I’ve been thinking about genetics and causation. It’s my job (genetic counsellor) to explain genetics to people and to do this I use lots of metaphors. Here’s a rather extended one I came up with in the pub. You won’t be surprised to know, it involves booze.
The aim of the metaphor is to challenge the rhetoric of “genes for X” or a “X gene.” It’s makes little sense to talk of “genes for intelligence” or “gay genes” for example. I below I hope to make it clear why not:
Imagine there are two aliens who have come to investigate humans behaviour. They’re sitting up on their space ship observing a typical British town on an average Saturday night. While observing they see some pretty strange things. These aliens are curious so they want to find out what causes people to behave how they do.
Now these two aliens are quite clever so they set about observing. They notice there appears to be a common factor in the causation of these strange behaviours. It appears, although they’re not quite sure how, it involves the imbibing of a drink called alcohol. The Aliens notice that there are different types of alcoholic beverages and, in some way, these affected how humans behave.
The first of the Aliens, called Zorg-The-Magnificent, decides to investigate. He puts on his cloak of invisibility and wanders into a bar in a town called London. Now being an average London bar the music is playing so loudly that no one can hear each other talk. This does not matter as the humans have overcome this problem by having a handy menu by which customers can order their drink. The menu, usefully, has a neat set of instructions for how to make the drink. Zorg observes a customer point to the drink on the menu. Written is:
Vodka Red Bull: Mix 2 shots of finest vodka* with one can of red bull
*For best results, vodka should be of the sort that can strip paint at forty yards.
Zorg notices a strange change in behaviour of the gentleman who imbibed the drink. Instead of wondering around politely pretending he can hear what other people are shouting over the music, the gentleman now wonders from situation to situation like a hyperactive squirrel with ADHD. Occasionally the gentleman stops to swat some imaginary flies at high pace. Later Zorg finds out this called dancing.
Zorg takes his findings back to his friend, the other alien adventurer, named Jeff.
“Jeff!” Says Zorg-The-Magnificent, excitedly “I’ve found a startling discovering, I’ve found the drink for wondering about like an overexcited squirrel and dancing like you’re trying to squat flies as if you’re life depends on it. What’s more,” continues Zorg “I’ve found the very thing that makes it all possible.” At this point Zorg triumphantly produces a menu that he had purloined from the bar.
“There” He says pointing to the description of Vodka Red Bull “there’s your ‘drink for squirrel attention span and idiotic dancing’”
Now Jeff is a bit more of a skeptical alien and is not quite convinced by the theory. He wants more proof and would like to repeat the observation. So Jeff decides to visit a pub for himself.
So Jeff dons a cunning disguise to walk among us and locates a pub. It’s a pub that’s quiet and populated by locals who like it quiet. Jeff wanders in, takes a seat, and begins his observations.
This pub it not one designed to maximise social discourse. In fact it’s precisely the opposite. It’s been designed to allow people of a certain age to mingle in each other’s company with the least amount of conversation possible. Consequently they have designed a cunning system for ordering drinks with the minimum of fuss. Just as in the bar with loud music, this pub has a menu, again with a small description of how to make the drink.
Jeff looks around. Not one person has ordered a ‘Vodka Red Bull’. Perhaps they just need a bit of time, he thinks. An hour passes and no one orders a Vodka Red Bull, so Jeff decides he needs to hurry things up. Subtly he pulls out his mind ray gun and zings the nearest punter. The man he zings walks to the bar and points to a Vodka Red Bull. The barman kindly obliges, and Jeff sits back waiting for a frenzied squirrel impression and manic dancing. But nothing happens. The punter who orders the drink is perhaps brooding with a little more verve, but nothing like the behaviour that Zorg had observed.
Jeff then looks at what the other people are drinking. A lady walks to the bar, “Gin please” she says, pointing to the list where the instructions simply say. “Pour gin.” Jeff observes as the gin, almost instantly, causes the women to weep at an emotional episode of Deal or No Deal playing silently on the pub’s TV.
“Well now!” Says Jeff when he returns to the alien space ship. “I’ve disproved your ‘Vodka Red Bull’ theory but never fear, I’ve found the drink for weeping uncontrollably at silly things! Here!” Jeff produces the simple instruction “Pour Gin” and shows it to Zorg.
A robust debate ensues between Zorg the Magnificent and Jeff regarding the relative merits to their two theories. Zorg is convinced by his ‘Vodka Red Bull’ theory however Jeff thinks this is baloney, and wishes to pursue his ‘Gin makes you weepy and silly things’ hypothesis.
They decided the only way to settle the debate is to gather more information. They decide to go out into more bars, find more menus and observe more behaviour.
This is what they do, returning to their spaceship only after many months of research. The conclusion they reach is that the relationship between drinks menu and type of human behaviour is extremely complicated. Some drinks can increase the chance of certain strange behaviours, but behaviour is also determined by the venue, and in some places no matter how much Vodka Red Bull is consumed it will never bring the manic dancing observed in the bar with loud music.
Additionally, sometimes the drinks were ordered wrong. In one bar, for example, Jeff observed a young man ordering a ‘Vodka Red Bull’ only to be misunderstood and given a completely different drink. Later Zorg observed the man believing he could sing like Elvis Presley.
At one point Zorg and Jeff became very exited when they thought they had discovered the drink menu choice for phoning your ex and leaving an embarrassing message. This rather marvellous cocktail however was hard to make and was often misspelled on menus, so the instructions weren’t always followed exactly. Therefore, in the grand scheme of things, the cocktail only turned out to only be one of many (minor) causes of phoning your ex and leaving an embarrassing message.
The time came for Zorg and Jeff to return home. They looked at their findings, pleased with what they had discovered. They had collated a wide range of bizarre human behaviours that happened on Saturday nights due to alcohol consumption. They had their menus, with the different drinks explained on them, with a nice theory of how, in the right conditions, they could lead to the multitude of strange human behaviour.
Genes, in this analogy, are the drink menus. They ‘code’ for the physical substances that play a part in bringing about a human trait. In the same way you can’t have a drink menu option for dancing like a pillock, you can’t have a ‘gene for’ most human traits. Instead you have genes that code for substances that make something more likely.
Importantly, the causal chain (drink description > making drink > drinking drink > dancing like a pillock) is complicated. Whether or not the drink brings about a specific effect depends on where and how it’s made, and with whom it is drunk. In the same way the causal chain from genes to trait is complicated. The physical and cultural environment in which genes are expressed plays a huge part what human trait eventually comes about. A gene might make something more likely to happen, but only in certain circumstances.
So next time you read an article saying there is a ‘fat gene’ or ‘gene for intelligence’ stop and congratulate yourself, smugly thinking to yourself. “ I think you’ll find it’s a bit more complicated then that. I know, Zorg and Jeff taught me how.”