Is "sick" the right word?

 

Ted Bundy, 1978, State Archives of Florida (Wikicommons). Outwardly charming but zero concern for others.

 

Is sociopathy an illness? We often think so ... to the point that the word "sick" has taken on a strange secondary meaning. If we call a ruthless, self-seeking person "sick," we mean he should be shunned at all costs. We don't mean he should take an aspirin and get some rest.

Sociopathy doesn't look like a mental illness, being much less incapacitating than schizophrenia and most mental disorders. A sociopath can deal with other people well enough, perhaps too well. As Harpending and Sobus (2015) point out:

It is a psychopathology because of what sociopaths do to us, and it has significant legal, political, and moral consequences for all of us. Most criminals are probably sociopaths according to some definition (the figure of 80% is often quoted).

Sociopaths regularly present the following characteristics:

- onset before age 15, childhood hyperactivity, truancy, delinquency, disruption in school

- early and often aggressive sexual activity, marital histories of desertion, non-support, abandonment
- persistent lying, cheating, irresponsibility without visible shame
- sudden changes of plan, impulsiveness, unpredictability
- charm and a façade of sensitivity
- high mobility, vagrancy, use of aliases

Sociopaths follow a life strategy that is adaptive for themselves but ruinous for society. Harpending and Sobus (2015) argue that they succeed so well because they know how to manipulate social relationships to their advantage.  

Sociopathy is at least moderately heritable (Hicks et al., 2004). Interestingly, it seems to cluster with hysteria in first-degree relatives, with sociopathy being expressed in the males and hysteria in the females. Harpending and Sobus (2015) argue that "hysteria is the expression in females of the same genetic material that leads to sociopathy in males." In short, "sociopathy in females is the result of a greater dose of the genetic material that leads, in smaller doses, to hysteria, namely, hysteria is mild sociopathy." 

If sociopathy is adaptive, why does it affect only a minority of us? It seems that the rest of us have developed counter-strategies of looking for signs of sociopathy and expelling suspects from society ... and the gene pool. This is probably why sociopaths tend to be always on the move—if they stay too long with the same people, they risk being detected and dealt with.

Gene-culture coevolution

We adapt to our cultural environment as we do to our natural environment. More so in fact. The last 10,000 years have seen far more genetic change in our ancestors than the previous 100,000, this speeding up of evolution being driven by the entry of humans into an increasingly diverse range of cultural environments.

Sociopathy may thus propagate itself more easily in some cultures than in others, with the result that its incidence may likewise differ from one to another. In a small band of hunter-gatherers, a sociopath will not last long because he is always interacting with the same small group of people:

In a 1976 study anthropologist Jane M. Murphy, then at Harvard University found that an isolated group of Yupik-speaking Inuits near the Bering Strait had a term (kunlangeta) they used to describe "a man who ... repeatedly lies and cheats and steals things and ... takes sexual advantage of many women—someone who does not pay attention to reprimands and who is always being brought to the elders for punishment." When Murphy asked an Inuit what the group would typically do with a kunlangeta, he replied, "Somebody would have pushed him off the ice when nobody else was looking." (Lilienfeld and Arkowitz, 2007)

In a larger community, a sociopath may evade detection long enough to reproduce successfully and pass on his mental traits. Finally, in some cultures he can use his manipulative skills to dominate the community, becoming a "big man" and enjoying very good opportunities for reproduction.

This Pandora's Box was opened when humans gave up hunting and gathering and became farmers. First, farming supported a much larger population, so it became easier for sociopaths to move about from one group of unsuspecting people to another. Second, farming created a food surplus that powerful individuals could use to support underlings of various sorts: servants, soldiers, scribes, etc. There was thus a growing class of people who did not directly support themselves and whose existence depended on their ability to manipulate others.

Finally, in the tropical zone, farming greatly increased female reproductive autonomy. Through year-round farming, women could provide for themselves and their children with less male assistance. Men accordingly shifted their reproductive strategy from monogamy to polygyny, i.e., from providing for a wife and children to inseminating as many women as possible. This kind of cultural environment selected for male seducers and manipulators rather than male providers. Conversely, it selected for women who feel only an intermittent need for male companionship and who from time to time are able to coax assistance from people who are not so inclined:

Ethnographic descriptions of women who live in social contexts of low male parental investment portray women who are very demanding. Young women demand help from kin on behalf of children. When the help is not forthcoming the mothers often summarily dump or deposit the child or children at the door of a relative who (in their judgment) will not turn the children away. Women demand gifts from boyfriends for themselves. (Harpending and Draper, 1988)

In women, this selection pressure favors a condition known medically as Briquet's syndrome and more commonly as "hysteria":

When males are not good risks for parental investment, females will adjust their behavior accordingly. A common clinical characterization of Briquet's syndrome is a woman who exaggerates need, who demands high levels of attention and investment, who deceives herself and others as to her requirements. The strategy (learned or inherited) makes sense for a woman with high exposure to low investment males. These males, however, are so fickle and so mobile that they can be dunned only in the short run. (Harpending and Draper, 1988)

Sociopathic behavior, be it hysteria or full-blown sociopathy, is not favored in hunter-gatherers, since both sexes invest heavily in their offspring and in each other. The selection is for men and women who can bond strongly with one partner:

[...] abandonment of the pair bond by either partner is likely to be deadly for the offspring. Draper (manuscript) finds that men with more children spend more time hunting than men with fewer dependents; that is to say that more offspring are directly translated into more parental work for the male. Pennington and Harpending (manuscript) found that infant mortality among women who had more than one mate during their reproductive careers was nearly twice as great as infant mortality of women who had only one husband. [...] In societies of this type the contexts for the anti-social trait are unfavorable. There will be no pay-offs for anti-social behavior and the bearer of the trait will be readily detected and ostracized. (Harpending and Draper, 1988)

Strategy and counter-strategy

Sociopathy is therefore not an illness but a strategy. It has been least successful in small societies where both sexes invest heavily in care for their partners and offspring. It has been more successful in larger societies, particularly those where men invest less in partners and offspring. Indeed, because sociopathy does so well in such contexts, it may have hindered the development of larger and more complex societies.

In most large societies, people seek out and expel sociopaths from their local kin group and treat everyone else with suspicion. The result is the "amoral familialism" we see throughout much of the world. People prefer to deal with relatives, hire only relatives for their businesses and, as a rule, act morally only towards relatives. Thus, the high-trust environment of the family cannot extend to society in general. Among other things, this is why the market economy has failed to develop spontaneously over most of the world and over most of history. Without strong-armed government intervention (military pacification, police, courts, etc.), markets remain marketplaces—places of exchange that are highly localized in space and time. The market principle cannot spread to most economic transactions.

Some humans have resolved this problem by freeing themselves from the straitjacket of kinship, by adhering to social rules that apply to everyone, and by ruthlessly expelling rule breakers wherever they may be. This is the adaptation that Europeans have developed to the north and west of the Hajnal line. The relative weakness of kinship ties and, correspondingly, the relative strength of individualism favored a complex of psychological traits that may be summarized as follows:

- capacity to internalize punishment for disobedience of social rules (guilt proneness).

- capacity to simulate and then transfer to oneself the emotional states of other people, especially when such people are affected by rule-breaking either by oneself or by others (affective empathy).

- tendency to frame moral rules in universal, absolute terms, i.e., moral universalism and moral absolutism, as opposed to situational morality based on kinship. Rule-breakers are likewise condemned in absolute terms and may be expelled from the entire community, as opposed to being ostracized by close kin.

The above mental package brought Northwest Europeans closer than other humans to the threshold where one could escape the limitations of kinship and organize society along other lines, notably the market economy, the modern State, and political ideology. It thus became possible to meet the challenge of creating larger societies while ensuring compliance with social rules and a high degree of personal autonomy.

References 

Cooke, D.J. (2003). Cross-Cultural Aspects of Psychopathy, in T. Millon, E. Simonsen, M. Birket-Smith, and R.D. Davis (eds). Psychopathy: Antisocial, Criminal, and Violent Behavior, pp. 260-276, Guilford Press.

https://books.google.ca/books?hl=fr&lr=&id=LSiBsdxcGigC&oi=fnd&pg=PA260&dq=psychopathy+cross-cultural&ots=nnV3xh4mZZ&sig=FBW4rme_w0tj2REoHQJpqXXSB6Q#v=onepage&q=psychopathy%20cross-cultural&f=false 

Harpending, H. and P. Draper. (1988). Antisocial behavior and the other side of cultural evolution, in T. E. Moffitt and S.A. Mednick (eds). Biological contributions to crime causation, pp. 110-125, Boston: Nijhoff.

https://books.google.ca/books?hl=fr&lr=&id=Vw7tCAAAQBAJ&oi=fnd&pg=PA293&ots=44dHOZn08j&sig=-2vXa0210OA82u-9Y-HzeEWM-y4#v=onepage&q&f=false 

Harpending, H. and J. Sobus. (2015). Sociopathy as an adaptation, Ethology and Sociobiology, 8, 63-72

https://www.academia.edu/11700522/Sociopathy_as_an_adaptation 

Hicks, B.M., R.F. Krueger, W.G. Iacono, M. McGue, C.J. Patrick. (2004). Family transmission and heritability of externalizing disorders. A twin-family study, Archives of General Psychiatry, 61, 922-928.

http://archpsyc.jamanetwork.com/article.aspx?articleid=482057 

Lilienfeld, S.O. and H. Arkowitz. (2007). What "Psychopath" Means, Scientific American, 18, 90-91.

http://faculty.fortlewis.edu/burke_b/Abnormal/Abnormal%20Readings/Psychopathy.pdf

Getting the babes but not the babies

 

Still from the film Is Matrimony a Failure? (1922). Who's making more babies? "Good boys" or "bad boys"? Originally, the good boys were, thanks to parental monitoring of relations between single men and single women. The pendulum then swung toward the bad boys in the 1940s, only to swing back after the 1960s.

 

A recent Swedish study has found that "bad boys" are outbreeding "good boys":

Convicted criminal offenders had more children than individuals never convicted of a criminal offense. Criminal offenders also had more reproductive partners, were less often married, more likely to get remarried if ever married, and had more often contracted a sexually transmitted disease than non-offenders. Importantly, the increased reproductive success of criminals was explained by a fertility increase from having children with several different partners. (Yao et al., 2014)

This study has been much talked about, yet few people have noticed its one big flaw. Sweden has many citizens of foreign origin whose crime and fertility rates exceed those of the native population (Crime in Sweden, 2014; Landes, 2008). Reproductive success may thus correlate with criminality simply because both tend to be higher among non-natives than among natives. Admittedly, this alternate explanation had been foreseen by the authors of the study and they tried to correct for it:

We included variables potentially associated with both criminal and reproductive behavior as covariates. [...] Immigrant status has been associated with both rule breaking, primarily through associations with other familial and socioeconomic risk markers (Moehling & Piehl, 2009), and adherence to cultural norms influencing fertility and monogamy-related outcomes (Coleman, 2006). The migration register provided information on immigrant status defined as being born in Sweden or not. (Yao et al., 2014)

Unfortunately, country of birth is no longer a satisfactory proxy for cultural identity, at least not in Sweden's case. There is now a large Swedish-born population that self-identifies as Pakistani, Somali, or Afghan, including the youths who rioted in Malmö last year. The Swedish crime rate is influenced almost as much by the Swedish-born of foreign background as by the foreign-born:

During the period 1997-2001, 25% of the almost 1,520,000 offences for which a perpetrator was convicted were committed by people born in the Middle East or Eastern Europe, while almost 20% were committed by people with a foreign background who were born in Sweden. (Crime in Sweden, 2014)

If we could examine only people of Swedish descent, I doubt reproductive success would still correlate with criminality or, more exactly, with a tendency to "love and leave" one woman after another. Such a correlation used to exist in the U.S. but disappeared almost half a century ago. This was the conclusion of Jason Malloy and JayMan (2012) when they used General Social Survey data to find out the number of children fathered by monogamous men ("good boys") versus men who had several female sex partners ("bad boys"). It seems that the reproductive success of bad boys has varied a lot over time:

 

Men born before 1920 - courtship under parental supervision 

In this cohort, good boys were the top breeders. No need to think hard to find the reason. Any man wishing to meet a single woman, other than a prostitute, had to run a gauntlet of parental supervision. The preferred form of courtship was still "calling." If a woman struck your fancy, you could "call" on her at her home. If she and her parents were favorably impressed, you could come back for further visits and eventually start taking her out to social events. Otherwise, that would be the end of it. A more direct approach could get you in big trouble, as a reference book for American lawmakers explained in 1886:

The state should punish, not only treacherous inducements to incontinence or to unchastity when accompanied by the violation of particular duties, and the seduction of minors, or girls under sixteen, but also seduction when it assumes a character dangerous to the interests of the community. It is not the duty of the state to make the individual moral, or to protect her against temptations to immorality; but it should endeavor to prevent all acts of immorality calculated to poison family life and the life of the nation. (Lalor, 1886, vol.III, p. 211)

The concern here is not just venereal disease, but also a family's genetic heritage. In the 19th century, people believed that a part of their essence was reincarnated in their children and grandchildren. Their concern over sex was fueled not by irrational hang-ups but by a very rational desire to maintain the integrity of their family line. Bad boys threatened that integrity, and it was not for nothing that many ended up in jail ... or at the end of a rope.

 

Men born between 1920 and 1939 - rise of dating, illegitimacy, and adoption

In this cohort, bad boys were the top breeders. Parental supervision had slackened with the replacement of calling by dating, thus creating new opportunities for them to sow their seed. A sharp rise in illegitimacy led to a sharp rise in adoption:

[...] The period 1945 to 1974, the baby scoop era, saw rapid growth and acceptance of adoption as a means to build a family. Illegitimate births rose three-fold after World War II, as sexual mores changed. Simultaneously, the scientific community began to stress the dominance of nurture over genetics, chipping away at eugenic stigmas. In this environment, adoption became the obvious solution for both unwed mothers and infertile couples. (Adoption, 2014)

Adoption had previously been very rare. As late as 1923, only 2% of children without parental care ended up in adoptive homes, the others going to foster homes or orphanages (Adoption, 2014). And a large chunk of that 2% involved adoptions between related families. These statistics are mirrored by my family tree: whenever children were left with no provider, they would be adopted by an aunt or an uncle or placed in a foster home. In those days, changing your family identity was as unthinkable as changing your religion or nationality.

To deal with the surge of illegitimacy, progressive-minded people now turned toward a seemingly great idea. On the one hand, there were babies abandoned by deadbeat dads. On the other, there were middle-class families with loving homes. Why not transfer these babies from the dads who don't love them to the ones who can?

The 20th century is littered with great ideas that proved to be not so great. Adoption is no exception. One negative outcome, which could have been foreseen, is that adopted children tend to replicate the psychological profile of their biological fathers. In one study, Gibson (2009) notes:

Adoptees were more likely than genetic offspring to have ever received public assistance, been divorced or been arrested. They also completed fewer years of schooling and were more likely to have ever required professional treatment for mental health, alcohol and drug issues.

[...] This supports other research showing that, compared to genetic children, American adoptees have a higher overall risk of contact with mental health professionals, specifically for eating disorders, learning disabilities, personality disorders and attention deficit hyperactivity disorder [...] They also have lower achievement and more problems in school, abuse drugs and alcohol more, and fight with or lie to parents more than genetic children [...]

These problems are not due to adoptive parents shortchanging adoptees. In fact, the reverse seems true:

This study categorically fails to support the hypothesis that parents bias investment toward genetically related children. Every case of significant differential investment was biased toward adoptees. Parents were more likely to provide preschool, private tutoring, summer school, cars, rent, personal loans and time with sports to adopted children. (Gibson, 2009)

Adoption does seem to improve the behavior of these children. It lowers their risk of committing violent crime, although they remain just as likely to commit other offences:

The possibility that genetic factors are among the causes of criminal behavior was tested by comparing court convictions of 14,427 adoptees with those of their biological and adoptive parents. A statistically significant correlation was found between the adoptees and their biological parents for convictions of property crimes. This was not true with respect to violent crimes. There was no statistically significant correlation between adoptee and adoptive parent court convictions. Siblings adopted separately into different homes tended to be concordant for convictions, especially if the shared biological father also had a record of criminal behavior. (Mednick et al., 1984)

With respect to intellectual capacity, adoptees likewise seem to benefit from their new homes, although the benefit tends to wash out over time. When children with two white biological parents were adopted into white middle-class homes, they initially did somewhat better than their non-adopted siblings, as seen on IQ tests at the age of 7. By the age of 17, however, the situation had reversed, with the adoptees falling behind their non-adopted siblings in terms of IQ, GPA, class ranking, and school aptitude (Minnesota Transracial Adoption Study, 2014).

Clearly, adoptees are getting some benefit although the benefit is less than what some may think. It also comes at a price. When the family unit is reoriented toward social welfare goals, it can no longer serve its original purpose of perpetuating a genetic heritage.

 

Men born after 1939 - separation of sex from reproduction

In this cohort, good boys have once again been the top breeders. This might seem counterintuitive. After all, sexual morality has become even more liberal since the 1960s, and this change has paralleled a growing infatuation with thuggish males in popular culture. Yet something seems to have kept bad boys from translating their sexual success into reproductive success.

That "something" is easier access to contraception and ... Roe v. Wade. More and more good girls are making out with bad boys, but fewer and fewer are making babies with them.

Pro-lifers see this as proof that pro-choicers are secret eugenicists. I think it's just an unintended consequence. Paradoxically as it may seem, modern culture is favoring the reproduction of stable couples who plan for the long term and invest in their children. 

Just think. What is the core message of modern culture? It's live for today, live for yourself, and avoid long-term commitments, such as family and children. And who responds the most to that message? It's people whose time orientation is already focused on the present and who already invest as little as possible in their offspring. Modern culture is sterilizing those individuals who are most susceptible to its message.

And so, when it comes to having babies and raising them to adulthood, America's white middle class is slowly but surely closing in on first place (Frost, 2012).

 

Conclusion

Perhaps this is all for the best. What other choices are there? Conservative politicians talk a lot about traditional values, but not one in ten believe what they say. To judge by their personal lives, many seem happy with the current climate of sexual permissiveness. Anyhow, if conservatives really do try to turn back the clock, their efforts will be blocked by the libertarian right and the liberal left. And if they manage to outflank both groups, they'll be lucky to take us back to the policies and practices of the 1950s. Unfortunately, this is one case where half-measures will make things worse. We've come to where we are because of the 1950s. 

So what political option is left for someone like me? I wish to preserve our existing genetic heritage, if only because we don't fully understand what we are about to lose. If you feel the same way, the best course of action seems to be the present one of separating sex from reproduction. Call it "tactical liberalism" if you wish, but I see no other realistic alternative.

 

References 

"Adoption" (2014) Wikipedia

http://en.wikipedia.org/wiki/Adoption 

"Crime in Sweden" (2014). Wikipedia

http://en.wikipedia.org/wiki/Crime_in_Sweden  

Frost, P. (2012). Obama: White America's bogeyman? Evo and Proud, November 24

http://evoandproud.blogspot.ca/2012/11/obama-white-americas-bogeyman.html  

Gibson, K. (2009). Differential parental investment in families with both adopted and genetic children, Evolution and Human Behavior, 30, 184-189.

http://anthro.vancouver.wsu.edu/media/Course_files/anth-260-edward-h-hagen/evil_step-parents.pdf 

JayMan. (2012). Some guys get all the babes - not exactly, JayMan's Blog, November 8

http://jaymans.wordpress.com/2012/11/08/some-guys-get-all-the-babes-not-exactly/ 

Lalor, J.J. (1886). Cyclopaedia of Political Science, Political Economy, and of the Political History of the United States, Chicago: A.H. Andrews & Co.

http://books.google.ca/books?hl=fr&lr=&id=AsM6AAAAIAAJ&oi=fnd&pg=PA1&dq=Cyclopaedia+of+Political+Science,+Political+Economy,+and+of+the+Political+History+of+the+United+States&ots=VqItRo_7kY&sig=aL3srydNpIpMoKOlKnd5gXqnp0g#v=onepage&q=Cyclopaedia%20of%20Political%20Science%2C%20Political%20Economy%2C%20and%20of%20the%20Political%20History%20of%20the%20United%20States&f=false  

Landes, D. (2008). Higher birth rates among Sweden's foreign born, The Local, November 3

http://www.thelocal.se/20081103/15408

Mednick, S.A., W.F. Gabrielli Jr., & B. Hutchings. (1984). Genetic influences in criminal convictions: evidence from an adoption cohort, Science, 224, 891-894

http://www.sciencemag.org/content/224/4651/891.short  

"Minnesota Transracial Adoption Study" (2014), Wikipedia

http://www.sciencemag.org/content/224/4651/891.short

Yao, S., N. Langstrom, H. Temri, and H. Walum. (2014). Criminal offending as part of an alternative reproductive strategy: investigating evolutionary hypotheses using Swedish total population data, Evolution and Human Behavior, in press

http://www.ehbonline.org/article/S1090-5138%2814%2900077-4/abstract

A pathway to pro-social behavior

 

The digit ratio is the length of the index finger (2^nd finger) divided by the ring finger (4^th finger). It correlates with the degree of androgenization or estrogenization of fetal tissues, including the fetal brain. (source)

 

As small bands of hunter-gatherers gave way to larger and more complex societies of farmers and townsfolk, trusting relationships had to expand beyond the circle of close kin. This larger social environment posed a two-fold problem:

For trust to evolve our ancestors must have 1) overcome the incentive to defect when involved in cooperative activity, and 2) suppressed the proclivity to use violence to take resources from conspecifics, as is seen in nonhuman primates. (Gifford, 2013)

This in turn required "social rules of governance and implicit institutions that suppressed free riding, provided rules of orderly behavior that increased cooperation by making individual behavior predictable, and also protected the property rights of individuals" (Gifford, 2013).

But what, exactly, does one do with free riders and sociopaths? Traditionally, such people were excluded from society, either by ostracism or, in more serious cases, by execution. There was thus strong selection for pro-social behavior, i.e., acting honorably and peacefully with other members of society. This selection operated even when ostracism was far from permanent or total. Shunning, public shaming, or simply a bad reputation would hurt one's chances for survival and reproduction in many ways: reduced access to community goods, discrimination on the marriage market, reluctance by others to provide assistance, and so forth.

This process of selection had genetic consequences, since nearly all behavioral traits have a heritability of 40% plus or minus 20%. There was thus removal not only of antisocial individuals from society but also of antisocial predispositions from the gene pool. The corollary was that the gene pool became dominated by pro-social predispositions, particularly empathy, compliance with social rules, and high thresholds for expression of anger.

This evolution probably occurred incrementally through small changes at many genes. This is what we see with increases in human intellectual capacity, and it is probably a general rule for the evolution of complex traits. Big changes at single genes tend to have nasty side-effects elsewhere on the genome.

A recent paper has highlighted one possible evolutionary pathway: the relative degree of androgenization or estrogenization of the developing fetus (Branas-Garza et al., 2013). By varying the ratio of one to the other, it's possible to alter a wide range of behavioral tendencies. This prenatal priming of fetal tissues can be easily measured by the "digit ratio," i.e., the length of the index finger (2nd finger) divided by the length of the ring finger (4th finger). The lower your digit ratio, the more you have been androgenized before birth. The higher your digit ratio, the more you have been estrogenized before birth.

Branas-Garza et al. (2013) found that altruistic behavior is strongest among men with intermediate digit ratios:

We analyze the association between altruism in adults and the exposure to prenatal sex hormones, using the second-to-fourth digit ratio. We find an inverted U-shaped relation for left and right hands, which is very consistent for men and less systematic for women. Subjects with both high and low digit ratios give less than individuals with intermediate digit ratios. We repeat the exercise with the same subjects seven months later and find a similar association, even though subjects' behavior differs the second time they play the game.

Different environments favor different degrees of altruism. In one setting, an altruist may be admired and enjoy preferential access to community goods. In another, the same person may be ridiculed and ruthlessly exploited. Thus, according to the context, the right balance has to be struck between altruism and selfishness:

One possible interpretation of the above findings comes from stabilizing selection. Since sharing with others is socially beneficial, selfish individuals are socially excluded and their fitness affected negatively. If individuals who are exposed too much or too little do not share with others, there is an evolutionary pressure on these non-altruistic individuals, which in turn generates an indirect evolutionary pressures on the degree of exposure to prenatal sex hormones by raising survival probabilities of individuals with intermediate levels of exposure. This hypothesis is supported by observed distributions of 2D:4D in the literature, which are universally concentrated around the median values. (Branas-Garza et al., 2013)

From one population to the next, digit ratios tend to cluster around different means, perhaps because altruism has been favored or disfavored to different degrees. This social selection may have targeted other behavioral traits, notably thrill-seeking. Kornhuber et al. (2013) have found that low digit ratios are associated with video game addition. This kind of addiction may tap into a male need for risk and adventure, which may likewise have been more adaptive in some environments than in others.

 

References 

Brañas-Garza, P., J. Kovárík, L. Neyse (2013). Second-to-fourth digit ratio has a non-monotonic impact on altruism. PLoS ONE 8(4): e60419.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0060419 

Gifford Jr., A. (2013). Sociality, trust, kinship and cultural evolution, The Journal of Socio-Economics, 47, 218-227

http://www.csun.edu/~hceco001/Researchpapers/Researchpapers/socialityandtrust.pdf 

Kornhuber, J., E-M. Zenses, B. Lenz, C. Stoessel, P. Bouna-Pyrrou, et al. (2013). Low 2D:4D Values are associated with video game addiction. PLoS ONE 8(11): e79539.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0079539#pone-0079539-g002