"Aim for at least three stable close relationships Anthropologist Joan Silk's research on female baboons found that those with a core group of female friends showed lower cortisol levels, lived longer, and had more surviving offspring, with "at least three stable relationships" identified as the threshold that produced these benefits. Pinker applies this directly to humans, noting that "these in-person friendships create a biological forcefield against disease and decline" — women with breast cancer who have close social ties are four times more likely to survive than those who are socially isolated. Knowing there is a specific, achievable number gives anyone a practical audit: count your reliable relationships and actively invest in building toward three if you are not already there. Source: Susan Pinker, TED Talk, The Secret to Living Longer May Be Your Social Life"