Geoffrey Miller recently published research which clearly shows that human males can detect whether or not females are fertile. The data support the conclusion that males can detect whether or not females are ovulating, even if they don’t know that that’s what they are detecting. His unusual study took place in lap-dancing clubs and the measure of detection was how much the men tipped the dancers. The conclusion: a woman is sexier when most fertile. His paper Ovulatory cycle effects on tip earnings by lap-dancers: Economic evidence for human estrus? is here and you can read a synopsis by The Economist here.
The research doesn’t say how males detect the fertility of females, but the data certainly illustrates that our communication is far more comprehensive than words alone and animal instincts play a large part in economics.