Genetics and their influence on behavior, brain and society

All individual psychological differences are moderately to substantially heritable

"Psychological researchers typically distinguish five major domains of individual differences in human behavior: cognitive abilities, personality, social attitudes, psychological interests, and psychopathology. [...] In this article we [...] review behavioral genetic findings in all five domains. We conclude that there is now strong evidence that virtually all individual psychological differences, when reliably measured, are moderately to substantially heritable."

(Bouchard, Thomas J., and Matt McGue. "Genetic and environmental influences on human psychological differences." Journal of neurobiology 54.1 (2003): 4-45.)

DNA defines number of androgen receptors in brain

"Many factors influence how androgens impact brain functioning. Of course, some of these factors involve the actual prevalence of androgens in the brain during crucial periods of development (Kimura, 1992; Nordeen, Nordeen, Sengelaub, & Arnold, 1985). Another factor involves so-called androgen receptors (ARs). Without these receptors, the prevalence of androgens is largely inconsequential (La Spada, Wilson, Lubahn, Harding, & Fischbeck, 1991; Sato et al., 2004). The number of ARs is in turn determined by what are known as CAG repeats in the androgen receptor (AR) gene (located on the X chromosome, of which males only have one). The more CAG repeats on the X chromosome, the fewer the number of ARs an individual will have (Allen, Zoghbi, Moseley, Rosenblatt, & Belmont, 1992; Giovannucci et al., 1997). The number of CAG repeats in the AR determining gene is likely to play an important role in the ability of androgens to influence criminality and related behaviors (such as psychopathy).
Recent evidence pertaining to the above reasoning has been encouraging. A study conducted in India involving over five hundred men, roughly half of whom were convicted of rape. Evidence from
this study revealed that the rapists had significantly shorter CAG repeats in their AR genes than control males (Rajender et al., 2008). Also, a Chinese study found that the length of the AR gene repeats was significantly shorter among violent criminals than among the non-criminal males (Cheng, Hong, Liao, & Tsai, 2006). Findings from both of these reports suggest that male criminals, particularly those with assaultive tendencies, have unusually short CAG repeats in their AR genes relative to males in general. Furthermore, research has shown that the number of CAG repeats in AR genes is inversely associated with childhood conduct disorders and other forms of externalizing behavior among boys (Aluja, García, Blanch, & Fibla, 2011; Comings, Chen, Wu, & Muhleman, 1999)."

(Ellis, Lee, and Anthony W. Hoskin. "The evolutionary neuroandrogenic theory of criminal behavior expanded." Aggression and violent behavior 24 (2015): 61-74.)

HOX genes and influence on gonad, fingers and digit ratios

"The differentiation of gonads, fingers, and toes is influenced by HOXA and HOXD genes. Therefore variation in the development of the gonads, and their fetal products such as testosterone, may be reflected in the morphology of the fingers and toes. One trait, the relative length of the second and fourth digits (2D:4D), shows sex differences (lower values in males) which are determined early, and 2D:4D has been found to correlate with fetal growth, sperm counts, family size, autism, myocardial infarction, and breast cancer. HOX genes are highly conserved in mammals and they influence the differentiation of all the fingers and toes. We suggest that (a) 2D:4D and other ratios of finger and toe length show sex differences throughout the mammals including humans and mice, (b) finger and toe ratios correlate with sex determination, the fetal production of sex steroids, and fetal programming of disease, and (c) HOX gene influences on sex determination, the morphogenesis of the urinogenital system, fertility, haematopoiesis, and breast cancer suggests that finger and toe ratios in humans and mice may correlate with many sex dependent diseases."

(Manning, J. T., M. Callow, and P. E. Bundred. "Finger and toe ratios in humans and mice: implications for the aetiology of diseases influenced by HOX genes." Medical Hypotheses 60.3 (2003): 340-343.)

"[I]n 1984 the psychologist Sarnoff Mednick tapped into a Danish database of more than 14,000 adopted children, some of whom had been convicted of crimes. Mednick found that more than twice as many offenders convicted of property crimes, such as breaking and entering, had a biological father who was a criminal, compared with those who had an adopted criminal father; the proportion was even higher for repeat offenders. He concluded that criminal parents passed on ‘some factor’ to their biological children that made it likelier for them to become criminals, but noted that the correlation did not hold true when looking at violent crimes such as murder or assault.
Others have studied twins to look for hereditary similarities. Scientists who have analysed Denmark’s twin records have found a stronger correlation in crime between identical twins than between non-identical ones. That’s not to say that born criminals exist, according to Irving Gottesman, a psychologist at the University of Virginia who studied the Danish twin records; but heredity seemed to play a role in setting up the odds.[...]
[I]n 2011 [Avshalom Caspi and Terrie Moffitt of Duke University in North Carolina] published a finding (one among the hundreds they have produced over the years) that psychological assessments of self-control in children as young as three can predict whether a child will become a criminal in his or her 30s. They were able to reach that conclusion only after compiling the data of more than 1,000 people who had been tracked from early childhood to adulthood.[...]
While one gene does not equal one behaviour, for instance, patterns in thousands of genes can interact with thousands of behaviours in a constantly changing human environment. One study of fruit flies bred for aggression found partial links to 80 different genes. It’s also become known that gene expression is not a one-way street: while genes might affect a person’s body or even behaviour, the person’s environment can affect genetic expression. In one of their studies undertaken in Dunedin, Moffit and her post-doctoral student Idan Shalev found that 10-year-olds who experienced violence showed the kind of wear and tear in their DNA normally associated with ageing. All this means that, while it’s possible that a particular gene deficiency might have something to do with violent behaviour, it’s ludicrous to say that it directly caused it.
The same is true of brain structure and function. In recent years, researchers have learned that just as the brain can set tendencies, experiences can influence how they’re expressed.[...]
Minus the clutter, if you look at the totality of peer-reviewed studies of the past several years, it’s hard not to come to the conclusion that biology plays some role in criminal behaviour, impossible to quantify. The new science of epigenetics proposes an interaction between environment and heredity, in which environmental factors (such as childhood abuse) can affect the expression of genes. In other words, the nature-nurture division that scientists have been arguing about for more than a century is narrowing, and might someday disappear. Genes and brain structure do not represent a simple on-off switch that determines a person’s behaviour but, as some studies show, they can indicate a vulnerability.[...]
[Adrian Raine, professor of psychology, psychiatry and criminology at the University of Pennsylvania] has been studying brain scans for decades, and he has come up with a kind of grand unified theory of violence. He describes it with the phrase ‘from genes to brain to antisocial behaviour’. Certain gene abnormalities can lead to structural brain abnormalities that lead to emotional and cognitive abnormalities (such as poor impulse control) that can lead to anti-social behaviour. At the same time, he writes, early life experiences – including maternal neglect, poor nutrition, or being surrounded by gang violence – can feed into the cycle."

(source: "The inheritance of crime", by Douglas Starr, professor of journalism at Boston University, where he is co-director of the Center for Science and Medical Journalism. published on Aeon, retrieved 26-7-2016)

"Your genes may influence how sensitive you are to emotional information, according to new research by a UBC neuroscientist. [...] The gene in question is ADRA2b, which influences the neurotransmitter norepinephrine. [...] "We thought, from our previous research, that people with the deletion variant would probably show this emotionally enhanced vividness, and they did more than we would even have predicted, [...]."

(source: How your brain reacts to emotional information is influenced by your genes)

"Scientists have confirmed that variations in [the GABRB3] gene [... are] linked to differences in empathy levels in the general population."

(source: Study confirms a gene linked to Asperger Syndrome and empathy)

"Intellectual faculties are the sum of many factors, the majority of which are genetic and inherited from parents." (Dr. Sébastien Jacquemont, geneticist, clinical researcher at CHU Sainte-Justine and professor at the University of Montreal)

(source: Twenty-five-point drop in IQ caused by lack of gene copy, accessed 2016-01-28)

"In this study, the Japanese researchers determined that ​PX-RICS is most likely the gene responsible for autism-like symptoms in Jacobsen syndrome. To do this, they performed several well-established tests that measure common autism symptoms -- anti-social behavior, repetitive activities and inflexible adherence to routines. As compared to normal mice, mice lacking PX-RICS spent less time on social activities (e.g., nose-to-nose sniffing and huddling) and were more apathetic or avoidant when approached by a stimulator mouse. PX-RICS-deficient mice also spent more than twice as much time on repetitive behaviors such as self-grooming and digging than normal mice. In addition, mice lacking PX-RICS more closely adhered to a previously established habit and were less able to adapt their behavior in novel situations."

(Mouse model yields possible treatment for autism-like symptoms in rare disease, Sciencedaily, retrieved 17-3-2016)

"We were surprised by certain behaviors that showed a genetic influence, such as religiosity [and] social attitudes," said Nancy Segal, an evolutionary psychologist at California State University, Fullerton, who was part of the study for nine years. "Those surprised us, because we thought those certainly must come from the family [environment]," Segal told Live Science. [...]
The Minnesota researchers found that about 70 percent of IQ variation across the twin population was due to genetic differences among people, and 30 percent was due to environmental differences. The finding received both praise and criticism, but an updated study in 2009 containing new sets of twins found a similar correlation between genetics and IQ.
Moreover, a study in 1990 found that genetics account for 50 percent of the religiosity among the population — in other words, both identical twins raised apart were more likely to be religious or to be not religious, compared with unrelated individuals."

(Source: LiveScience, retrieved 30-5-2016)

(source: "Insights From Identical Twins", http://learn.genetics.utah.edu/content/epigenetics/twins/, retrieved 30-5-2016)

Nature or Nurture? The Study of Twins | Nancy Segal and Stefan Molyneux

"[T]hey looked at the IQ scores of mothers who had given away their children for adoption. So they had the IQ score of the biological mom, the adopted away kid, and the adoptive parents of that kid. And you know who was more alike? The biological kid and the biological mom who were not together, as compared to the adoptive mom who had raised the adoptive child."

(Dr. Nancy L. Segal, B.A. degree in psychology (with distinction) and English literature from Boston University (1973), and M.A. (1974) and Ph.D. (1982) degrees in Social Sciences and Behavioral Sciences from the University of Chicago. She is currently Professor of Psychology at California State University, Fullerton (CSUF) and Director of the Twin Studies Center which she founded in 1991.)
(source: Youtube interview "Nature or Nurture? The Study of Twins | Nancy Segal and Stefan Molyneux", 36min18s)

More arborized cortical neurons (with more dentritic branches) make friendlier, more social brains

"Scientists investigated Williams syndrome or WS, a rare genetic condition caused by deletion of one copy of 25 contiguous genes on chromosome 7, out of an estimated 30,000 genes in the brain. [...] WS results in a host of medical problems as well as a specific heart defect. [...] Neurologically, [persons with the deletion] have developmental delays, with severe spatial deficits, yet relative strengths in language use and face processing.
'An interesting aspect is the typical hyper-social predisposition,' said study co-author Ursula Bellugi, EdD, director of the cognitive neuroscience lab at Salk and an adjunct professor at UC San Diego who has studied WS for years. 'Persons with the WS deletion tend to be overly friendly, overly trusting, drawn to strangers, yet anxious.' [...]
'I was fascinated on how a genetic defect, a tiny deletion in one of our chromosomes, could make us friendlier, more empathetic and more able to embrace our differences,' [co-senior study author Alysson] Muotri [PhD, associate professor of pediatrics and cellular and molecular medicine at UC San Diego School of Medicine], said. [...]
Cultured WS neurons have a distinct morphology. They are more arborized (treelike, with many dendritic branches) than neurons derived from typically developing individuals. "At the functional level, they make more synapses or connections to other neurons than what you would expect," said Muotri. "That might underlie the WS super-social aspect and their gregarious human brain, giving insights into autism and other disorders that affect the social brain." [...]
'One striking observation was that [the] cortical neurons in WS individuals are more complex than controls (typically developing children of same age). The morphological alterations that presumably appeared during WS gestation are kept postnatally,' [said Katerina Semendeferi, PhD, co-senior author and professor at UC San Diego Department of Anthropology.]"

(source: "Neurodevelopmental model of Williams syndrome offers insight into human social brain", SienceDaily, August 10 2016)