Reporting their findings in the journalIntelligence, researchers from the Institute of Psychiatry in the UK say that men with higher intelligence tend to produce better quality sperm. This, say the researchers, suggests a closer-than-expected relationship between intelligence and evolutionary fitness.
The intelligence/sperm analysis was conducted as a precursor to possible further study involving the associations between intelligence, health, fertility, and overall fitness. In other words, the likelihood of surviving and reproducing under evolutionarily-typical conditions.
The data came from more than 400 former US soldiers who had undertaken detailed intelligence tests and also provided semen samples. The researchers examined the relationships between intelligence, semen quality (sperm motility, sperm concentration, sperm count), age, and the main lifestyle factors known to predict health: obesity, alcohol, tobacco, marijuana and hard drugs.
Arden thinks that there may also be another reason for the link and that intelligence may indicate underlying, genetically-based biological fitness. The reason, explains Arden, is that genes influencing intelligence might also contribute to hundreds of other characteristics. If so, tiny mutations that impair intelligence may also harm other characteristics. We all carry thousands of mildly harmful mutations, but some people carry more than others. More mutations may cause lower intelligence and worse health.
“We were interested in testing the idea that if most of our genes act on many characteristics, there might be a weak, but discoverable, relationship right across all of our characteristics – from nose to toes. This set of weak relationships would give rise to a ‘fitness factor’ in evolutionary terms,” concluded Arden.