A boyfriend once tried to see how long he could last in one session. That is as practically awkward as it sounds: 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. All sex really needs to achieve, it seems, is to put sperm into the vagina. Why do we have sex for so long? Why all the thrusting and bumping? So what did the researchers find? 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. Researchers in from the Kinsey Institute found: Penis size, virginity and fetishes: Getty "The basic storyline that has emerged from these studies is that, as we get older, our odds of developing chronic health conditions increases and this, in turn, negatively impacts the frequency and quality of sexual activity," wrote Dr. 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? For example, even though we like eating food, we don't chew each mouthful of it for five minutes just to make the enjoyment last longer. A study by researchers at Erciyes University in Turkey have found that overweight men last longer in bed. There are a whole host of factors which impact our sex lives, or lack thereof, including age, health, sex drive and lifestyle to name a few.