Anthropologists studied "the Hadza, a Tanzanian hunter-gatherer tribe that lives much the same way that most human beings did 200,000 years ago." The tribe does not use birth control, a factor which interferes with studies of reproductive success in modern populations. They found that males with lower voice pitch had more surviving children.
According to the article abstract they found that "men with low voice pitch have higher reproductive success and more children born to them" and hence "there is currently selection pressure for low-pitch voices in men," but that "voice pitch in men does not predict child mortality. These findings suggest that the association between voice pitch and reproductive success in men is mediated by differential access to fecund women," i.e. the chicks just prefer deeper-voiced guys.
The researchers found that "Voice pitch is not related to reproductive outcomes in women."