Incidentally, this could explain why it becomes painful for a man to continue thrusting after ejaculating, since that would risk scooping out his own semen as well. Why we last so long is a pretty complicated question with no clear answer, but a clue may be in the way the penis is shaped. Instead of sliding the penis in and out many hundreds of times per sexual session, why not just put it in once, ejaculate, and then go have a lemonade and get on with the rest of the day? What this suggests is that men's repeated thrusting might function to displace other men's semen before ejaculating, ensuring their own swimmers have a better chance of reaching the egg first. What about just asking people how long they take, you say? Before you say, 'because it's fun to go in and out', remember evolution doesn't care about fun per se — it generally only 'designs' things to be enjoyable if they helped our ancestors pass on their genes to future generations. My advice would be to try not to think about it during the throes of passion. Blinded Timer Device As mentioned above, subjects in the first study used stopwatches to measure the amount of time they spent on each IELT. But science is rarely perfect, and this is the best we've got. What about just asking people how long they take, you say? The average median, technically across all couples, though, was 5. That's an fold difference. One is that people are likely to be biased upwards in their time estimates, because it's socially desirable to say you go long into the night. There were significant variations between countries, though; men in Turkey had considerably shorter IELTs 3. The study interviewed sex therapists in Canada and the U. Measuring an average time to ejaculation is not a straightforward matter. The most striking result is that there was a huge amount of variation.