Old thesis established that the animals were able to adjust the composition of their ejaculate according to the risks of competition.
A study published in June 2005 this system expands to humanity. (in English at http://www.lwsimmons.org/ElectronicPapers/kilgallon_05.pdf)
The assumption was already at the base of the popular book of 1994 You Pr Robin Baker “Sperm Wars, the secrets of our romantic behavior”, writing along with very serious scientific publications.
Actually, before each ejaculation, man evaluates the risks of infidelity of his wife. These are more important, more sperm will be full of sperm.
Before all semen, recent study suggests to look at donor images where sperm competition is possible (2 for men 1 woman). However if one is some fierce competition, concentration decreases seminal.
The recent study has also helped to establish other parameters such as mobile phones brought to near the testes have a significant negative impact on concentration and sperm motility.
Under investigation, It also appeared that men raised in urban areas have more mobile sperm, that time the collection has an influence (not early in the morning !) Finally, men and couples who are sexually intense sperm have the most mobile.
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