So what was it about the women's voices that gave away their reproductive status?The men in group one who correctly identified the menstrual recordings said they could tell by the mood (bad versus good), quality (harsh versus smooth), pitch (low versus high) and speed (slow versus fast) of the women's voices.But researchers have also shown that voices alone can be used to directly and indirectly predict characteristics like facial appearance, body type, physical strength and even sexual behavior.I think one of the most interesting results of the study is that across the board, men chose the menstrual voice around a third of the time. " It's a question most women have been asked at one point or another by their boyfriend or spouse during a disagreement.It turns out that some men actually can tell when it's a woman's time of the month—and it's not because of bratty behavior.Hormones induce the vocal changes that give women away."Vocal production is closely tied to our biology," Pipitone says of men and women.
Sending and receiving mixed signals is common in communication, especially between men and women who have just started dating.Males show more interest in females when they're fertile, so it makes sense that human females—who need a lot of help to raise their particularly helpless infants—hide their fertility status.(Female chimps, by contrast, broadcast their fertility with engorged genitalia.) Theoretically, human males retaliated by developing the ability to detect more subtle fertility cues such as those "leaked" by the female voice.Over time, the ability to parse a woman's menstrual cycle could have proliferated, as more perceptive men reproduced more successfully.Pipitone says the adaptation is an example of the reproductive arms race known as sexually antagonistic coevolution, a phenomenon seen across living species, from humans to brine shrimp.There's already evidence that men subconsciously judge where a woman is in her cycle—lap dancers make 80 percent more money in tips when they're ovulating compared to when they're menstruating, according to a 2007 paper—but the new study is the first to demonstrate one way men make that determination.