London, Sep 3 (IANS): Contrary to what one might expect, researchers have found that facial masculinity is negatively associated with semen quality.

So, if you want to make healthy and intelligent babies, do not blindly scan through handsome faces to decide your partner.

"As increased levels of testosterone have been demonstrated to impair sperm production, this finding may indicate a trade-off between investments in secondary sexual signalling (facial masculinity) and fertility," researchers said.

Using a new technique called Phenotype Linked Fertility Hypothesis (PLFH), the study investigated whether potential ability to select fertile partners is independent of factors such as sex and cultural background.

During the study, 62 Caucasian male students from the University of Valencia, Spain, were recruited.

All the males were asked to abstain from sex and masturbation for three to five days prior to the semen collection.

Semen analysis for 50 males was performed after liquefaction of ejaculated semen.

Sperm motility and concentration were measured according to the World Health Organisation criteria (WHO).

Each male subject was photographed for frontal and right-profile facial photographs.

All the colour photographs were scanned and a black oval mask was placed over the images to minimise the visual effect of hairstyle.

"Interestingly, males estimated the facial images to be more attractive than females, suggesting that males generally overestimate the attractiveness of other men to females," researchers noted.

This suggests that male facial cues may provide culture and sex-independent information about male fertility.

"Our results also indicate that humans may be more sensitive to facial attractiveness cues within their own populations," the authors concluded.

The study appeared recently in the Journal of Evolutionary Biology.