How do humans collect animal sperm

fertility New theory: the egg cell decides which sperm is allowed in

We humans can turn ourselves upside down. Before coitus, or artificial insemination, when asked: Is he or she really the right person with whom I want to father children. After coitus, so that the sperm can find where it should go. Then when we drink this or eat that to help fertility. Everything so that the next pregnancy test shows the famous blue stripes. But in the end, all this would be wasted effort if the British-Swedish research team is right when they say that: in the end, the female egg cell decides which sperm it lets in and which it doesn't. Stockholm University's John Fitzpatrick explains what the study looked at:

Human egg cells release chemicals called chemoattractants. They attract sperm to unfertilized egg cells. We wanted to know if egg cells use these chemical signals to choose which sperm they attract.

And they also wanted to know: How do sperm react to the follicular fluid that surrounds the egg cells and which contains chemical attractants for sperm?

Woman says yes, egg cell no

So after removing the egg cells for artificial insemination, experiments were carried out with the follicular fluid of different women and it was checked whether this fluid might attract the sperm of one man more quickly than that of another. There were actually differences, to put it bluntly, it turned out that the woman can like the man - but the follicular fluid cannot prefer his sperm. A novelty for science, says Professor Daniel Brison. He is the Scientific Director of the Department of Reproductive Medicine at Saint Marys' Hospital, and the lead author of this study:

The idea that eggs select sperm is really novel in human fertility.

Daniel Brison, reproductive medicine specialist

Brison hopes the study result can help understand some of the unexplained causes of couple infertility. Professor Manfred Milinski from the Max Planck Institute for Evolutionary Biology in Plön in northern Germany does not believe that. He has been studying the subject of immunogenetics and the mechanisms behind the combinations of egg and sperm for years. Referring to the British-Swedish study, he says: In principle, the study shows nothing, except that sperm can travel at different speeds. In addition, under natural conditions after coitus, sperm cannot approach two different follicular fluids, or follicular fluids cannot decide between sperm of different origins.

Matching: The immune genes must complement each other

Why one or the other sperm reacts to a follicular fluid and is finally let into an egg cell has a completely different background for him: a biological process that ensures the evolutionarily most sensible "matching", that is, that the immune genes of a woman are mutually exclusive and complement men in the best possible way and give the offspring immune genes a wide range of pathogens.

But that's only the second step, because the first step is still taken by the people themselves who decide to want to become parents together. Even with this apparently conscious decision, an effective, evolutionary biological program takes place in the body: The decision is made through the sense of smell, as Milinski's employees demonstrated in the "T-Shirt Study" in the 1990s: women unconsciously select men who have other immune genes than themselves - via the sense of smell and then precisely those that complement their own immune genes.