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How much influence does toxoplasmosis have on personality and intelligence?

How much influence does toxoplasmosis have on personality and intelligence?


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Latent toxoplasmosis affects up to 1/3 of the human population and up to 40% of the population in Australia. I have heard that latent toxoplasmosis has many significant undesirable effects on personality, such as decreased novelty-seeking behaviour, and decreased intelligence quotient.

While these changes are statistically significant, I'm wondering if anyone knows the magnitude of these personality and cognitive changes, since a statistically significant result doesn't necessarily imply that there is a large difference in personality between those who are infected and those who aren't infected. Also, can one succeed in an academic career path if one becomes infected with toxoplasmosis?


I believe its the other way around - humans may engage in riskier and more novel behavior when infected… which is the most interesting part of the story. Its not cut and dried, but I think its quite possible that risky behavior increases.

T. gondii is a parasite whose typical life cycle includes both mice and cats as hosts. The transmission involves the mice being eaten by a cat. Mice infected with T gondii will tend to lose some interest in being sheltered in close spaces and wander out into open spaces. They also lose their fear of cats. That is a permanent change even if the mice are cleared of the parasite.

Other animals, such as humans are secondary hosts - they can become infected by handling or close proximity to cat feces, who have a nearly 50% (45.6%) infection rate themselves. As a result toxoplasmosis is very common in humans.

Toxoplasmosis has been found to increase novelty seeking and increases risk seeking behavior at least in men. Its been shown to contribute to higher automotive accident rates, schitzophrenia and suicide.

Thus, the men were more likely to disregard rules and were more expedient, suspicious, jealous, and dogmatic. The personality of infected women, by contrast, showed higher warmth and higher superego strength (factors A and G on Cattell's 16PF), suggesting that they were more warm hearted, outgoing, conscientious, persistent, and moralistic. Both men and women had significantly higher apprehension (factor O) compared with the uninfected controls.

The correlation between toxoplasmosis and lower intelligence is a matter of debate, at least in this review I cite. Its still not clear whether it is a sociological correlation - do smart people just handle their cat poo more carefully or not at all? This more recent study shows that some factors might make infected humans more intelligent and some researchers see toxoplasmosis as a transformative factor in humans ability to generate and use technologies.

I do see those links suggesting less risky behavior too. Some say that the increase in traffic accidents is related to lower muscular coordination for instance. There is evidence on both sides, but looking at what T gondii does to mice, I would bet that some risk behavior will increase. As such, I'd guess that researchers as such might have a slightly higher rate of toxoplasmosis, but maybe you will do a study and help figure this out!

That being said - anyone who tries to link a single phenomenon; host-parasite interactions; a drug; a gene; a mutation to a phenotype with a simple description is definitely oversimplifying. The mapping from biological activity to english (or any other language) is hopefully conscious of the caveats of such talk.


It is my understanding that toxoplasmosis can increase productivity and the brain's ability to understand things. It is when there is a toxo flare that behaviors can become irrational and angry. Knowing this can help as well as being in touch with when you are experiencing a flare. Knowing what range you have, if its active, and what supportives you will need to get it under control should help.

The Revolving Therapies have the best chance of putting folks into remission according to the following information:

*Together with the result of the checklist, the significantly positive Toxoplasma LTT overruled the result of the antibody assays and justified prescribing a combination therapy from the beginning on. This resulted in a good amelioration of symptoms. When the effect of this therapy decreased after 10 days, the significant toxoplasma LTT result backed the decision for a Revolving Therapy, which finally led to a very good remission of all symptoms. *

https://en.toxoplasmachronic.com/2-faelle-mit-positivem-ltt?fbclid=IwAR2VknK1asw1OoWuedVpRi_TOGaxjDsf6LxWoLM7HKPfxZaHe3AIf1YI5N4


Is intelligence determined by genetics?

Like most aspects of human behavior and cognition, intelligence is a complex trait that is influenced by both genetic and environmental factors.

Intelligence is challenging to study, in part because it can be defined and measured in different ways. Most definitions of intelligence include the ability to learn from experiences and adapt to changing environments. Elements of intelligence include the ability to reason, plan, solve problems, think abstractly, and understand complex ideas. Many studies rely on a measure of intelligence called the intelligence quotient (IQ).

Researchers have conducted many studies to look for genes that influence intelligence. Many of these studies have focused on similarities and differences in IQ within families, particularly looking at adopted children and twins. These studies suggest that genetic factors underlie about 50 percent of the difference in intelligence among individuals. Other studies have examined variations across the entire genomes of many people (an approach called genome-wide association studies or GWAS) to determine whether any specific areas of the genome are associated with IQ. These studies have not conclusively identified any genes that have major roles in differences in intelligence. It is likely that a large number of genes are involved, each of which makes only a small contribution to a person’s intelligence.

Intelligence is also strongly influenced by the environment. Factors related to a child’s home environment and parenting, education and availability of learning resources, and nutrition, among others, all contribute to intelligence. A person’s environment and genes influence each other, and it can be challenging to tease apart the effects of the environment from those of genetics. For example, if a child’s IQ is similar to that of his or her parents, is that similarity due to genetic factors passed down from parent to child, to shared environmental factors, or (most likely) to a combination of both? It is clear that both environmental and genetic factors play a part in determining intelligence.


Does Birth Order Affect Personality?

In spite of sharing genes and environments, siblings are often not as similar in nature as one might think. But where do the supposed differences come from? Alfred Adler, a 19th- and early 20th-century Austrian psychotherapist and founder of individual psychology, suspected that birth order leads to differences in siblings.

Adler considered firstborns to be neurotic, because they don&rsquot have to share their parents for years and are essentially dethroned once a sibling comes along. He also considered oldest children dutiful and sometimes conservative. According to Adler, the youngest children are ambitious, while middle children are optimally positioned in the family and are characterized by emotional stability. Adler himself was the second of seven children.

American psychologist Frank J. Sulloway, who, in the mid-1990s, combed history books for leading figures who were firstborns and rebellious ones who were born later, saw a similar trend. Among the later borns, he found lateral thinkers and revolutionaries, such as Charles Darwin, Karl Marx and Mahatma Gandhi. Among firstborns, he discovered leaders such as Joseph Stalin and Benito Mussolini. His explanation? Every child occupies a certain niche within the family and then uses his or her own strategies to master life. Firstborn and single children had less reason to quarrel with the status quo and identify more strongly with the worldview of their fathers and mothers. Younger siblings are less sure of their parents&rsquo view and therefore more often choose alternative paths in life.

Such categorizations are popular because they&rsquore rather intuitive, and one can always find an example of the sensible big sister or the rebellious young brother in their circle of acquaintances. As such, Adler&rsquos words still appear regularly in educational guides and continue to reverberate in the minds of parents.

Furthermore, some studies confirmed the idea that sibling position can shape personality. For example, a 1968 study showed that, compared with later borns, first borns are less likely to participate in dangerous sports because of fears of physical injury. And a 1980 study of 170 female and 142 male undergraduates showed lower anxiety and higher ego in firstborns, as measured by the Howarth Personality Questionnaire. At times, however, these investigations used questionable methods. For example, members of the same family were often asked to assess themselves in terms of extraversion, openness to experiences, conscientiousness, tolerance and neuroticism. The catch is these surveys were conducted at only one point in time. The older siblings were therefore not only born first but also simply older. It has long been known that adolescents become more conscientious as they age. This trend could account for a large part of the results. Another methodological flaw was that only one person judged his or her own personality and that of his or her siblings. This detail is important because self-perception and the perception of others can sometimes differ considerably. In addition, the test subjects may have subconsciously incorporated the cliché of dutiful older siblings and cosmopolitan later borns into their evaluation and could have thus brought about the expected result themselves.

Meanwhile scientists who analyzed large, transnational data and compared different families with each other have found the effect of sibling succession on personality disappears almost completely. Researchers led by psychologist Julia Rohrer of the University of Leipzig in Germany evaluated data from more than 20,000 interviewees from Germany, the U.K. and the U.S. They compared the personality profiles of siblings but also of people with different birth orders who had never met. The Leipzig psychologists did not discover any systematic differences in personality.

In such studies, researchers must be particularly cautious because, in addition to age, the size of one&rsquos family is another factor that&rsquos intertwined with sibling position. A child from a family of four has a 50 percent chance of being a firstborn the more siblings, the lower the probability. For example, the fact that many astronauts are firstborns does not necessarily speak to the special qualities of those born first. It&rsquos likely that many astronauts come from smaller families. To better understand these influences, Rohrer and her team controlled forthe number of siblings. That&rsquos because when there are more of them, there are more later borns. So the researchers hypothesized later borns may more often appear in families of lower socioeconomic classes&mdashwhich could account for differences between children of different-sized families.

The larger the sample, the more likely even very small effects will be detected. For example, in a 2015 study, which included 377,000 high school students, psychologist Rodica Damian and her colleague Brent W. Roberts, both then at the University of Illinois at Urbana-Champaign discovered that firstborns tended to be more conscientious, extraverted and willing to lead. Contrary to expectations, they were also more tolerant and emotionally stable than adolescents with older siblings. Yet the differences were very small, and the researchers concluded that the importance that is generally attached to sibling position in shaping one&rsquos character is exaggerated.

&ldquoIt is quite possible that the position in the sibling sequence shapes the personality&mdashbut not in every family in the same way,&rdquo says Frank Spinath, a psychologist at Saarland University in Germany. &ldquoIn other words, there may be an influence but not a systematic one. Nevertheless, other influences weigh more heavily when it comes to the differences in character of siblings. In addition to genes, the so-called undivided environment also plays a role. For siblings who grow up in the same family, this includes the respective circle of friends, for example.&rdquo Further, parents do not treat their children the same regardless of their birth rank. Studies show that parents react sensitively to the innate temperament of their offspring and adapt their upbringing accordingly.

Damian&rsquos study also found that on average, firstborns enjoy a small IQ advantage over their younger siblings. Those born first also tend to complete their education with a higher degree and opt for traditionally prestigious careers, such as medicine or engineering.

How does this intellectual advantage come about? Adler may be right that the undivided attention given to the first child in early life promotes cognitive abilities. This advantage is already apparent by the age of two. Norwegian researchers Petter Kristensen and Tor Bjerkedal cleverly showed that the difference in intelligence is not linked to biological factors (some had suspected it might be related to physical conditions during pregnancy). They tested children whose older siblings had died early. The researchers&rsquo assumption was that although these children were biologically younger siblings, they assumed the role of the firstborn in the family. Compared with other younger siblings, they achieved better results in intelligence tests.


Studying Personality Using Molecular Genetics

In addition to the use of behavioural genetics, our understanding of the role of biology in personality recently has been dramatically increased through the use of molecular genetics, which is the study of which genes are associated with which personality traits (Goldsmith et al., 2003 Strachan & Read, 1999). These advances have occurred as a result of new knowledge about the structure of human DNA made possible through the Human Genome Project and related work that has identified the genes in the human body (Human Genome Project, 2010). Molecular genetics researchers have also developed new techniques that allow them to find the locations of genes within chromosomes and to identify the effects those genes have when activated or deactivated.

Figure 12.12 Laboratory Mice. These “knockout” mice are participating in studies in which some of their genes have been deactivated to determine the influence of the genes on behaviour.

One approach that can be used in animals, usually in laboratory mice, is the knockout study (as shown in Figure 12.12, “Laboratory Mice”). In this approach the researchers use specialized techniques to remove or modify the influence of a gene in a line of knockout mice (Crusio, Goldowitz, Holmes, & Wolfer, 2009). The researchers harvest embryonic stem cells from mouse embryos and then modify the DNA of the cells. The DNA is created so that the action of certain genes will be eliminated or knocked out. The cells are then injected into the embryos of other mice that are implanted into the uteruses of living female mice. When these animals are born, they are studied to see whether their behaviour differs from a control group of normal animals. Research has found that removing or changing genes in mice can affect their anxiety, aggression, learning, and socialization patterns.

In humans, a molecular genetics study normally begins with the collection of a DNA sample from the participants in the study, usually by taking some cells from the inner surface of the cheek. In the lab, the DNA is extracted from the sampled cells and is combined with a solution containing a marker for the particular genes of interest as well as a fluorescent dye. If the gene is present in the DNA of the individual, then the solution will bind to that gene and activate the dye. The more the gene is expressed, the stronger the reaction.

In one common approach, DNA is collected from people who have a particular personality characteristic and also from people who do not. The DNA of the two groups is compared to see which genes differ between them. These studies are now able to compare thousands of genes at the same time. Research using molecular genetics has found genes associated with a variety of personality traits including novelty-seeking (Ekelund, Lichtermann, Järvelin, & Peltonen, 1999), attention-deficit/hyperactivity disorder (Waldman & Gizer, 2006), and smoking behaviour (Thorgeirsson et al., 2008).


Are You Born With a Certain Personality?

While everyone (including you) gushes over your newborn, no matter how deliriously exhausted you are postpartum you may find yourself wondering “What will my baby’s personality be like? Will they be a quiet baby who doesn’t cry often? Or, will my baby be chronically cranky, up all night, and always ‘hangry,’ such as…dare I say it…myself?!”

“Children are born with some early signs of their personality, called temperament,” explains Dr. Jessica Myszak, a Glenville, Illinois-based child psychologist and the director of The Help and Healing Center. “These are usually evident in the first few days to weeks of life. It’s estimated that 20-60% of temperament is due to genetics. There are three types of temperament: easy, difficult, or slow-to-warm-up.”

According to Dr. Myszak, temperament influences how children interact with their environment, and it involves the following:

  • Their activity level - how much they engage in physical activity
  • How they approach situations - whether they jump into new situations without looking back or take longer to become comfortable
  • Regularity - how consistently they eat, sleep and use the bathroom
  • Adaptability - how easily they can adjust to new situations
  • Intensity - their energy level
  • Mood - whether they tend to be pleasant or less friendly
  • Attention span - how long they can attend to a task
  • Distractibility - how easily they can be distracted
  • Sensory threshold - how much of a sound, or a touch, or other sensory input is needed before a child responds

How common 'cat parasite' gets into human brain and influences human behavior

Toxoplasma is a common 'cat parasite', and has previously been in the spotlight owing to its observed effect on risk-taking and other human behaviours. To some extent, it has also been associated with mental illness. A study led by researchers from Karolinska Institutet in Sweden now demonstrates for the first time how the parasite enters the brain to influence its host.

"We believe that this knowledge may be important for the further understanding of complex interactions in some major public health issues, that modern science still hasn't been able to explain fully," says Antonio Barragan, researcher at the Center for Infectious Medicine at Karolinska Institutet and the Swedish Institute for Communicable Disease Control. "At the same time, it's important to emphasize that humans have lived with this parasite for many millennia, so today's carriers of Toxoplasma need not be particularly worried."

The current study, which is published in the scientific journal PLoS Pathogens, was led by Dr Barragan and conducted together with researchers at Uppsala University.

Toxoplasmosis is caused by the extremely common Toxoplasma gondii parasite. Between 30 and 50 per cent of the global population is thought to be infected, and an estimated twenty per cent or so of people in Sweden. The infection is also found in animals, especially domestic cats. People contract the parasite mostly by eating the poorly cooked flesh of infected animals or through contact with cat faeces. The infection causes mild flu-like symptoms in adults and otherwise healthy people before entering a chronic and dormant phase, which has previously been regarded as symptom-free. It is, however, known that toxoplasmosis in the brain can be fatal in people with depleted immune defence and in fetuses, which can be infected through the mother. Because of this risk, pregnant women are recommended to avoid contact with cat litter trays.

A number of studies have been presented in recent years showing that the toxoplasmosis parasite affects its host even during the dormant phase. It has, for example, already been observed that rats become unafraid of cats and even attracted by their scent, which makes them easy prey. This has been interpreted as the parasite assuring its survival and propagation, since the consumed rat then infects the cat, which through its faces can infect the food that other rats might then proceed to eat. A number of studies also confirm that mental diseases like schizophrenia, depression and anxiety syndrome are more common in people with toxoplasmosis, while others suggest that toxoplasmosis can influence how extroverted, aggressive or risk-inclined an individual's behaviour is.

"We've not looked at behavioural changes in people infected with toxoplasma, as that's been dealt with by previous studies," says Dr Barragan. "Instead, we've shown for the first time how the parasite behaves in the body of its host, by which I mean how it enters the brain and manipulates the host by taking over one of the brain's neurotransmitters."

In one laboratory experiment, human dendritic cells were infected with toxoplasma. After infection, the cells, which are a key component of the immune defence, started secreting the signal substance GABA. In another experiment on live mice, the team was able to trace the movement of infected dendritic cells in the body after introducing the parasite into the brain, from where it spread and continued to affect the GABA system.

GABA is a signal substance that, amongst other effects, inhibits the sensation of fear and anxiety. Disturbances of the GABA system are seen in people with depression, schizophrenia, bipolar diseases, anxiety syndrome and other mental diseases.

"For toxoplasma to make cells in the immune defence secrete GABA was as surprising as it was unexpected, and is very clever of the parasite," says Dr Barragan. "It would now be worth studying the links that exist between toxoplasmosis, the GABA systems and major public health threats."


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.


Intelligence: More Nature Than Nurture?

While showing an impressive growth prenatally, the human brain is not completed at birth. There is considerable brain growth during childhood with dynamic changes taking place in the human brain throughout life, probably for adaptation to our environments.

Evidence is accumulating that brain structure is under considerable genetic influence [Peper et al., 2007]. Puberty, the transitional phase from childhood into adulthood, involves changes in brain morphology that may be essential to optimal adult functioning. Around the onset of puberty gray matter volume starts to decrease, while white matter volume is still increasing [Giedd et al., 1999].

Recent findings have shown, that variation in total gray and white matter volume of the adult human brain is primarily (70--90%) genetically determined [Baare et al, 2001] and in a recent magnetic resonance imaging (MRI) brain study with 45 monozygotic and 61 dizygotic 9-year-old twin-pairs, and their 87 full siblings also high heritabilities have been found [Peper et al, in preparation]. Thus, while environmental influences may play a role in later stages during puberty, around the onset of puberty brain volumes are already highly heritable.

Hilleke Hulshoff Pol presents persuasive evidence how genetic factors influence the brain structure opening new insights into the reciprocal gene-environment developmental pathways.

Genetic influences

Twin studies have also shown that genetic effects vary regionally within the brain, with high heritabilities of frontal lobe volumes (90--95%), moderate estimates in the hippocampus (40--69%), and environmental factors influencing several medial brain areas.

However, the mechanisms by which interaction between genes and environment occur throughout life as well as dynamics of brain structure and its association with brain functioning still remain unknown. Twin and family studies and newly evolving genetic approaches start to give us a glimpse as to which genes and (interacting) environmental influences are shaping our brains.

Brain structure -- measured macroscopically using MRI -- and the dynamic changes therein, have a functional relevance.

Studies revealed that total brain volume is positively correlated with general intelligence. In healthy subjects, the level of intellectual functioning has been positively associated with whole brain, gray, and white matter volumes [Thompson et al, 2001 Posthuma et al, 2002]. More focally, several brain areas were found to be correlated with intelligence. Interestingly, it was also shown that the trajectory changes in cortical thickness throughout adolescence are associated with the level of intelligence.

Furthermore, a common set of genes may also cause the association between brain structure and cognitive functions. However, in elderly twins, the associations between frontotemporal brain volumes and executive function were found to be because of common environmental influences shared by twins from the same family [Carmelli et al., 2002].

These results point to the possibility that overlapping sets of genes or common environmental influences cause variation in two distinct phenotypes. It might be, for example, that a higher level of cognitive functioning leads a person to select an environment that also increases brain size. The genetic influence on brain size then simply reflects the genetic influences on cognition. Thus, the specific mechanism, pathways, and genes that are involved in human brain morphology and its association with cognitive functions remain elusive.

Although genetic effects on morphology of specific gray matter areas in the brain have been studied, the heritability of focal white matter was unknown until recently. Similarly, it was unresolved whether there is a common genetic origin of focal gray matter and white matter structures with intelligence. In our study involving 54 monozygotic and 58 dizygotic twin pairs and their 34 singleton siblings, verbal, and performal intelligence were found to share a common genetic origin with an anatomical neural network involving the frontal, occipital, and parahippocampal gray matter and connecting white matter of the superior occipitofrontal fascicle, and the corpus callosum [Hulshoff Pol et al., 2006].

For the genetic analyses, structural equation modeling and voxel-based morphometry were used. To explore the common genetic origin of focal gray matter and white matter areas with intelligence, cross-trait/cross-twin correlations were obtained in which the focal gray matter and white matter densities of each twin are correlated with the psychometric intelligence quotient of his/her cotwin.

The results of this study indicate that genes significantly influence white matter density of the superior occipitofrontal fascicle, corpus callosum, optic radiation, and corticospinal tract, as well as gray matter density of the medial frontal, superior frontal, superior temporal, occipital, postcentral, posterior cingulate, and parahippocampal cortices. Moreover, the results show that intelligence shares a common genetic origin with superior occipitofrontal, callosal, and left optical radiation white matter and frontal, occipital, and parahippocampal gray matter (phenotypic correlations up to 0.35).

These findings point to a neural network that shares a common genetic origin with human intelligence. Thus, it seems that the individual variation in morphology of areas involved in attention, language, visual, and emotional processing, as well as in sensorimotor processing are strongly genetically influenced.

In addition, unique environmental factors influenced vast gray matter and white matter areas surrounding the lateral ventricles (up to 0.50). This finding coincides with the significant environmental influences on lateral ventricle volume [common (0.58) and unique (0.42) with no significant contributions of genes] that was reported previously in this twin sample [Baaré et al., 2001].

Clinical implications

Considering the high heritabilities for global brain volumes and particular focal brain densities and thicknesses, the search for genes that are involved in brain growth, aging, and brain structure maintenance is important. Such knowledge can help us understand normal developmental and age-associated changes in individual variation in brain functioning.

Moreover, it enhances our knowledge of individual variation in brain functioning and facilitates the interpretation of the morphological changes found in psychiatric disorders such as schizophrenia [van Haren et al., 2007]. Also, it allows future efforts to find particular genes responsible for brain structures to be concentrated in areas that are under considerable genetic influence [Hulshoff Pol et al., 2006].

A genetic approach to find genes involved in brain structure that has been applied in several studies is that of diseases with a clear genetic etiology such as Huntington's disease, Down syndrome, Williams syndrome, and Velocardiofacial syndrome. A review reveals for these diseases besides disease specific brain changes, decreases in total brain, white matter, and hippocampus volumes, irrespective of the genes and/or chromosomes involved. This suggests that many genes are probably involved in the individual variation of these measures [Peper et al., in press].

It is important to investigate which environmental factors have an influence on the expression of genes (as found in DNA-methylation). Additionally, the study of interaction between genes and environmental factors is warranted. Furthermore, the simultaneous effects of multiple genes and possibly the interaction among genes, also needs investigation as the high heritability of a complex quantitative phenotype such as brain volume cannot be explained by a single-gene polymorphism.

MRI studies in twins indicate that, given the basic additive genetic model, overall brain volume in adulthood is highly heritable.

To test for influences of genetic, common, and unique environmental factors or interactions between genetic and environmental influences. twin studies carried out in large and more homogenous samples, analyzed with advanced quantitative genetic methods are needed.

To investigate the stability of genetic and environmental influences onto functional neural networks in human brain longitudinal twin studies in childhood as well as in adulthood are needed since brain volume changes dynamically throughout life.

New brain-imaging methods, such as DTI-fiber tracking and resting state functional MRI, allow to study the heritability of neural networks underlying brain functioning.

These new methods, in coherence with new genetic approaches, will enable us to further disentangle which genes and environmental factors and interactions therein influence human brain structure throughout life.

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Hulshoff Pol HE, Schnack HG, Posthuma D, Mandl RC, Baare WF, van Oel C, van Haren NE, Collins L, Evans AC, Amunts K, Burgel U, Zilles K, de Geus EJ, Boomsma DI, Kahn RS. Genetic contributions to human brain morphology and intelligence. J Neurosci 200626:10235-10242

Carmelli D, Reed T, DeCarli C. A bivariate genetic analysis of cerebral white matter hyperintensities and cognitive performance in elderly male twins. Neurobiol Aging 200223:413--420

Baaré WFC, Hulshoff Pol HE, Boomsma DI, Posthuma D, de Geus EJC, Schnack HG, van Haren NEM, van Oel CJ, Kahn RS. Quantitative genetic modeling of variation in human brain morphology. Cereb Cortex 200111:816--824

van Haren NE, Hulshoff Pol HE, Schnack HG, Cahn W, Mandl RC, Collins DL, Evans AC, Kahn RS. Focal Gray Matter Changes in Schizophrenia across the Course of the Illness: A 5-Year Follow-Up Study. Neuropsychopharmacology 200732:2057-2066

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Thompson PM, Cannon TD, Narr KL, van Erp T, Poutanen VP,Huttunen M, Lonnqvist J, Standertskjold-Nordenstam CG, Kaprio J, Khaledy M, Dail R, Zoumalan CI, Toga AW. Genetic influences on brain structure. Nat Neurosci20014:1253--1258

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What Factors Influence Intelligence

There are only two factors that affect intelligence: genes and the environment. Since then, there has been a constant tug of war between the importance of “nature or nurture”, to assess a person’s mental and physical prowess. Whereas a person may inherit a certain set of genes, what happens to him/her depends upon environmental factors. This can be reflected in the case of identical twins, where IQs (intelligence quotients) can be quite similar, but if they are raised apart, differences in levels become much wider. On the other hand, fraternal twins have less similarity siblings raised in the same household will have IQs that are like adopted children, raised together in the same environment.

Without doubt, genes play an important part in influencing intelligence. Even before the baby is born, a mother’s age, health, nutrition, smoking, and drinking habits can greatly affect the fetus. Hereditary factors like blood type, mother’s red blood cell count, and even RH ( a protein found in red blood cells) compatibility to the baby can affect its intelligence. A mother’s history of number of pregnancies, and the time between pregnancies also come into play. Even excessive exposure to X-rays or large amounts of lead can be strikes against a baby’s intelligence.

It is believed breastfed babies rank higher on IQ tests at the age of 6, than their counterparts who drank milk from a bottle. Birth order also affects IQ. It is believed every successive sibling will rank .7 lower on their test scores. This is also reflected in scholastic achievement. However, the argument might be the oldest and youngest of siblings usually receive more parental attention, resulting in more or less motivation than middle children. Birth order appears to place a part in their intelligence development and growth.

There is no evidence that having good nutrition factors into childhood intelligence, but a prolonged period of malnutrition can affect IQ. Children who purportedly eat breakfast every day, score ten points higher on an IQ test than those who do not. This might constitute good argument for children not to go to school hungry eat their breakfast every morning to learn better at school.

Early years – Growing up in a spacious house and in a good neighborhood have profound effects on a child’s mental and emotional development. Parental background such as education, occupation, and family income also play a large role in the factoring of IQ.

Quality of toys, books, magazines external stimuli such as travel going to an organized institution even taking music or dance lessons can affect a child’s intelligence. Quality of the school does not appear to affect intelligence, but school attendance does play a major part, especially during elementary school. Stability appears to be an important portion of a child’s upbringing when it comes to intelligence.

While there are questions concerning the interplay between heredity and environment, there are also theories that categorize different kinds of intelligence. Some scientists believe in a single general ability while others claim there are many and multiple intelligences: verbal, visual, kinesthetic (muscular movement), logic, social, musical, intrapersonal (within oneself), and natural (having the ability to be at one with nature).

Age also factors into intelligence, as the very young have the ability to do abstract thinking and reasoning, without the previous experience of education or learning. At this young age, they can create strategies for problem-solving and solving puzzles as well.

However, as one ages, this kind of abstract thinking decreases after the age of 30-40. People who are older tend to think along the terms of past learning and past experience. This intelligence makes use of facts, new knowledge and cumulative understanding in order to learn. This kind of learning, reasoning, and solving problems continues throughout adulthood.

In addition, there is a new intelligence to be added to the list of multiple intelligences, and that is emotional intelligence. Emotional intelligence can be a genetic ability from birth or it can be learned or strengthened by environmental elements. In 1990, a couple of scientists/psychologists determined that emotional intelligence is an offshoot of social intelligence – having the ability to observe one’s and other people’s feelings or emotions. This is an ability to discriminate or guide one’s emotional thinking and therefore one’s actions.

Since there are many facets of intelligence, all kinds of environmental factors can affect the genetic makeup of any given individual.


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