Do you want a kid? The first thing that you should do is to listen to your woman's voice because it signals her ovulation, as showed by a new research carried out by a team made of Nathan Pipitone and Gordon Gallup, of the State University of New York at Albany, and published in the Evolution and Human Behavior journal.

The researchers recorded women counting from 1 to 10 at four different moments of their menstrual cycle. These recordings were then played to a poll of young male and female subjects, who were asked to mark the attractiveness of the voices they heard. No matter the gender of the subjects who gave the ranking, the feminine voices were most attractive when recorded during ovulation.

"The results are in line with evidence that the female voice box, or larynx, is under the influence of sex hormones. The changes in the female voice during peak fertility support the view that women are "different" at that point in the menstrual cycle - in other words, that they experience estrus," said Gallup.

Monkey and ape females have a very obvious method of signaling fertility: buttock pads (ischial callosities), thick and brightly colored tissue around their genitalia. When a female is in estrus, the pads swell (sometimes to enormous sizes) and redden. There's very little subtlety to this.

Obviously, women lack this, relying in more discrete methods of signaling their fertility moments. Humans live in large societies, but they form monogamous couples, thus the human females must find a way to signal her estrus, but not with the purpose of attracting foreign males.

"Other differences include changes in sexual receptivity and odor sensitivity. The fact that men notice the differences in vocal attractiveness suggests that there is a subtle evolutionary battle of the sexes going on: as women evolve ever more efficient ways to conceal fertility - to avoid unwanted attention - men become increasingly sensitive to the tiny changes that do occur. Other women also pick up on the changes, perhaps to keep an eye on the competition," said Gallup.

"We have found that voices are higher in pitch on high-fertility days of the cycle," said Martie Haselton at the University of California, Los Angeles, co-author of another similar research.

"The voice changes might explain some of the shift in lap dancer tip earnings. Dancers certainly chat with their customers. But there is also evidence that visual attractiveness changes during the menstrual cycle. Voice quality is unlikely to be the whole story. Men can tell when a woman is most fertile, although the message seems to be conveyed by 'subtle behavioral signals' that evade conscious detection," said Geoffrey Miller from the University of New Mexico, Albuquerque, co-author of a 2007 research showing that women lap dancers get more tips during their ovulation days. The research did not detect if it was scent or other physical changes that attracted men, but it was clear that the dance moves in that period had something really special.

"The result fits with my findings that it's possible to detect ovulation through the effect of raised levels of estrogens on the way women walk and dance. It is highly possible that estrogen modulates motion abilities. It seems to be most likely that body motion - and not pheromones - is the information carrier." said evolutionary psychologist Karl Grammer of the Ludwig Boltzmann Institute for Urban Ethology in Vienna.