Look closely: this is history in the making. These are the clearest pictures ever taken of what is the starting point of every human life: ovulation occurring inside a woman's body. See the photos

"The release of the oocyte from the ovary is a crucial event in human reproduction," says Jacques Donnez at the Catholic University of Louvain (UCL) in Brussels, Belgium. "These pictures are clearly important to better understand the mechanism."

Observing ovulation in humans is extremely rare, and previous images have been fuzzy. Donnez captured the event by accident while preparing to carry out a partial hysterectomy on a 45-year-old woman. The release of an egg was considered a sudden, explosive event, but his pictures, to be published in Fertility and Sterility, show it taking place over a period of at least 15 minutes.

Shortly before the egg is released, enzymes break down the tissue in the mature follicle, a fluid-filled sac on the surface of the ovary that contains the egg. This prompts the formation of a reddish protrusion, and after a while a hole appears, from which the egg emerges, surrounded by support cells. It then enters a Fallopian tube, which carries it to the uterus.

While there are no immediate medical implications from the pictures, Darryl Russell, who researches reproductive health at the University of Adelaide in Australia, says they are remarkable: "In animals, even when we control hormone levels - allowing us to predict the time at which ovulation will occur - it is very rare to see it in progress."