People increasingly use social media platforms like Facebook and Twitter as their primary source for news and information. Studying social media habits, therefore, can offer rich insight into the political opinions of a nation. Brazilian researchers mapped the online behavior of 12 million Facebook users in Brazil in 2013, 2014 and 2016. What emerged was a stunning visual picture of an ever more polarized country. Then, in 2017, they mapped clicks in the US and Argentina, too, with predictably alarming results: both countries have split into two sides, right and left, that share almost no common ground. Pablo Ortellado and Márcio Moretto Ribeiro explain.

Hundreds of plaintiffs are suing Monsanto, contending that exposure to glyphosate – the active ingredient in its Roundup weedkiller – gave them cancer. The World Health Organization calls glyphosate a probable human carcinogen, but the U.S. Environmental Protection Agency says that used properly, it does not threaten human health. Epidemiologist Richard G. “Bugs” Stevens of the University of Connecticut explains why proving causation in medicine is much like proving it in a jury trial – and why it’s not easy in either setting.