From an evolutionary perspective, if we see a genetic opportunity, one that offers us the prospect of improving our genetic standing, then we will feel obliged to take it. After all, the making of such advances is our very purpose of being.

There is therefore a genetic argument to suggest that inbreeding may be beneficial given that it has the potential to further an individual’s genes – the more an individual can spread their genes, the better their genetic prospects.

Certainly for the male, given that they have females in attendance over which they are physically stronger, inbreeding offers easy sexual and reproductive pickings. Inbreeding would be a way to extend a male’s genetic presence without them having to put in too much effort.

It’s a quantity-versus-quality argument. The more mud that is thrown, the more likely it is that some will stick. The more of their genes that they put out there, the more likely they are to secure their genetic future.

And yet, inbreeding – reproducing with first-degree relatives – is not a normal behaviour within humanity.

Various reasons have been suggested as to why this might be the case:

• Civilisation has made incestuous relationships taboo. Many societies outlaw the practice. Nevertheless, this is an unlikely reason as to why inbreeding is so rare. Most animal species also avoid inbreeding. Therefore, there can be no definitive link between it and living in a civilised society. There is no reason to believe that our enhanced communal relations have made us more sexually sophisticated.
• Our greater cognitive awareness has made us more aware of the dangers and complications of inbreeding. We may, for instance, recognise that inbreeding increases the incidence of genetic disorders, which is why we tend to avoid it. But, again, other species – even those of limited intelligence – avoid inbreeding. It is certainly not a behavioural trait acquired through our greater mental abilities.
• We may recognise that inbreeding is a poor genetic investment. Although inbreeding offers us the opportunity to extend our genes, it does not necessarily maximise our genetic potential. There will be other more attractive prospects. There will be better opportunities elsewhere. Inbreeding is not considered a favourable reproductive strategy because it does not take advantage of the benefits that might be gained from a species’ genetic variation. The problem is that this idea does not adequately address the easy-pickings argument. For males at least, the cost of inbreeding would be minimal. There’s not a lot to lose from it. So, even if there were better opportunities, they could decide to bank an incestuous relationship as a fallback. There’s no reason why males cannot have the best of both worlds, reproducing with close relatives and with others that offer more genetic variation.

The inability to point to any clear reason why inbreeding is shunned has led some to assert that there may be a built-in genetic defence mechanism – a gene that precludes us from being attracted to our closest relations.

Given how rare inbreeding is across Nature, the suggestion is that most species carry this gene. It exists to prevent the damaging consequences of inbreeding.

The evidence, however, suggests that such a gene does not exist. And there’s a reason for that; such a gene is just not needed.

Nature excels at being efficient. Everything has a purpose; everything has to justify its existence. Wastefulness is not tolerated. If we needed a gene to prevent inbreeding, then we would have acquired one. We just don’t need one.

This is because we, as do all species, have a level of self-awareness. We know what we can do and what we can’t do; we know what we’re good at and what we’re not so good at; we know what we’d like to be better at and what we’re not concerned about.

This self-awareness is most developed in humanity, but it also appears throughout the animal kingdom. A stalking predator knows how close it must be to its prey before it can launch an attack; an animal that relies on camouflage for survival knows where to position itself to blend into the background.

As individuals, we know our strengths but, perhaps more importantly from an evolutionary point of view, we also know our faults and failings. We can be very self-critical. It’s not so much that we don’t like ourselves (though some individuals will hold that view), but that we will not be entirely satisfied with ourselves.

“If only I could do this; if only I were better at that.”

We will want to improve on ourselves. We will want to be better at doing what we need to do. Ultimately, that is how we will ensure our genetic survival.

We will also know that if we have issues or weaknesses, then so does our family. That’s because they’re part of the same genetic order. We are of their making. That means that if we want to overcome or avoid certain challenges, we have to get away from them. Only by bringing in other, non-related genes can we seek to improve on our condition.

This is the case even if we “look up to” our older brothers or revere our father. We still recognise that we have failings, that those failings are a part of both them and us. They can only give us more of what we already have. As much as we may love our family, we will want more than they can offer. We will want something that they cannot give us.

This is why we look for a reproductive partner who adds genetic value. They may have some of the qualities that exist within our family, but they will also offer us something more.

To have a gene that inhibits inbreeding would be a substantial, unnecessary genetic investment. It’s far more efficient to proscribe this behaviour through other means. Self-awareness is the tool that achieves this.

Different species have then developed mechanisms to facilitate genetic improvement by ensuring they reproduce with a non-related partner.

• Negative imprinting – A close association between siblings during childhood reduces sexual attraction between them later in life.
• Dispersal – In many species, as individuals reach sexual maturity, they move away from the rest of the family unit. This encourages them to reproduce with non-related individuals and leads to a better mixing of the genetic population.
• Sensory factors – Some species use scents to help them identify related individuals. This stops them from reproducing with their own kin.
• The female’s role as genetic gatekeeper. With their biological form, females are aware of the commitment and investment involved in reproduction. They also realise they have only limited reproductive opportunities. They are therefore particularly keen to ensure that they only reproduce with the best male product, the one that will maximise their genetic returns. This could be their father, brother or son. In practice, because of a critical self-awareness, it tends not to be.
• Humanity has used its societal development as a tool to demonise incestuous relationships, making them unacceptable, undesirable, unpalatable. Avoidance of incestuous relationships has become an ingrained, normal behaviour.

Just as we don’t need a gene to stop us from reproducing with other species, we don’t need a gene to stop us from inbreeding. It’s just not an attractive proposition. There’s little to be gained from it, especially when compared with the possibilities that might arise from pursuing non-related prospects.

Individuals want genetic enhancement. They can only acquire it by taking advantage of the genetic variation available. Nature, by providing a level of self-awareness, has given us our motivational drive. It obliges us to act in the best interests of our genes.

It’s a very rational, efficient approach, but then, that’s Nature, so methodical and so purposeful.

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