Turns out that intelligent people are generally healthier than their less-clever peers - studies have shown that brainiacs are, for instance, less likely to suffer from heart disease and Alzheimer's. Scientists have suggested that smart people may score less stressful jobs in safer places and that they may make better lifestyle choices, for instance by exercising more and eating better. In other words, maybe bright people actually listen to the Surgeon General.
But these newest findings found that negative habits had little effect on sperm quality, so they don't support that theory.
The researchers instead speculate that intelligence might be passed down as part of a larger package of good attributes. One gene can influence multiple traits, so the genes involved in smarts may somehow improve sperm quality - and perhaps other characteristics as well.