The way we think about genes presents one of the biggest obstacles to understanding evolution and its relevance in the modern world. For natural selection to change a trait, there need to be genetic differences in that trait among individuals. And if that genetic variation leads to differences in reproductive success, then evolution is happening.
An avalanche of data shows that genetic differences affect almost any trait you care to measure, from obesity risk to intelligence. The proportion of variation that is due to genetic differences is called the heritability of the trait. But where does all that heritable variation come from?
In biology class and in the media we hear about genes “for” various traits: eye colour springs immediately to mind. As if there were a tiny piece of DNA lurking in our genome, existing only to imbue our iris with the perfect hue.
There are diseases to be cured and money to be made from identifying single genes with big effects. But most genes affect many traits, and nearly all traits arise from the action of hundreds or even thousands of genes. This means it makes little sense to think of most genes only in terms of their effect on one particular trait.
It also means that just about any measurable trait that differs among individuals will be subject to genetic differences. This point has just been spectacularly illustrated by a study of mobile phone use - a behaviour barely one generation old.
A new twin study estimates that 34 to 60 percent of variation in mobile phone use among Australian teenagers is due to genetic differences.
University of New Mexico evolutionary psychologist Geoffrey Miller and collaborators from the Queensland Institute for Medical Research asked pairs of teenage twins about how often they call and text, as well as measuring their performance on personality and intelligence tests. They then statistically dissected how much of the overall variation in these measures was due to genetic differences, shared family environment and other sources of variation.
Intriguingly, not only was much of the variability in phone use due to genetic differences, there were also genetic associations between phoning and both intelligence and extroversion. The genes that dispose some kids to being more extroverted than others also dispose them to using their phones more. And the genes that raised some kids’ intelligence also reduced their telephoning habits.
Miller is a pioneering of the evolutionary study of consumer behaviour. His 2009 book Spent: Sex, Evolution and Consumer Behaviour takes an entertainingly bemused look at the evolved motivations behind the crazy things we buy. His research explores what happens when a genome that evolved in a history of hunting, gathering and subsistence farming and crashes into a post-industrial consumer economy.
He told the Sydney Morning Herald:
One of the big misconceptions that almost everybody has is that you can only have genes for things that evolved in the past…That was one of the things we wanted to demonstrate in an in-your-face way: that even with a technology that’s only been around for a couple of decades, you can still have these latent genetic influences that will shape people’s personality traits, their interests, their styles of social interaction.
Genetic variation in mobile phone use illustrates one of the surprising ways in which our evolved genome shapes our modern behaviour. It also obliterates the too-common idea that cultural innovation shields humans from all forms of natural selection.
While it might be drawing a long bow to predict strong evolutionary selection on mobile phone use, genetic differences in the tendency to adopt and use other technologies in our distant past almost certainly altered the course of our evolutionary history. Several times over.