"Humans are social animals" is a phrase often repeated by psychologists to sum up why we've been such a successful species. Our ability to live, work, and cooperate in groups is the key to our survival. But it comes with a tradeoff. Companionship is an asset for human survival, but its mirror twin, isolation, can be toxic. Loneliness is associated with higher blood pressure and heart disease — it literally breaks our hearts. A 2015 meta-review of 70 studies showed that loneliness increases the risk of your chance of dying by 26 percent. (Compare that to depression and anxiety, which is associated with a comparable 21 percent increase in mortality.) Now researchers are trying to understand exactly how loneliness causes disease at the cellular level. And they're finding that loneliness is far more than a psychological pain — it's a biological wound that wreaks havoc on our cells. "Social isolation is far and away the strongest social risk factor out there," Steve Cole, a genetics