News of disease outbreaks can warp our brains in strange and subtle ways

The "behavioural immune system" can drive harsher moral judgement and may even contribute to xenophobia.

Disease and death are back in the headlines. The Ebola outbreak in the Democratic Republic of Congo is currently outpacing response efforts, and concerns about hantavirus linger, as new patients test positive for the infection. 

Most of us will never come into contact with these pathogens, and so we should have no need to protect ourselves from the infections – but the news stories about them may nevertheless be influencing our minds in surprising ways.

As I first described for the BBC in April 2020, we are hardwired with a "behavioural immune system" that can shape our psychology at the merest suggestion of illness. Reminders of infection can lead us to become more conformist and risk-averse, less open-minded towards those who break social norms. There are even signs that it can contribute to xenophobia.

A prehistoric protection from infection

The body's immune system includes some incredible weapons to strike infection once a pathogen enters our bodies – from the macrophages that engulf pathogens to the B-cells and T-cells that create specialised antibodies that can provide us with later immunity. Activating this army requires a huge amount of our energy, however – leaving us depleted at the end of the illness.

We have therefore evolved a set of psychological responses – named the behavioural immune system by Mark Schaller at the University of British Columbia – that should reduce our contact with pathogens in the first place.

Its most basic mechanism is disgust; we naturally avoid anything that looks or smells like it might put us at risk of infection. It's the reason we retch when we smell rotting food.

Alongside this visceral response, the behavioural immune system involves subtler mechanisms that ensure we follow social norms. This would have been important, since cultures would have typically evolved certain rules – such as the hygienic preparation of food, or the disposal of waste – to reduce the spread of diseases that were common in their area. And in times of an outbreak, it would have been especially important that people stick to those protocols.

As a result, reminders of illness can make us more conformist.

That's the theory, at least – and a host of studies lend some support to the idea. In one experiment, Schaller asked participating students to vote on a proposed change to the school's grading system. He found that they were far more likely to vote in line with other students' opinions – a sign of conformity – if they had just recalled a time when they had been........

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