Single, widowed, and divorced people have as high as twice the mortality rate of married people, which is a trend that's held true in studies across countries and time periods. Unmarried peoples' tendencies to die seems to tell us about the relative strength of social bonds, which is supported by similar trends seen among ants, bees, and even cells, described in a fascinating paper in Cornell's quantitative biology archive.
In 1994, French entymologists found that insects in groups of ten live longer than those in groups of one or two. The survivorship curves for ants and termites looked like this, with the y-axis representing the percentage of survivors and the thin solid lines representing solitary bugs:
The same thing, it turns out, happens with cells, which die unless they get signals from their neighbors "telling" them to stay alive. This chart shows how smaller groups experienced more death.
Black = 1 million cells per mL; Blue = 100,000 per mL; Pink = 50,000 per mL
Getting to humans, similarly, mortality rate ratios for single versus married people (blue) and widowers versios married people (red) look like this:
So the effect tends to be stronger in men than women, with young widowers faring worse than older.
To see how consistent this pattern was, a group of physicists and etymologists got together, put insects in isolated groups (kept alive by "a tampon with sugar water which was changed every week") and waited for them to die. They found that, for the most part, single ants died much more quickly than ants living in groups of 10, with an average death rate that was about 2 to 3 times higher. A similar pattern seemed to occur for fruit flies, even though they're not thought of as social insects.
Death from isolation appeared to occur very quickly: in cells within 5 to 6 days of being kept in low concentrations; in insects 3 to 4 days after they were isolated; and in human widowers within the first year after the death of their spouse. The effect was seen as a "shock" as opposed to a smooth transition -- once isolated, cells, insects, and humans all die quickly. Just how quickly they died varied, though: the shock for ants was about 10 times greater than it was for fruit flies.
The researchers infer that the shock effect can indicate the strength of different organisms' social interactions -- the more dependent on one another they are, the more likely they are to die shortly after being isolated. Following that line of thought, they argue that young men are more closely attached to their wives than older men, because the death rate is higher among young widowers. "To say that the strength of a bond [of marriage] increases in the course of time," they explain, "is just wishful thinking." Their proposed rankings of our social ties, from weakest to strongest:
1. Fruit ﬂies
4. Married men over 50
5. Young married men under 30
While it makes for great metaphor, I'm not entirely sold on the idea that unmarried people are comparable to bugs that have been completely cut off from the swarm. But their list is fodder, perhaps, for meditations on the importance of sociability for all life forms, to say nothing of the researchers' incidental observation that the survivorship curves of ant colonies appear to closely resemble those of info-tech corporations. "If it can provide an incentive for further research," they write, "it will not be completely useless."