The findings suggest that the cycle of fertility is not as hidden in humans as scientists once suspected. It was previously believed women had evolved to hide their ovulation, rather than, like other mammals, going on 'heat'
A team from the University of Göttingen in Germany asked 28 women between the ages of 19 and and 33 to dance to the same drumbeat during the fertile late follicular phase of their cycles and the nonfertile mid-luteal phase. The team then showed 200 men, mostly undergraduate and graduate students, the silhouettes of the women dancing.
Even though the men had no idea that fertility was even being studied, the results showed they judged the fertile women as more attractive dancers than the others in their non-fertile phase.
Lead researcher Dr Bernhard Fink speculated that fluctuations in oestrogen - the female sex hormone, which can affect muscle, ligament and tendon strength - may have an effect on women's movements when fertile.
These qualities were picked up by the size and vigour of the movements of the upper body and arms, the researchers said.
But the findings showed that heterosexual men were also making use of these signals, presumably to detect love rival.
Northumbria psychologist Dr Nick Neave believes th
'Rated dance quality was positively associated with actual grip strength and these clues of upper-body strength were most accurately picked up by male observers,' he said.
'This ability to discern upper-body strength is principally because men are looking for cues of "formidability" in other males.
'Upper-body strength is highly related to fighting ability as it reflects the ability to do damage, especially in intra-sexual conflicts.
'The ability to gauge strength before potential conflicts is sensible, especially to other males.'
Also part of the research team were Northumbria University academics Dr Nick Caplan and Johannes Hvnekopp, with Bernard Fink, from the Institute of Zoology and Anthropology, University of Gvttingen, Germany.