained throughout the school years. Parental occupation is closely related to the IQ level of children (Harrell and Harrell, 1945).

The intellective support provided to children at home differs from one SES to another. Moreover, children from varying SES levels bring different attitudes and cognitive styles to the problem-solving situation, which affect their performance (Yando, Seitz and Zigler, 1979).

In Orissa, Jachuck and Mohanty (1974) found that children of high SES performed significantly better than children from low SES on a variety of intellectual tasks. Even older children from low SES performed poorly than the younger children of high SES. For low SES children, they observed progressive retardation in intellectual skills. Rath, Dash and Dash (1975 reported the adverse effects of social class on intellectual reasoning. These finding have been supported by a number of studies conducted in the Indian subcontinent.

12. Race and culture

Many studies have noted racial and cultural differences in performance on lard intelligence tests (Jensen, 1969 Kennedy, 1966). Jensen (1969) observed clear differences in the cognitive competence of whites and blacks,studies conducted by Lesser, Fifer, and Clark (1965) investigated the verbal reasoning, number facility, and space conceptualization of children from : groups: Jewish, Chinese, Puerto Rican and black.

They found that racial membership significantly influenced both the pattern and level of intellectual sentence. In fact, racial differences were more prominent than the SES differences. Culture refers to a system of beliefs, attitudes, and values that assed from one generation to the next. In Indian context, there are prominent subcultures defined by caste groups, and traditional parental occupations.

The socialization practices in these subcultures are different. Studies have been conducted in rural Orissa comparing children of different groups.

The Harijan children scored west among the three groups and the Brahmins scored the highest. The Brahmins have a highly verbal articulate culture compared to the other groups studies conducted in this region (Das and Singha, 1974 Jachuck and Mohanty, 1974) have reported significant differences in the cognitive level of children differing by caste, culture, and SES.

It may be unfair to compare the performance level of children from different cultures, as the skills required for successful adaptation in different cultures great deal The skills tapped by the standard cognitive tests are those that are demanded in more technologically advanced cultures and higher SES groups.

As a result the tests are biased in favor of their competence, and it is no wonder that we find inferior performance of lower caste children on these. The appropriateness of the test items has to be considered in any investigation comparing the performance of children from various cultural and groups.

13. Sex differences

The overall IQ scores of boys and girls are very similar. There is some evidence that sex differences exist for particular kinds of cognitive abilities Review of a number of studies has shown that females are superior in language skills, verbal fluency, and reading, while males are superior in mathematical reasoning and spatial abilities (Oetzel, 1966). While neither sex is sup the two sexes show different patterns of intellectual abilities.

These have been supported by several researchers. Some argue that intellectual differences between sexes reflect different child-rearing practice socio-cultural training. The parents and the society train boys and differently in terms of what to expect from them. It is known that intelligence related to personality characteristics.

Boys are socialized in a way so promote self-reliance and competence, which are positively correlate intelligence. On the other hand, the traits are discouraged in girls so mi that high intelligence is often considered a masculine quality.

The sex differences also partly result from the fact that many items standardized intelligence tests are biased in favor of the male population. Hence sex differences are the products of the test itself. Researchers differ in their convictions regarding sex differences. A group of researchers that sex differences are reflections of constitutional and genetic difference between males and females. The most reasonable conclusion is that differential abilities are the products of some combination of genetic and environmental factors.

15. Personality dispositions

There is some evidence to suggest that changes in IQ are related to general pattern of adjustment and personality. In a longitudinal study (5 Baker, and Nelson, 1958), 140 children were tested at intervals bet and 12 years of age. The 35 children, whose IQs increased remarkable found to have personality traits of assertiveness, independence, self-in and competitiveness.

On the contrary the 35 children who showed a d trend were found to lack these traits. If the personality traits were not acceptable, the advantages would be minimized. For example, child show temper tantrums have been found to display drops in their IQs (Peskin, 1964). Good intellectual functioning requires the ability to harness one’s emotions and utilize them in a constructive manner.

16. Physiological conditions

The physiological conditions such as nutrition, health, drugs, disease, and physical injury affect the cognitive competence of the child. Healthy body gives a healthy mind. The mental development is associated with biochemical processes and hormones within the body. The biological processes within the body provide a necessary but not sufficient condition for intellectual development.

Poor health and susceptibility to diseases would retard the growth of brain cells, and consequently the intellectual skills. Physical injury to the brain during early childhood years is likely to result in minimal brain damage thus seriously restricting the development of intellectual faculty. Similarly, intoxicating drugs and alcohol consumption would adversely affect the biological processes and the development of brain cells.

Thus, the internal physiological conditions are critical for the expression of intelligent behavior.


Personality Essential Reads

Wandering Into Wonder

Does Personality Predict Who Will Cheat in a Relationship?

Lindberger concludes, "Our findings show that development itself contributes to differences in adult behavior. This is what many have assumed, but now there is direct neurobiological evidence in support of this claim. Our results suggest that experience influences the aging of the human mind. When viewed from educational and psychological perspectives, the results of our experiment suggest that an enriched environment fosters the development of individuality.”

The combination of neurogenesis and neuroplasticity brings together “old” neurons with "new" neurons to shape an adaptable personality. Scientists are beginning to believe that "new" neurons, work with specialized glial cells in the adult brain to mediate certain types of plasticity, and the malfunction of such processes may cause neurological or psychiatric disease. These findings could lead to new medical treatments.

It is exciting to have scientific confirmation that there is a link between cognitive challenges, adult brain neurogenesis, and the development of individuality. Each of us has the ability to reshape our brains and influence our individuality by simple cognitive and behavioral choices we make each day. Mindset is not fixed and individuality is not hardwired. Neurogenesis and neuroplasticity offers each of us a fresh start everyday.


What Makes People Happy? Genetics vs. Circumstances

Happiness and Your Genetic Makeup

Research shows that people’s genetic makeup is responsible for about 50 percent of their happiness.

Genes play a very important role in people’s personalities, including how they tend to respond to what happens to them. Our genes determine the structure and activity of our brains. Some lucky people’s brains are structured in ways that promote positive emotions, and some of us have brains that respond more easily to negative emotions.

This is a transcript from the video series Understanding the Mysteries of Human Behavior. Watch it now, on Wondrium.

Many studies have conclusively shown that about 50% of the variability that we see in the degree to which people experience positive and negative emotions is due to genetic factors.

For example, research shows that identical twins are more similar in their level of happiness—or unhappiness—than regular brothers and sisters. That’s true even if the twins have been separated at birth and raised by different families. Their identical genes create identical brains that make them similar in how happy—or unhappy—they are.

…identical twins are more similar in their level of happiness—or unhappiness—than regular brothers and sisters.

They won’t be identical in happiness, of course, because genetic influences account for only 50% of happiness. But identical twins are certainly more similar emotionally than other siblings.

You can see inborn differences in happiness in very young infants, long before their circumstances have affected them very much. Some babies are naturally more bubbly and happy, and other babies are more unhappy and fussy.

A Baseline of Happiness

The best way to think about these genetic influences is to think of yourself as having some typical baseline of happiness. Good events will temporarily increase your happiness, and bad events will make you unhappy. But after those events have passed and nothing particularly good or bad is going on in your life, how happy are you? You will return again and again to your typical baseline, almost as if it’s some kind of a set point.

In all likelihood, you can’t change this baseline or resting level of happiness. But that doesn’t mean that those of us whose brains lead us more toward unhappiness can’t be happy we just have to work harder at it.

How Our Behavior Factors In

But even after we account for the 50% of happiness that’s due to genetic factors and 10% due to our life circumstances, there’s still 40% remaining. That 40% is due to our behavior—what we do, how we think, and our intentional activities. People who are happier do things differently than people who are less happy.

The good news is that research suggests that if we all do things the way that happy people do, we’ll be happier too. There are many different ways to be unhappy, but happy people are alike in many ways.

…research suggests that if we all do things the way that happy people do, we’ll be happier too.

Happy people differ from unhappy people both in what they do and how they do what they do. For example, in general, research shows that happy people spend more time with their friends and family than unhappy people do, and happy people also nurture and enjoy those relationships more.

Research shows that happy people spend more time with their friends and family than unhappy people do. (Image: By Liderina/Shutterstock)

There’s something about having social connections and close relationships that usually promotes happiness. But, that doesn’t necessarily mean that simply forcing yourself to spend more time with your family is necessarily going to make you happy, unless you approach it in the right way.

Subjective Well-Being

To understand this point, consider a different word than happiness for the positive emotional state we all seek. Happiness doesn’t quite capture what most of us probably want. When people imagine a happy person, they often think of someone smiling or laughing who is experiencing a surge of pleasure because something good has happened to them.

But, what most people want more than occasional episodes of happiness is an overriding sense of contentment and pleasure—a sense of well-being that goes a little bit deeper than happiness per se. Of course, people want moments of happiness, and that’s fine, but no one can sustain happy feelings all the time. But people can have a long-lasting sense of contentment, satisfaction with themselves and with life, peace of mind, and general positive feelings.

Let’s call this sort of positive emotion subjective well-being to distinguish it from momentary happiness that’s caused by something happening in particular, such as getting a raise or winning an award.

People who generally live with a sense of high subjective well-being differ from people who report lower subjective well-being in the degree to which their lives are characterized by eudaimonia. Most people may not be familiar with the concept of eudaimonia, but it is very useful in understanding happiness and subjective well-being. Eudaimonia can be defined as living one’s life in a way that focuses on things that are intrinsically important for human well-being.

Eudaimonia can be defined as living one’s life in a way that focuses on things that are intrinsically important for human well-being.

Intrinsic Importance

If you were asked to make a list of all of your goals—things that you wanted to get in the next year or two—you might list many different things. You might want to get a raise, to lose weight, to achieve some goal at work, to spend more time with your children or your friends, to get a bigger house, to retire, or whatever. All of these goals are fine, but some of them are more intrinsically important to your well-being.

By intrinsically important, some of these goals are pursued for their own sake rather than to get something else. Spending more time with your children or friends is probably an intrinsic goal. If you want to spend more time with somebody, it’s probably because you want to spend more time with them, not so that you can obtain some other goal.

By intrinsically important, some of these goals are pursued for their own sake rather than to get something else.

On the other hand, making money is not an intrinsic goal. You don’t want to make money just to have piles of money you want money because it will allow you to obtain or to do other things. Money isn’t intrinsically rewarding in the same way that you may find it intrinsically rewarding to spend time with people you love, to play golf, or to paint.

Henry David Thoreau once wrote that “Most men lead lives of quiet desperation.” Life situations and bad experiences contribute to their desperation and unhappiness, of course, but not nearly as much as most people assume.

We need to understand that our day-to-day happiness and subjective well-being depend far more—at least four times as much—on how we approach life than on what life brings our way. It’s this understanding that may open the door to greater happiness and life satisfaction for all of us.

Common Questions About What Makes People Happy

According to Ed Diener , PsyD, there are five factors to what makes people happy : positive thinking first and foremost, useful and pleasant social relationships, a relaxed temperament and predisposition for adaptation, income level, and the society and culture you live in.

What makes people happy is subjective but can be defined as a sense of satisfaction, purpose, and contentment when life fulfills the majority of your most pressing needs and wants.

Of the many theories, most agree that happiness is somewhat of a survival mechanism. Happiness makes people more attractive and interesting which helps attract others who can offer their skills for survival and thriving .

According to studies, intelligence can bring happiness. Low levels of happiness tend to correlate positively with low income, stress, and poor physical or mental health which all correlate with lower intelligence based on IQ.


Effect on Different Aspects of Human Development

Nature can be thought of as the factor that defines certain physical characteristics as well as something that creates an outline for the innate abilities and potentials that we possess. Nurture on the other hand is the factor that takes these genetic predispositions and shapes it so that these abilities can be realized (meaning they can be achieved). From this we can infer that both play a role in shaping us as an individual. What we will now look at is how the two of them interact together in our developmental process.

Behavior, Personality, and Intelligence
As we know already, our genetic makeup bestows on us our physical characteristics. Along with it, certain underlying traits are also heritable. For example behavioral traits like what language we speak, how we interact with people, how we respond to certain situations, are all molded by ‘nurture’ – this is obvious because the environment in which we are brought up in, shapes these factors over time. But it is also noted that some of these traits are partially heritable. For example, certain disorders are genetically inherited. But their manifestation might only become more apparent if that disorder is somehow cultivated. Aggressive behavior is something that is partially received from genes. But if the person grew up in an aggressive family environment, had friends who displayed aggressive behavior, then that person will eventually grow up themselves to be very aggressive. It is noted here that even though certain behavioral traits may be partially heritable, it only manifests if that particular trait is nurtured.

The example of nature vs. nurture and its effect on behavior was shown in an article in Wall Street Journal, where they showed that environmental sensitivity can be attributed to genetic factors. The scientists divided people into two groups – orchids and dandelions. The orchid were people whose behavior was more susceptible to environmental factors, while it was much less significant in the dandelions. This was because of the variation in their genes in the amount of dopamine (such as DRD4) produced in their bodies. The orchids had a lower amount of this dopamine produced, which is why they were more prone to stress and get distracted easily with the slightest stimulus. The dandelions on the other hand, had an ample amount of this hormone produced, which is why they tend to learn better from adversity and are comparatively more stable.

The ability to pick up different speech sounds, and learn a language, amongst other things is genetic and is seen in all babies, irrespective of their environmental conditions. Physical and intellectual skills like learning particular subjects, or ability to play certain sports, or being artistic may be partially heritable, but it needs to be cultivated over time for it to manifest the individual.

Based on Bowlby’s Theory of Attachment, it is suggested that the bond between mother and child is innate, that is it is genetically inherited. Another propagator of the naturalist view was Chomsky, who suggested that the language is gained through the use of an inherited Language Acquisition Device (LAD).

Skinner on the other hand, believed that language was acquired by imitation and the cultivation of the same in an individual’s respective environment. Certain genetic factors can also decide how an individual interacts with their environment. For example, a child who is by nature inhibited, may be shy or introverted when it comes to social interaction, while those who are predisposed to be extroverted may be sociable, friendly, and will actively seek social bonds. Conversely, when the environment is more extreme, they play a greater role in a person’s development. For example even if a child is naturally intelligent, but is brought up in an environment of deprivation, he may not grow up to reach his full intellectual capacity. During prenatal development, if a child is exposed to drugs or other harmful substances through intake by the mother, then he may be susceptible to diseases, disorders, or may grow up with deformities. So what started out as an environmental factor turned into a genetic predisposition.

When it comes to personality traits, the Twin Studies is one of the major factors that can be used as reference. In this study, identical twins who were rared apart show a more similar personality that those reared together, or a random selection of people. Identical twins are more similar that fraternal twins, while natural siblings are more alike than adopted siblings. This suggests that personality is partially heritable, but eventually nurture plays a role in how these traits are shaped. Adopted Studies on the other hand showed that even when these siblings are reared in the same family environment, by adulthood, there is almost no similarity in their personality, which suggests the manifestation of nature.

In the case of intelligence, the same adoptive studies revealed certain occurrences. These show that environmental factors have a bigger hand in molding childhood IQ. But by adulthood, this correlation is almost null. They revealed that by adulthood, the difference in IQ among adoptive siblings may make them seem like strangers, despite the shared environment they grew up in. In natural siblings on the other hand, there was a correlation of about 0.6. In the twin studies, it showed that identical twin who were reared apart had a higher correlation (about 0.86) while fraternal twins raised together had just 0.6 heritability. Adoptive siblings on the other had a 0.0 heritability of IQ. This seems to suggest that nature plays a bigger role in shaping intelligence.

But we cannot rule out nurture entirely. For example, nutrition plays an important role in shaping intelligence. If a child is not put on a proper diet from the get-go, then their neural connections and pathways get disrupted, which leaves then mentally challenged. Stress and exposure to toxins can also impede intellectual growth. As mentioned earlier, a person may have innate talents, but if they were not brought up in the right surroundings, their potentials may never be realized. Conversely even someone with lower genetic inheritance of intellect may be nurtured in a rich educational environment and may be able to supersede his original potential.

After going through this you may wonder what then really affects our behavior. The fact is, that both go hand-in-hand and one cannot work without interacting with the other and thus both play more or less an equal role in shaping how you behave. An interesting thing to note is that the nature versus nurture is a factor present in animals too. Let us see how.


CONCLUSION

Sex-linked biology and gender relations, as well as the concepts of race and ethnicity, require conceptual clarity in order to determine the interactive influences of each in giving rise to health differentials. To narrowly focus on such concepts impedes an appreciation of the rich variety among humans, however attention must be given to these and other categories in order to conduct meaningful research assessing the impact on health of interactions among social, behavioral, and genetic factors. For example, although a consistent genetic effect across racial groups can result in genetic variants with a common biological effect, that effect can be modified by both environmental exposures and the overall admixture of the population. The challenge is to parse out how health outcomes are influenced by genetic variations, behavioral and cultural practices, and social environments independently and as they interact with each others, while recognizing that sex, gender, race, and ethnicity may play important roles in their own right and because of their social meanings.


Watch the video: Factors That Influence the Growth and Development of a Child (May 2022).


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