In 1665, a bundle of cloth from London arrived at the door of the tailor for the village of Eyam, a tiny community in the midlands of England. Within a week, the tailor’s assistant was dead.
The cloth contained fleas that carried the bubonic plague, and it didn’t take long for the disease to spread throughout the village. But the destructiveness of the disease is less impressive than the valor of its victims: the villagers voluntarily quarantined themselves to prevent the plague from spreading into the surrounding countryside. In little over a year, all but 83 of Eyam’s 350 or so residents were dead. But the infection had been contained.
The Eyam case has been heralded as a rare example of astonishing self-sacrifice. But some scientists believe that each of us does something similar, however unintentionally, when we are ill. According to the “Eyam hypothesis,” sickness behaviors — the set of coordinated behavioral changes, such as depression, lethargy and loss of appetite, that help the body cope with illness and injury — might have evolved in part because they make us more reclusive, thereby preventing us from spreading our disease. By refusing food, sleeping all the time and avoiding others, we could be saving our friends and family from our fate.
This hypothesis hasn’t been proven experimentally. But it just got a boost thanks to some rather selfless mice.
In a study published on Monday in the journal Scientific Reports, biologist Patricia Lopes describes how wild mice living in an abandoned barn in Switzerland began to avoid their social groups when they felt ill. When she and her colleagues modeled the effects of this behavior change, they found that it dramatically slowed down the spread of disease.
“We don’t know why the mice are doing this,” Lopes said, “but as a consequence of the sick mouse changing its behavior and moving away from the nest, its relatives would have a better chance of not getting the disease and surviving, and they would pass on genes that are common to the sick mouse. … That could make the behavior evolutionarily advantageous.”
The individual advantages of sickness behavior are well known. Lack of hunger means that animals don’t need to waste energy and expose themselves to attack by foraging for food. Overall lethargy means the body’s energy can be directed entirely toward maintaining a fever — the most metabolically taxing part of the immune response. But the benefits of some aspects of response are less clear.
It’s important to note that the mice aren’t quarantining themselves consciously as the people in Eyam did. And the idea that an evolutionary mechanism might be behind this behavior still needs to be proven experimentally.