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


4 thoughts on “Why homosexuality is natural – an evolutionary explanation

  1. John says:

    What do you think of Gegory Cochran’s explanation that homosexuality is the byproduct of a (likely transient) childhood infection, and that the “genetic component” of homosexuality is merely a predisposition? Given that the heritability of homosexuality (in males) is rather low (~35%), and the concordance rate for MZ twins is even lower (~25%), combined with the fact that homosexuality is much rarer (or even absent) in most hunter-gatherer populations, so rare that, in many cases, they lack even a rudimentary concept of it – you have to explain to them what you mean when you bring it up.

  2. Wayward says:

    It’s funny but I came to the same conclusions based upon the same evolution reasons. But, there is one additional idea that solidified things. Is it a choice or is it in their genes that men are attracted to women? ie. If we put about 50 male and female babies on an island and left them alone, would the males and females eventually become attracted to each other? I think that’s a yes. If so, we should expect a male homosexual to be also attracted to a women. But, that’s not the case. As a result, there is a strong argument that something has cross-switched genetically. The homosexual male should be stimulated by certain genetic cues but is not. This scenario is the reason that makes me strongly believe that homosexuality is not a choice but genetic.

  3. hydeouscreature says:

    There are so many factors contributing to homosexuality; no offence meant, but this might be just scraping the tip of the iceberg; if I were to go with what the social sciences have to say about it, there’s no way that homosexuality dwindling over the years to come, :).

  4. Pingback: Gay Marriage and Liberty | RGAmbler

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