Hadza

Puts explains that men typically have deep voices as a result of high testosterone levels. High levels of this hormone cause the vocal cords to lengthen and thicken, and therefore vibrate at a lower frequency.

"Testosterone is associated with all sorts of things, like high libido and physical competitive ability," Puts notes. He adds that there appears to be a connection between testosterone and sperm quality, which might explain why the Hadza men with low-pitched voices fathered the most children.
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However, Apicella notes that some of the children listed by the Hadza men as being their own, might have in fact been fathered by other members of the group. This, she says, allows for an alternate explanation for her findings: "Maybe men with lower pitched voices feel more confident to say the children are theirs."