social sciences

Personality: genetic factors?

Using methods such as twin studies, we can infer that personality is, at least partially, genetically determined. There is, however, also an environmental component, which is also imperative to personality formation. In these studies, the Big Five personality test is often used to look at how it develops over time.

Big Five personality traits
Using twin studies, researchers have found that there seems to be a genetic component to personality traits (Jang, Livesley, & Vemon, 1996). Twin studies are often used to study the effects of genes, identical twins and fraternal are then compared on these traits. One of the most used personality factor models is the Big Five, the five traits are openness, conscientiousness, extraversion, agreeableness, and neuroticism.

Instability and extraversion
Another group of researchers also looked at twin studies to find out what the genetic component is of psychosocial instability and psychosocial extraversion. They found that half of the variation in these traits could be explained by genetics (Floderus-Myrhed,  Pedersen,  & Rasmuson, 1980). Simply put,  the other half might be explained by environmental factors. So personality is partially shaped by the situations we go through in life.

Personality disorders
However, apart from regular personality traits, one can also study personality disorders. These are detrimental as they affect behavior or thinking processes in a negative manner. Which means it can influence daily functioning for an individual. These types of disorders have also found to be heritable, though most of the variance can be attributed to environmental factors (Jang,  Livesley, Vernon,  & Jackson, 1996).

Anxiety/social phobia
It has been found that fear of negative evaluation, which is one of the characteristics of anxiety or social phobia have genetic influences as well (Stein, Jang, & Livesley, 2002).

Job satisfaction
Another team of researchers looked at the genetic components that influence job satisfaction. They used the aforementioned five factor model of personality and the positive affectivity–negative affectivity personality test. The positive affectivity–negative affectivity assess what type of emotions (negative or positive) respondents tend to experience. Using these two tests, they found that both of these constructs determined job satisfaction.  The positive affectivity–negative affectivity construct explained most of the variance in job satisfaction (Ilies, & Judge, 2003).

Floderus-Myrhed, B., Pedersen, N., & Rasmuson, I. (1980). Assessment of heritability for personality, based on a short-form of the Eysenck Personality Inventory: A study of 12,898 twin pairs. Behavior genetics10(2), 153-162.

Jang, K. L., Livesley, W. J., & Vemon, P. A. (1996). Heritability of the big five personality dimensions and their facets: a twin study. Journal of personality, 64(3), 577-592.

Jang, K. L., Livesley, W. J., Vernon, P. A., & Jackson, D. N. (1996). Heritability of personality disorder traits: a twin study. Acta Psychiatrica Scandinavica94(6), 438-444.

Ilies, R., & Judge, T. A. (2003). On the heritability of job satisfaction: The mediating role of personality. Journal of Applied psychology88(4), 750.

Stein, M. B., Jang, K. L., & Livesley, W. J. (2002). Heritability of social anxiety-related concerns and personality characteristics: a twin study. The Journal of nervous and mental disease190(4), 219-224.

social sciences

Are you genetically similar to your friends?

People pick their friends based on several factors including proximity and similarity. Proximity is of importance because we prefer stimuli we see often as opposed to stimuli we’re not familiar with (mere-exposure effect). This principle also holds for friendships. Apart from starting friendships with people, we’re regularly exposed to, it is also easier to maintain relationships with those nearby us. Similarity is imperative for creating bonds, as it gives us topics to talk about and ideas to agree on. We also understand those who are similar to us a lot better. But could these similarities among you and your friends indicate that you might also be genetically similar?

Research has found that this seems to be the case by looking at a sample of adolescents in the United States. Guo (2006) found that there might be a genetic basis for trait-specific similarities between friends. To analyze genetic differences and similarities, identical (monozygotic) and non-identical (dizygotic) twins are always added to the sample. Interestingly, Guo also found that identical twins were more likely to list their twin as their best friend, compared to non-identical twins. Maybe we can speculate here that because identical twins share more genetic similarities, they might have more trait-specific similarities, which is an important factor in friendship.

Looking at more twin studies, we can see the same result for partner choice as well. Rushton and Bons (2005) compared identical twins to non-identical twins. They found that identical twins had friends and spouses similar to that of their co-twin. Again, we can speculate that there must be an underlying genetic effect for friend and partner choice.

Guo, G. (2006). Genetic similarity shared by best friends among adolescents. Twin Research and Human Genetics, 9(01), 113-121.

Philippe Rushton, J., & Ann Bons, T. (2005). Mate Choice and Friendship in Twins: Evidence for Genetic Similarity. Psychological Science, 16(7), 555-559.

social sciences

Cheating from an evolutionary prespective

It often seems as if people want to create a division between men and women based on their behavior. And one of the much talked about aspects is relationships. I have been a part of several discussions on whether men or women cheat more on their significant other. From an evolutionary perspective, there is a lot to be said about the implications of cheating for men and women. 

However I’m not going to speculate on who cheats more, but the consequences of cheating for each individual. Buss, Larsen, Westen, and Semmelroth (1992) carried out a fascinating study on this topic. First of all, they address certain differences between males and females, which include pregnancy and parental certainty. In our species as many other species, females are at risk of getting pregnant through sex. So from that point on invest many resources in their offspring, whereas males can often easily abandon their offspring. Though the success of our species has been attributed to the fact that males throughout stuck around to care for their offspring (compared to other species, unfortunately this is not necessarily standard even in modern times). A problem for males is that they cannot be sure (without a DNA test) whether their offspring is genetically theirs.

Differences between men and women
All of these assumptions create a framework that can possibly explain jealousy caused by a cheating partner. As females find emotional cheating to be worse, whereas men can’t stand sexual cheating. Although I would like to point out that both sexes have issues with all types of cheating, there are significant differences in the degree of. These differences would have made a lot of sense in the Pleistocene era, the period of time when early humans transitioned to modern humans. The issue with emotional cheating for a female is that a male might get emotionally invested in another female. But for the offspring it would be beneficial for the male would be involved in their upbringing. Thus it would be problematic for the (pregnant) female to lose the parental investment from the male. For males it is a slightly different story, they seem to be more concerned with sexual cheating. The reasoning behind this is that the female could end up getting pregnant by a different male. And if a male were to be invested in offspring that isn’t theirs – he would be investing in survival and transfer of another individual’s genetics. This perspective is from a ‘selfish gene perspective’ in which a lot of strategies seemed to be based around the survival of one’s own genes through reproduction.

However not only do we invest in the survival of our own genes through reproduction, and making sure our offspring survives by caring and protecting them. We can also protect genes that aren’t in our offspring or in us, yet they are still ‘our’ genes as well. Our siblings approximately share 50% of our genes. This is because we get 50% from our fathers and 50% from our mothers, this seems to be the general rule. Though recent research has found that we might be getting just a little more from our fathers (Crowley et al, 2015). And following the same principle we share 12,5% of our genes with our cousins. Based on all of these assumptions were more likely to help out those we share genetic similarities with because it would guarantee survival of part of our own genes. This is referred to as kin selection, these heroic acts of saving relatives could even be in situations that decrease the chances of one’s own survival.

Issues with an evolutionary perspective
A lot is to be said about taking an evolutionary perspective. First of all, while some are convinced that we still carry the biologically programmed mechanisms that, for instance, make us feel jealous in certain situations, it is an oversimplification. There are many factors that influence our thoughts, behaviors, and emotions. And the current scientific paradigm does not propose genetic determinism, in the sense that genes are exclusively responsible for the aforementioned constructs. Environmental influences are known to influence these three major components as well, it is most likely an interaction between the two. Second of all, we no longer live in the Pleistocene era, we live in an epoch that comes after that, called Holocene. Although evolution takes a lot of time, we have several examples from the last 10,000 years. On example is lactase persistence, humans have become able to digest lactose, especially in certain regions in the world. These regions were involved in domestication of animals and consuming milk. This is referred to as gene/culture co-evolution, where culture and genetics are both susceptible to evolution and mutation. Third, in line with the previous argument, in many regions of the world, lifestyles have dramatically changed. Not only heterosexual couples take care of offspring, however this idea alone might have been an oversimplification for the Pleistocene epoch. Children are often looked after by many more or different people than (biological) parents.

Buss, D. M., Larsen, R. J., Westen, D., & Semmelroth, J. (1992). Sex differences in jealousy: Evolution, physiology, and psychology. Psychological science, 3(4), 251-255.

Crowley, J. J., Zhabotynsky, V., Sun, W., Huang, S., Pakatci, I. K., Kim, Y., … & Yun, Z. (2015). Analyses of allele-specific gene expression in highly divergent mouse crosses identifies pervasive allelic imbalance. Nature genetics, 47(4), 353-360.