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Updated: Apr 15, 2019

I recently finished Robert Plomin's new book, blueprint how DNA makes us who we are. Plomin is a Professor of Behavioral genetics at Kings College London and is responsible for major advances in understanding the genetic basis of human personalities and behavior, based in large part in his studies of twins, particularly those separated at birth. Plomin's book is filled with fascinating factoids about the extent to which our personality traits are already baked into the pie at birth, so to speak, and is well worth a read. You've probably wondered, why it is that two people, raised in the same environment, by the same parents, can have such dramatically different life results. For instance, Bill Clinton and his brother Roger Clinton. Some people are able to overcome the most horrible childhood environment and achieve great success while others, raised with all the benefits of a superior environment, descend the social and economic ladder. Plomin's book helps to explain this paradox.

There is no shortage of conclusions which one can take away from Plomin's book and I'll cover just a few of the ones I found most interesting. There are many more in the book, a fascinating read.

The primary thrust of Plomin's book is that roughly about 50% of your personality is determined by your genes (although the percentage varies widely for each personality trait). Often these traits are assumed to be environmental, but twin studies reveal them to be in our genes. For instance, Plomin notes that: "Parental divorce is the best predictor of children's divorce, but this correlation, easily interpreted as environmental, is entirely due to genetics". (It is my opinion that the 50% number will eventually be adjusted higher, as what now appear to be traits shaped by the environment, will later be found to be "epigenetic", that is, caused by genes triggered by environmental factors).

Plomin continues, that even though the remaining 50% of our personality comes from environmental factors, these factors are completely random and, at this this time, at least, unknowable. Plomin states that "there is no evidence for shared environmental effects of growing up in the same family." Let that sink in. There are no child rearing practices which can be shown to effect the personality traits of the adult that the child grows to be. Worse yet, the environmental factors which actually do contribute to the personality of each twin appear to be completely random and are related to non-shared environmental factors. As a result, there are no parenting styles or social programs which can direct a person to a path substantially different than that mapped out by their genes (just as there is no amount of practice which could have transformed me into a star quarterback).

Plomin's book has come into a substantial amount of criticism, primarily from the left, as an apology for determinism, but he goes to great lengths, throughout the book, to emphasize that "Heritability describes what is but does not predict what could be ... High heritabilty of weight does not mean that there is nothing you can do about your weight." Another of the implications of Plomin's work is that certain social programs directed towards children, are largely useless, for accomplishing the purpose for which they are designed. "Both occupational status and income are substantially heritable, about 40 percent ... ". He goes on to note that the remaining 60 % attributable to environmental factors is largely random and thus, improving a person's income or status by changing their environment is "not within our grasp". This is not a popular message for those who are wedded to the concept of correcting "privilege" through social programs. On the other hand, early childhood programs may make a disadvantaged child's life more enjoyable and an argument can be made that these programs should exist just as a matter of human kindness.

It is ironic that these same critics seem to ignore Plomin's decidedly progressive policy recommendations, Plomin advances the theory that because people are born with different abilities "..we need to replace meritocracy with a just society. ... children dealt a lucky genetic hand have a better chance of doing well at school and getting a better job and making more money. This inequality in outcome is not going to be tackled indirectly through the educational system." Instead, Plomin favors a re-distributive tax system.

Although I strongly feel that no man has a right to another man's labor, I might support income redistribution as a replacement for the myriad assortment of ineffective social programs which currently plague us, with the added provisos that: (1) the poor make their own decisions as to how the redistributed money is spent instead of the funds being routed through a social services bureaucracy and (2) that in no event, should there be an economic incentive not to seek employment.

As Theodore Dalrymple observes:

  • "Charity given as of right, for that is what the welfare state does, favours the undeserving more than the deserving, in so far as the undeserving have a capacity and even talent for generating more neediness than the deserving ... The welfare state in fact dissolves the very notion of desert, because there is no requirement that a beneficiary prove he deserves what he is legally entitled to. And where what is given is given as of right, not only will a recipient feel no gratitude for it, but it must be given without compassion — that is, without regard to any individual’s actual situation. In the welfare state, the notion of a specially deserving case is prohibited, for it implies a distinction between the deserving and the undeserving."

If a "just society" requires income redistribution then it also requires that the deserving receive more than the non-deserving, if only for the purpose of discouraging behavior which is harmful to society.

The final big takeaway from Plomin's book, which I would like to discuss, is that each of our personality traits is not contained within the genetic code for a few genes, but instead within thousands. As Plomin puts it: "twenty-five years ago, everyone hunting for genes assumes that a handful of genes accounted for most of the heritability observed in twin studies. ... The [study] results tell a different story. For complex traits, no genes have been found that account for 5 per cent of the varience, not even 0.5 percent of the varience. The average effect sizes are in the order of 0.01 percent of the variance, which means that thousands of SNP associations will be needed to account for heritabilities of 50 per cent." What I find interesting about this, is that it implies that the total number of possible unique personalities which could exist, is an unfathomably large number. Many, many times larger than the number of people who have ever existed by an incredibly large margin. I wonder why evolution would provide for an almost infinite number of flavors of human personality? Why wouldn't a mere two or three hundred million personality types suffice? This also means that every person must be, in every sense of the word, a unique person, from the moment of conception. (This is one of those situations where the reader may mistakenly assume that I am making a judgement about abortion - I am not. I'm simply making a neutral observation).

If I had any objection to Plomin's book, it is that the book seems to ignore completely the role of positive and negative feedback in shaping a person's behavior. In fact, there seems to be a conspicuous lack of discussion of the fact that individual behavior is often the outcome of group pressures and consequently, there is no recognition that the way in which a person acts, can be a much different thing than the way a person is. In my opinion, not only is the tendency to respond to group pressure a genetic trait but, in addition, almost all group behavior and human culture is, in large part, a genetic construct.. The removal of almost all negative feedback for antisocial behavior in today's society has serious knock-on consequences. For instance, the removal, in California, of jail time for thefts under $500 has resulted in an explosion of thefts from cars in San Francisco. Just because you may have a genetic propensity to be a thief, does not mean that society cannot successfully encourage you not to steal. Just because you are not genetically predisposed to seek employment, does not mean that society cannot successfully encourage you to work. Just because you have a genetic propensity to be irresponsible, does not mean that society cannot successfully encourage responsibility.

Otherwise an excellent and highly informative book.

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