Read the full article at the New York Times.

Hours after the Las Vegas massacre, Travis McKinney’s Facebook feed was hit with a scattershot of conspiracy theories. The police were lying. There were multiple shooters in the hotel, not just one. The sheriff was covering for casino owners to preserve their business.

The political rumors sprouted soon after, like digital weeds. The killer was anti-Trump, an “antifa” activist, said some; others made the opposite claim, that he was an alt-right terrorist. The two unsupported narratives ran into the usual stream of chatter, news and selfies.

“This stuff was coming in from all over my network of 300 to 400” friends and followers, said Mr. McKinney, 52, of Suffolk, Va., and some posts were from his inner circle.

But he knew there was only one shooter; a handgun instructor and defense contractor, he had been listening to the police scanner in Las Vegas with an app. “I jumped online and tried to counter some of this nonsense,” he said.

Skepticism of online “news” serves as a decent filter much of the time, but our innate biases allow it to be bypassed, researchers have found — especially when presented with the right kind of algorithmically selected “meme.”

At a time when political misinformation is in ready supply, and in demand, “Facebook, Google, and Twitter function as a distribution mechanism, a platform for circulating false information and helping find receptive audiences,” said Brendan Nyhan, a professor of government at Dartmouth College (and occasional contributor to The Times’s Upshot column).

For starters, said Colleen Seifert, a professor of psychology at the University of Michigan, “People have a benevolent view of Facebook, for instance, as a curator, but in fact it does have a motive of its own. What it’s actually doing is keeping your eyes on the site. It’s curating news and information that will keep you watching.”

That kind of curating acts as a fertile host for falsehoods by simultaneously engaging two predigital social-science standbys: the urban myth as “meme,” or viral idea; and individual biases, the automatic, subconscious presumptions that color belief.