A new PNAS paper finds that polarization increased immediately after the invention of smartphones and the advent of social media, which both appeared around the same year, 2008. Both profoundly changed the way humans communicate and this rise of connectivity may have fueled polarization. Adding a small number of individuals with extreme opinions (influencers) also drives continuous increases in polarization. Once polarization occurs as a consequence of increasing connectivity, it can not simply be undone by reversing to previous connectivity levels. This may be why social media removal studies have very modest effects on polarization. pnas.org/doi/10.1073/pnas.25…