Too-powerful sperm cannot impregnate women, say scientists
Evolutionary changes mean that some men are producing super-sperm, which are too fast and powerful to fertilise women's eggs.
Oren Hasson, an evolutionary biologist, believes that modern infertility rates are due to these super-sperm, rather than men having too few sperm or their sperm being too weak.
The super-sperm are so powerful that they overcome the defences put up by the woman's body, resulting in more than one sperm penetrating the egg. This process, known as polyspermy, ruins the egg and prevents fertilisation.
Dr Hasson believes the new super-sperm are the result of an on-going evolutionary "arms race", whereby our bodies undergo subtle changes to improve fertility. But problems can arise if changes in men's bodies are not mirrored in women's bodies, as he believes is the case now, reports the Mail.
'Sometimes, during the fine-tuning process, high rates of infertility can be seen," he said. "That's probably the reason for the very high rates of unexplained infertility in the last decades."
Dr Hasson, of Tel Aviv University, studied fertility statistics and mathematical models, and concluded that the super-sperm evolved in response to changes in women's bodies creating extra defences to force sperm to be more competitive.
But the super-sperm are so fast they beat the blockade. In addition, men who produce weaker sperm, due to factors such as stress or pollution, have less chance of fertilising their partner.
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