Although several studies have looked at the spread of animal behaviour in captivity, it has been difficult to do the same in wild populations. Given great tits’ reputation for innovation, zoologist Lucy Aplin and her colleagues set out to see how these ideas propagated. First they needed a new innovation. The team headed out into Wytham Woods, near Oxford, and set up a puzzle box containing mealworms. If the birds wanted to get the food inside, they’d need to move a sliding door in a certain direction. To see how the birds interacted, the researchers tagged almost all the tits in the area with automated tracking devices. ‘We could get real-time information about how and when individuals acquired knowledge,’ Aplin said. ‘The automated data-collection also meant we could let the process run without disturbance.’[32]
The birds grouped together into several different sub-populations; in five of these populations, the researchers taught a couple of birds how to solve the puzzle. The technique spread quickly: within twenty days, three in every four birds had picked up the idea. The team also studied a control group of birds, which hadn’t been trained. A few eventually worked out how to get into the box, but it took much longer for the idea to emerge and spread.
In the trained populations, the idea was also highly resilient. Many of the birds died from one season to the next, but the knowledge didn’t. ‘The behaviour re-emerged very quickly each winter,’ Aplin said, ‘even if there were only a small number of individuals that were alive from the previous year and had knowledge of the behaviour.’ She also noticed that transmission of information between birds had some familiar features. ‘Some general principles are similar to how disease spreads through populations, for instance more social individuals being more likely to encounter and adopt new behaviours, and socially central individuals can act as “keystones” or “super-spreaders” in the diffusion of information.’
The study also demonstrated that social norms could emerge in wild animals. There were actually a couple of ways to get into the puzzle box, but it was the solution the researchers had introduced that became the accepted method. Such conformity is even more common when we look at humans. ‘We’re social learning specialists,’ Aplin said. ‘The social learning and culture we observe in human societies is of a magnitude greater than anything we observe in the rest of the animal kingdom.’
We often share characteristics with people we know, from health and lifestyle choices to politicial views and wealth. In general, there are three possible explanations for such similarities. One is social contagion: perhaps you behave in a certain way because your friends have influenced you over time. Alternatively, it may be the other way around: you may have chosen to become friends because you already shared certain characteristics. This is known as ‘homophily’, the idea that ‘birds of a feather flock together’. Of course, your behaviour might be nothing to do with social connections at all. You may just happen to share the same environment, which influences your behaviour. Sociologist Max Weber used the example of a crowd of people opening umbrellas when it starts to rain. They aren’t necessarily reacting to each other; they’re reacting to the clouds above.[33]
It can be tough to work out which of the three explanations – social contagion, homophily or a shared environment – is the correct one. Do you like a certain activity because your friend does, or are you friends because you both like that activity? Did you skip your running session because your friend did, or did you both abandon the idea because it was raining? Sociologists call it ‘the reflection problem’, because one explanation can mirror another.[34] Our friendships and behaviour will often be correlated, but it can be very difficult to show that contagion is responsible.
What we need is a way to separate social contagion from the other possible explanations. The most definitive way to do this would be to spark an outbreak and watch what happens. This would mean introducing a specific behaviour, like Aplin and her colleagues did with birds, and measuring how it spreads. Ideally we would compare results with a randomly selected ‘control’ group of individuals – who aren’t exposed to the spark – to see how much effect the outbreak has. This type of experiment is common in medicine, where it’s known as a ‘randomised controlled trial’.
How might such an approach work in humans? Say we wanted to run an experiment to study the spread of cigarette smoking between friends. One option would be to introduce the behaviour we’re interested in: pick some people at random, get them to take up smoking, and then see whether the behaviour spreads through their friendship groups. Although this experiment might tell us whether social contagion occurs, it doesn’t take much to spot that there are some big ethical problems with this approach. We can’t ask people to adopt a harmful activity like smoking on the off chance it will help us understand social behaviour.
Rather than randomly introducing smoking, we could instead look at how existing smoking behaviour spreads through new social connections. But this would mean rearranging people’s friendships and locations at random and tracking whether people adopt their new friends’ behaviour. Again, this is generally not feasible: who wants to reshuffle their entire friendship network for a research project?
When it comes to designing social experiments, Aplin’s work on birds had some big advantages over studies of humans. Whereas humans may keep similar social links
