Fertility index

By Alison Motluk in Vancouver YOUR reproductive ability may be written in your hands. But what matters is the symmetry of your two hands and the length of your fingers, not the crinkles in your palms. Experiments in mice have revealed that mutations in a single gene, Hox, affected the development not only of digits but of ovaries and testes as well. So John Manning and his colleagues at the University of Liverpool decided to see if there was any link between hand shape and fertility. They measured the hands of 60 men and 40 women who were attending an infertility clinic. Some people had severe fertility problems, others were their healthy partners. Manning found that the men with the least symmetrical hands—where one hand is not a mirror image of the other—had the lowest sperm count and lowest sperm motility. “Digit asymmetry predicts the number of sperm per ejaculate,” he says. “The more asymmetry, the fewer sperm.” Twelve of his subjects, who were producing almost no sperm, had asymmetries of up to 4 millimetres between their hands. Manning also looked at the relative lengths of fingers. For reasons no one has been able to explain, men tend to have ring fingers that are longer than their index fingers, whereas in women the two fingers tend to be the same length. Manning found that men whose ring finger is much longer than their index finger tended to have higher levels of the male sex hormone testosterone, which plays a role in fertility. In women, by contrast, a longer index finger is associated with higher levels of the hormones oestrogen and luteinising hormone, both critical hormones for female reproduction. Manning thinks the relative lengths of the two fingers will be a robust predictor of fertility, but warns that more research is needed. Since the trait appears to be fixed in the womb, it may shed light on other developmental disorders such as autism. “You’re getting a window into the in utero conditions in that individual,
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