Genetic Explanations

If 50% of the differences between our personalities and intelligence is Genetic, is the other 50% Nurture?

It is always wise before getting involved in a discussion of genetics and human behaviour to say a number of things up front before launching into a confusing analysis. I’ll argue that in the developed world nurture makes little difference to who or what we are.

  1. Evolution and genetics does not care a jot about human happiness, fairness or equality.  Evolution’s only driver is to successfully reproduce genes and move them forward in time inside the cosy environment of a living organism (e.g. us). We are a disposable container to further the interest of our genes.  We die, they don’t.
  2. Any behaviour endowed by the genes, which make us more likely to survive and have more children, will by definition cause more of that type of behaviour to be inherited in the subsequent generation.
  3. Evolution moves along at a glacial pace.  One tick of the evolutionary clock is approximately 250,000 years.  We are therefore very similar to our ancestors of 50,000 years ago.  Recent technical and social advances are largely irrelevant to our genetic make.
  4. Evolutionary genetics can go a very long way to explaining human behaviour.  Each species is hard wired to behave in a very specific way and this has been shaped by the mechanism of evolution my natural selection.  i.e. it explains the is of human behaviour.
  5. Any discussion about the ought of human behaviour cannot and should not be decided (or justified) by evolution.  Morals, ethics, the rule of law and civilised, evidence based debate are the only mechanisms for reaching a consensus of how we ought to behave.
  6. For evolution to work there needs to be variation in behaviour so that natural selection can do its work.  Each generation has random variation and mutation (some beneficial, most harmful) from which to choose the best characteristics using natural selection.
  7. That said, I believe the human species evolved as a social, altruistic species and it is very much in our interest to act in this way.

Much of the work on genes versus environment (nature vs. nurture) has relied on identical twin studies and adoption studies.  Identical twins share identical genes, so it is very useful to follow the progress of identical twins that have been separated at birth and brought up in different environments.  In this way we can measure the effect of genes, irrespective of environment.  This type of study can be compared with adoption studies, where we can compare the life of a child brought up in a specific environment, which is very different to that of their genetic parents.

There is an enormous amount of data from these studies, which are now backed up with studies of Molecular and Mendelian Genetics.

The conclusion is that at a population level, on average, something like 50% of the differences between our intelligence and personalities is genetically determined.  (I’ve laid a trap here for those who believe that nurture is the overwhelming influence in our life.  Careful you don’t fall into it!).

Many people seem to believe that talent (e.g. the ability to hit a tennis ball) may be genetically determined, but drive and ambition is not.  What evidence do they have?  The ability to concentrate, a desire for wealth and power, the desire to be caring and altruistic could be equally genetically determined.  We all know people with talent and no drive, and also sadly, people with drive and no talent.  To be wildly successful we need both.  Can drive and ambition really be learned?

Many other types of behaviour are typically attributed to learned behaviour by flawed sociological studies.  i.e. it is assumed the behaviour is learned from parents or close social group.  e.g. the majority of people who sexually abuse their children were sexually abused by their relatives, implying learned behaviour.  People who smack their children were smacked themselves, implying learned behaviour.  The income of a person is most likely to be predicted by the income of their parents (i.e. as a proxy for talent and drive), implying learned behaviour.  In no cases are these sociological studies investigated for a genetic component.

Individuals inherit genes from their parents.  Could it be that part of the behaviour is inherited through the genes?  i.e. genes for abusive behaviour, genes for violent behaviour, genes for drive and talent…..

Mix our knowledge of genetics with one of the most passionate and time consuming aspects of human behaviour, i.e. finding a mate, and you have a very powerful natural force. Talented, motivated, women generally seek and marry talented, motivated, men. They then generally have talented, motivated children. i.e. they cluster the genes responsible for these talented, motivated characteristics into certain sections of society.  As these characteristics generally lead to higher earning potential they are more likely cluster in the affluent parts of society.  Consequently talented, motivated children are not equally spread in our society, assuming we have a certain level of social mobility.  Remember I’m talking about is not ought.  This process is called assortative mating.  The identical twin / adoption studies have concluded that since the 1950s upbringing makes virtually no difference to our social status by the age of 35.  i.e. society is mobile enough in developed countries.   This makes sense, as any environmental influence is short lived, whereas we have our genes for life.

Now for the trap laid for the nurture lovers.  If 50% of our differences are genetic, then the other 50% must be nurture and open to social and political intervention, right?

The term “genetically determined” is very narrow.  It refers to traits and behaviours which are inherited through the genes.  Nurture is everything else.  For example we know that the hormonal, nutritional and chemical environment of a developing child in the womb has non-negligible effect on its future life.  What was interesting about the identical twin studies was not only what made them the same (their genes) but what made them different.  Identical twins share the same womb, same parents, same wealth, same schools, same teachers and are still different.  It is difficult to imagine genes controlling the exact wiring of the human brain as it develops.  Could it be that whilst the overall brain structure is genetically pre-determined, whether a neurone in a developing brain zigs to the left, or zags to the right before connecting with a neighbour is in fact random?  Maybe one identical twin gets bitten by a dog, or catches ‘flu or only gets the bottom bunk bed and these trivial experiences add up to a large difference overall.  Whatever the reason it seems that much of what we describe as nurture is also not open to manipulation by political social policies.

Also, if nurture was a dominant force, all siblings in a family would be the very similar on the basis they share a similar upbringing.  Anybody with more than one child knows that this is nonsense!

Finally to a point on meritocracy.  It is in our interest as a species that we have the best people in the right jobs.  We all benefit.  There should be no discrimination based on colour, class or sex.  But this includes positive discrimination too.  We should not be giving people a leg up because a perceived injustice unless we can prove beyond doubt that they really have been disadvantaged.

Many believe Private schools, well-connected parents and other things too subtle to mention all shape success. Few would disagree that the State has a role to play in dismantling some of these advantages to create a more level playing field.  But the part of nurture that is open to political manipulation is a very  small compared to everything else in a country that is already economically developed and relatively socially mobile.  We must learn to manage our expectations as to how much can be achieved with political meddling.  Unless that State wants to dictate with whom we marry?

Assortative mating ensures that genes for talent and motivation would be clustered in affluent parts of society.   However this is only a tendency.  Vast talent will be found in non-affluent parts of society because there are many more of them.  History tells us that well meaning meddling by the State merely consumes vast financial resources with no benefit, partly because we try to save everybody.  We would do better to spot talent and motivation early and nurture it, wherever it comes from. Concentrate our resources where we can make a difference.  i.e. targeted State intervention.

Who we are and what we become in a socially mobile, developed society seems to be a mixture of genes and luck with a little nurture thrown in. The best way to ensure success in life is to choose your parents with great care.  It is unfair.  Remember is not ought.

Further  Listening:

Intelligence: Born Smart, Born Equal, Born Different Three BBC Podcasts on the genetics of intelligence.

What makes some children smarter than others?  Professor Robert Plomin talks to Jim Al-Khalili about what makes some people smarter than others and why he’s fed up with the genetics of intelligence being ignored.


One thought on “If 50% of the differences between our personalities and intelligence is Genetic, is the other 50% Nurture?

  1. Wayward says:

    Some thoughts:

    Some thoughts:

    – Completely disagree with the happiness part in the 1st bullet point. I think happiness is THE driving force in evolution.
    – Altruism might be inheritable but so might be selfishness. I don’t think altruism is an ideal state. Personally, I think it makes more sense that there is an equilibrium between the two that has a great deal of volatility reflected in the population. Also, personalities are inheritable I think as well.
    – Selective pressure in humans stopped pretty early on in history. It did occur a little bit after the Paleolithic Period but most occurred at that time supposedly.
    – I disagree that studies show motivation is inheritable. I do think it may be true but the research isn’t clear. I might be wrong but the research was conducted in a school environment which really doesn’t indicate motivation.

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