In the mid-1800s a caterpillar, the size ofa human finger, began spreading across the northeastern U.S. This appearance ofthe tomato hornworm was followed by terrifying reports of fatal poisonings andaggressive behavior towards people. In July 1869 newspapers across the regionposted warnings about the insect, reporting that a girl had died after a run-inwith the creature. That fall a local newspaper printed an account from adoctor. The physician warned that the caterpillar was “as poisonous as arattlesnake” and said he knew of three deaths linked to its venom.
Although the hornworm is a voracious eaterthat can strip a tomato plant in a matter of days, it is, in fact, harmless tohumans. Entomologists had known the insect to be innocuous for decades, and hisclaims were widely mocked by experts. So why did the rumors persist even thoughthe truth was readily available? People are social learners. We develop most ofour beliefs from the testimony of trusted others such as our teachers, parentsand friends. This social transmission of knowledge is at the heart of cultureand science. But as the tomato hornworm story shows us, our ability has agaping vulnerability: sometimes the ideas we spread are wrong.
Over the past five years the ways in whichthe social transmission of knowledge can fail us have come into sharp falls.Misinformation shared on social media has fueled an epidemic of false belief.The same basic mechanisms that spread fear about the tomato hornworm have nowintensified – and, in some cases, led to – a profound public mistrust of basicsocietal institution.
“Misinformation” may seem like a misnomerhere. After all, many of today’s most damaging false beliefs are initiallydriven by acts of disinformation, which are deliberately deceptive and intendedto cause harm. But part of what makes disinformation so effective in an age ofsocial media is the fact that people who are exposed to it share it widelyamong friends and peers who trust them, with no intention of misleading anyone.Social media transforms disinformation into misinformation.
Many social scientists have tried tounderstand how false beliefs persist by modeling the spread of ideas as acontagion. In a contagion model, ideas are like viruses that go from mind tomind. You start with a network, which consists of nodes, representingindividuals, and edges, which represent social connections. You seed an idea inone “mind” and see how it spreads.