Guys, if you're trying to lay blame for your pitiful mid-life crisis, some good news: Scientists have found that premature ejaculation is not all in your head. In fact, the propensity is genetically determined.

Neuropsychiatrist Marcel Waldinger and pharmacological researcher Paddy Janssen at Utrecht University studied 89 Dutch men who always suffer this problem, plus a control group of 92 men who are able to take their time. The study subjects' female partners actually timed them with stopwatches.

In men who suffer from premature ejaculation, the substance serotonin appears to be less active between the nerves in the section of the brain that controls the ejaculation. Among other things, this substance is linked to sexual activity and sexual desire. It is a substance that transfers a signal from one neuron to another. Due to the low activity of serotonin, this signal transfer does not occur properly in men with the primary form of premature ejaculation.

A gene which had already been discovered, namely 5-HTTLPR, appears to be responsible for the amount and activity of serotonin, which means that it controls the rapidity of ejaculation. Three types of the gene exist: LL, SL and SS. The study showed that the LL type causes a more rapid ejaculation. On average, men with LL ejaculate twice as quickly as men with SS, and also almost twice as quickly as men with SL.

The findings indicate the problem is not a psychological disorder, as some have suggested.

"The results of our research confirm the genetic theory and may contribute to possible gene therapy against premature ejaculation," Waldinger said. "This study applies to men who have always ejaculated prematurely from their first sexual contact onwards and not for men who started suffering from this later on in life."

The results will be detailed in the Journal of Sexual Medicine.