Genetic Explanations, Liberty, Politics and Economics, Religion

Why homosexuality is natural – an evolutionary explanation

Since Aristotle, we have philosophised a scientific and moral order to the world.  A “natural order” or “utopia” to creation.  A way things were meant to be.  If we acted against this order then nature would be disrupted and chaos would ensue.  This pre-supposition was incorporated into the major religions where it is assumed that God had a plan for creation and that His plan was “designed” to be harmonious.  If we could only understand what God intended for the world then we would know how to behave. But only religion knew how we ought to behave according to God’s design, because only religion knew God’s mind. Religion therefore got involved with “moral teaching”, which was a code of behaviour that God had intended and endorsed.

So religion expropriated moral behaviour based on a belief in a “purpose” or “design” of nature.  Men were men, and women were women, and they were meant to marry and have children.

However, unlike Aristotle’s assertion and accepted religious doctrine, evolution does not provide an “ought” for nature.   There is no intention in evolution.  Genes have no intelligence or sentience.  They are inert, self-replicating, complex molecules that have evolved over 3,500,000,000 years to build intricate life-support machines around them (living organisms) that help them replicate themselves.  We humans are a disposable container to further the interest of our genes.  We die, they don’t.

Evolution works by natural selection.  Each generation of genes has small random variations and mutations (some beneficial, most harmful) from which nature chooses the best characteristics using natural selection.  The beneficial behaviours survive and are amplified in future generations and the unbeneficial behaviours dwindle or die out.

Genes merely cover their options by providing random variation to ensure that whatever the future environment may be, some of them will be adapted to take advantage of it.

Without this evolution could not occur and we would still be living primordial slime.

So massive climate change, asteroid attacks, disease and any number of previous natural disasters has not wiped out life on our planet.  It just changes which genes (and therefore which species) are best adapted for the new environment.

So there is no “ought” in evolution.  There is no “intent” or a way things were meant to be.

So nature naturally provides variation in human characteristics and behaviour.  We have variations in skin colour, variations in hair colour, variations in aggressive behaviour and variations in intelligence.  And yes, variations in sexuality.  Some people are gay, some are heterosexual, and some can be anywhere on the spectrum in between.  So homosexuality is as natural as red hair or black skin or blue eyes.

Studies have shown that homosexuality runs in families, leading most researchers to presume a genetic underpinning of sexual preference. However, no major gene for homosexuality has yet been found.   But whilst much variation is directly caused by genes, we know that some variation is only indirectly caused by genes.  Recent studies in epigenetics have found a plausible mechanism for human homosexuality.  Epi-marks constitute an extra layer of information attached to our genes’ backbones that regulates their expression. While genes hold the instructions, epi-marks direct how those instructions are carried out – when, where and how much a gene is expressed during development.

Sex-specific epi-marks produced in early fetal development protect each sex from the substantial natural variation in testosterone that occurs during later fetal development. Sex-specific epi-marks stop girl fetuses from being masculinised when they experience atypically high testosterone and vice versa for boy fetuses. Different epi-marks protect different sex-specific traits from being masculinised or feminised – some affect the genitals, others sexual identity, and yet others affect sexual partner preference.

Epi-marks are usually erased and produced anew each generation, but recent evidence demonstrates that they sometimes carry over between generations and thus can contribute to similarity among relatives, resembling the effect of shared genes.  When sex-specific epi-marks are transmitted across generations from fathers to daughters or mothers to sons, they may cause reversed effects, such as the feminisation of some traits in sons and similarly a partial masculinisation of daughters.

So this mechanism can affect a developing foetus’ response to hormones in the womb which may affect brain development and sexuality.  But how can a genetic trait that causes sexual preferences which will not result in pregnancy and children survive generation after generation?   The reason that many people think homosexuality is “unnatural” is because it denotes behaviour which does not result in any future generations.  Natural selection should ensure that genes for homosexuality will die out.  Many believe the fear of persecution caused many homosexuals to marry and have children in order to fit into society, thus propagating these genes into future generations.  However,  mathematical modeling demonstrates that genes coding for these epi-marks can easily spread in the population because they only rarely escape erasure causing homosexuality in the offspring.  Genetic transmission of epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality.

So our knowledge that homosexuality has a genetic basis, which is subject to evolution by natural selection, would lead us to predict that homosexuality would be rare.  This is verified by the  results of the third National Survey of Sexual Attitudes and Lifestyles recently published in The Lancet.   It shows that 7% of men have had some sort of same-sex “sexual experience” and only 4% had physical sex with a man.  The percentage of females who say they have had a sexual “experience”, including kissing, with another woman was 16% and the number admitting to having sex with another woman was 8%.  However there are good evolutionary reasons why we would predict that homosexual behaviour in women would be greater than in men.  (See blog:  Is there a bit of lesbianism in all women? )

Now that homosexuality is accepted in modern societies there is less pressure on homosexuals to marry and have children in order to “fit in” and avoid persecution.  This could mean that there will be less homosexuality in the future because if there are genes which code for homosexual behaviour they would become even less common.  However the recent research into epi-marks suggests that homosexuality will never disappear.  It will just remain rare.

Gay Marriage and Liberty

Genetic Explanations

Men and Women Evolved With Conflicting Interests – Why We don’t Always Get Along


For millennia human kind has believed in a “natural order”, or a “utopia” to creation.  A way things were meant to be.  Since Aristotle we have envisaged a scientific and moral order to the world.  If we acted against this order then nature would be disrupted and chaos would ensue.  This pre-supposition was incorporated into the major religions where it is assumed that God had a plan for creation and that plan was designed to be harmonious.  Consequently men and women are “designed” to live together in perfect harmony – if only we could work out how!

Darwinism, whilst accepting that men and women have many areas of common interest, also accepts that they will have areas of conflicting interest.

First let’s review the fundamentals of Darwinism:

  1. Evolution is not about survival of the species (e.g. humans) it is about survival of the genes. We are a disposable container that has evolved to ensure genes get moved forward in time. We die. They don’t.
  2. Any behaviour conferred by the genes, which increases the likelihood of having more offspring in any species, will ensure more of those genes are passed to the next generation.  Consequently that “successful” behaviour is propagated and amplified.   This is a natural selection of “beneficial” genes.
  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 makeup.
  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 by natural selection.  We don’t behave like cats or horses.
  5. 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.

Our male and female ancestors have had very different evolutionary pressure over the previous millions of years.

Human females have a pathetic ability to reproduce, having no more than a dozen pregnancies in their lifetime. Each pregnancy is life threatening and she will generally only produce offspring one at a time.  Human children are unusually vulnerable in infancy and take many years to reach maturity.  Women therefore engage in a long, energy sapping and life threatening investment in their children to ensure these (few) offspring reach childbearing age.  She must choose her mate with great care to ensure her offspring receive beneficial genes from the father, which in turn maximises the chance of her own genes prospering in the next generation.  It also means she must carefully and selflessly look after the few offspring she manages to produce. She (i.e. her genes) has no other choice.  Women evolved to be more nurturing.

Human males produce 250,000 sperm every second and their number of offspring is limited only by their opportunity to impregnate willing (or unwilling) females.   Two strategies would work to increase the number of their genes in the next generation.  1. Look after their offspring, nurture them and ensure they reach child bearing age (copy the only strategy available to women). 2. Spread their sperm as far and wide as possible, have thousands of offspring and hope that some reach childbearing age.  A third alternative is the best.  Do both.  Men invest almost nothing in child rearing so it makes sense for them to take huge risks to have the opportunity to reproduce.

Women will choose high social status men (a proxy for good genes) to ensure her own genes have a good chance of survival in future generations.  To prove high social status takes a bit longer so women tend to go for successful, older men (4 years older in the UK on average).

Men are programmed to advertise their success and achievements in order to attract a high social status mate.  Men will choose young, healthy, fertile (read attractive) women because their chosen mate primarily needs to be fit to survive 9 months of pregnancy and the years of childcare that follows.  Men have evolved to visually select a mate on this basis.  Women have evolved for millions of years with this pressure.  Women are therefore programmed to try to look young and attractive in order to find a suitable mate.  Much of this behaviour is hard wired, as is our sexuality and our urge to have sex with attractive members of the opposite sex.  Women also need to recognise these traits in their competition (other women).  Women easily know if another woman is attractive.

So whilst men and women have a mutual interest in looking after their mutual children, there are areas of conflicting interest.  As women can have few offspring it is in her genes’ interests to ensure the father spends all his time and energy looking after her children.  She will also feel an overwhelming urge to nurture her children.  Her genes have no other choice.  The father’s genes’ interests are better served by spending much of his time seeking different partners – particularly young, healthy and fertile (attractive) partners.  Women are more likely to seek commitment from a mate.  Men are more likely to be reluctant to give it.  Men will prefer younger sexual partners which over time act against the interests of his initial, older partners.

But some women are very attracted to totally inappropriate men who clearly act against her own interest.  The handsome, philandering, unreliable, lovable rogue.  Why?  Consider the scenario where a high social status male has a child with a particular woman and then leaves her and philanders his way around the world irresponsibly having hundreds of children with other women.  This is not good for the woman or her child.  But if this woman has a son which survives and inherits his father’s behaviour she will get many more of her own genes into future generations.  About 8% of the men in a large region of Asia have Genghis Khan’s Y chromosome.  He clearly had many willing and unwilling sexual partners.  However any woman’s genes attached to his will have prospered (particularly down the male line), even if the woman herself didn’t.  This is a good example of  a woman having different interests to men (she wants commitment and the man doesn’t).  It is also an example of a woman having different interests to her own genes – it is in her genes’ interest for her to be attracted to unreliable, philandering men, perhaps by convincing her that she will be the only one who will tame him and make him exclusively her’s!  The old adage seems to ring true – women marry men expecting them to change, and they don’t.  Men marry women expecting them not to change, and they do.

We have good evidence that men will generally find a woman less attractive if they find out she is in a sexual relationship with another man.  Women generally find men more attractive if they are attached (and therefore presumably attractive) to another woman.  Her genes will recognise that he may be a good bet in propagating themselves into the next generation because if one women finds him attractive then others might too. These characteristics are in the mother’s genes’ interests if they have a son together and the son inherits his father’s characteristics.  Again this behaviour is very much in the genes’ interests but may be against the interests of their host (the woman) .

This also may explain why many cultures favour sons over daughters.  No cultures favour daughters.  Sons are a much better way of getting lots of your genes into future generations than daughters – whether you are a man or a woman.

An interesting question:  would a mother object to a highly promiscuous son?  He would be a route to having more of her genes propagated into future generations.

Nothing here should make us believe we can predict the behaviour of individual men and women.  Also, I’m describing the is not the ought of human behaviour.  The ought of human behaviour cannot and should not be decided (or justified) by evolution.  Morals, ethics, civilised evidence based debate and the rule of law are the only mechanisms for reaching a consensus of how we as individuals ought to behave.  Evolution is about survival of our genes and does not care one jot about human happiness, fairness or equality.

Genetic Explanations

Why Poorer Students Are Underrepresented In Top Universities – an Evolutionary Perspective



“Top” universities are under pressure to recruit poor students with lower grades and to do more to recruit more pupils from “poorer” backgrounds.

7% of children go to private schools and make up a much bigger proportion of top university places.  Intuitive logic leads us to believe that it must be the private schools that make the difference. So something must be done to level the playing field for equally talented poorer children.

However, there is little hard evidence that proves conclusively that good quality private schools give an unfair advantage.  So recently the UK Government’s university funding body did some research on 132,000 students to try to prove this “causal link” between good quality schools and academic success.   If this link was proven they could demand that pupils from poorer schools should be given lower grades to enter the top universities on the assumption that it would take higher levels of intelligence to get the same grades as pupils at better schools.  Surprisingly for many, the study showed the effect of the quality of schooling was much smaller than was imagined.  Astoundingly, for the very brightest pupils the quality of schooling made no difference at all to their ultimate academic success.

So this intuitive “conclusion” that affluent children attending good schools have an unfair advantage over equally talented children at poorer schools is not supported by the facts.

The expected “causal link” between academic success and private schools failed to take into account three massive confounding factors:

1. Personality and intelligence is largely genetically inherited from our parents.

2. We do not mate randomly.  i.e. we carefully choose our sexual partners.  This is a phenomenon called “assortative mating”.

3. We now have adequate social mobility so bright children eventually find their due place in society before they have children.

So how do these factors affect society? It perfectly explains these facts:

Let’s start by looking at a few seemingly unrelated facts:

1. The research highlighted in The Times on 17th June 2013 shows that the 24 largest research universities in the Russell Group admit a lower proportion of undergraduates from state schools and from poor families than ten years ago.

2. Children from wealthier families were nearly twice as likely to leave school with five good GCSEs, including maths and English, as those from poorer families — 63% against 36%.

3. After the ludicrously embedded class system in UK was largely dismantled after the last war we saw a massive surge in social mobility, which has now come to a screeching halt.

4. It seems poor white children do worse than poor ethnic minorities despite having a similar “poor” upbringing and environment. i.e. poorer outcome, same nurture.

5. Of the 20 top local authorities in terms of sending pupils to the prestigious Russell Group universities, 19 are in London and the south. Of the 20 worst-performing councils on the same league table, 18 are in the north.

Overwhelming evidence from identical twin studies, adoption studies, molecular genetics and Mendelian genetics give us a big clue. But it is difficult to piece all the strands together causing billions of tax pounds to be wasted on closing a “perceived” gap in equality.

First we must acknowledge that talent and motivation are largely heritable (i.e. we receive them through our genes).  The massive data from identical twin / adoption studies have shown that the “environment” of pupils before World War 2 accounted for some of the differences in a person’s eventual social status by age 35. For example, an intelligent working class child born into a 1920s Welsh coal mining community had little chance of getting to university.

After World War Two there was an enormous amount of social mobility due to Grammar Schools, public school scholarship and much improved State schools.  As the social restrictions in our society were removed children with the genes that coded for talent and motivation broke free.  This happened across Britain with working class children shooting up the social scale with talent in science, engineering, law, sports and the arts.

These talented people did well.  They earned a good living, achieved a higher social status and joined the affluent middle classes.  Combine the fact that talent and motivation is largely inherited through our genes 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. Also these talented genes will move and cluster to where the best jobs are.  i.e. in London and the South East of England.

This is unfair, but I’m explaining the is not the ought. This biological process is called “assortative mating”.   As these (now middle class) children had parents who were more affluent they also had a higher chance of being sent to a private school.

So effectively, genes for talent and motivation starting leaving the working class areas (such as coal mining villages) after World War Two and became middle class. 

We would predict that eventually we would see a more polarised genetic society as the genes for talent and motivation are slowly leached out of the working class areas.  Eventually social mobility will slow down and humanities educated journalists and politicians will scratch their heads and wonder why, and then conclude that more must be done to help the talented working class children who used to exist but have now mysteriously disappeared.

Genetic studies since World War 2 (in the developed world) shows upbringing makes little difference to our eventual social status, peer groups makes some difference but the largest driver is the genes for talent and motivation we inherit from our parents.  Our upbringing, education and experiences are transient, so the  influence of different “nurture” experience on our lives will be diminished over time.  Our genes exert their influence consistently throughout our whole life.

This explains what we have seen in recent history. A strong genetic determinant of talent and motivation combined with a sudden dismantling of unfairness in society will lead to an initial surge in social mobility. However this social mobility will then fade as beneficial genes cluster into the affluent parts of society by the process of assortative mating.

The top private schools are highly selective and have rigorous academic entry requirements.  This alone would explain why private schools have a disproportionate number of students at top universities.  Assortative mating further explains why private schools and affluent families provide a disproportionate number of students to top universities on merit, and why they are providing slightly more now than 10 years ago.  As assortative mating continues its influence this trend is likely to continue, unless our politicians want to start choosing with whom we mate?

Top universities may be becoming less socially representative, but they are representing where the talent has clustered because in a relatively socially mobile environment, talented genes will cluster in affluent parts of society.

For new immigrants the social factors which have limited their progress until now are relatively recent, so we expect the genes for talent and motivation to be more numerous in poorer parts of their society as they haven’t had time to cluster in the more affluent parts of society.

This explains why poorer students from ethnic minorities out-perform their white peers. i.e. same nurture but better outcome.

As the better paid jobs in the UK are predominantly in London we could also predict that there would eventually be a migration of talented genes from other parts of the UK to the south-east of England causing an academic north-south divide. This also seems to be the case (reference and explanation).

Remember is not ought.

The breathtaking irony is that social mobility has stopped because society is more equal. Social mobility has allowed genes that denote talent and motivation to cluster in affluent parts of society by the process assortative mating.

The class-war warriors and socialists had a laudable dream of equality whereby poor working class children would be fairly and equally represented in society.  They made the assumption that talented and motivated children were thrown up by society at random.  i.e. that talented and motivated children are equally spread across class and relative affluence.  So once “equality” was achieved they imagined a world where there would be a fair representation of working class originated talent in the top echelons of society in perpetuity.

They were wrong. Society is now much more equal, but because talent and motivation are largely genetically encoded the talent has just migrated to the affluent parts of society by the process of assortative mating.

Or put another way, intelligent and motivated individuals tend to increase their social and economic status in a relatively socially mobile society. It’s not the posh getting cleverer, but the clever getting posher.

Our future is not entirely genetically determined and I have no doubt that good schools with quality teachers make a difference.  We should continue do everything we can to ensure that individuals from all parts of society have access to an excellent education and quality careers with equal opportunity to succeed on merit alone.  But if we are to have a serious debate on helping “disadvantaged” children we need to look at all causes of inequality and move away from the discredited 1960’s assumptions that it is explained by “nurture” and “class”, which is what most press articles on the subject imply. We should learn a little about evolutionary biology and genetics before making these wild assumptions.

It is in our interest as a society that we have the best people in the right jobs. We all benefit from a genuine meritocracy.  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 of a perceived injustice unless we can prove beyond doubt that they really have been disadvantaged.

Governments should set their expectations correctly before spending billions more tax pounds trying to save all pupils from a “perceived” injustice. They should instead target Government spending on developing each child’s individual and innate talents and motivations.

Further listening on the genetics of intelligence:

Intelligence: Born Smart, Born Equal, Born DifferentThree BBC Radio programmes 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.


Pleiotropy across academic subjects at the end of compulsory education An article in Nature on the genetic effects to human intelligence and GCSE results in the UK.

Differences in degree outcomes: Key findings  (examines the extent to which a student’s background affects their chance of obtaining an upper second or first class degree)

Twins early development studies

Differences in students’ GCSE results owe more to genetics than environment:

IQ is in the Genes

We can’t ignore the evidence: genes affect social mobility

One Cause of Inequality: More Rich Marrying One Another

Marry Your Like: Assortative Mating and Income Inequality

Women, Men and the New Economics of Marriage

Why is there an academic north-south divide in Britain?

How Much Difference Does a Good School Make to Your Child’s Academic Achievement?

Getting ’em young (The Economist looks at the impact of early years education)

Genetic influence on GCSE results

Genetics and general cognitive ability : Article : Nature

Genetics – How Intelligence Changes with Age

Access : Childhood intelligence is heritable, highly polygenic and associated with FNBP1L 

Genes may play role in educational achievement

Access : Genome-wide association studies establish that human intelligence is highly heritable and polygenic 

Genetic and environmental contributions to the covariance between occupational status, educational attainment, and IQ