As Cheng points out, it’s a common tactic in nature, with many other primates – from rhesus macaques to our closest relatives, chimpanzees – lowering their vocal pitch during altercations. “It signals to others that their intention is to be ready to fight and protect their resources – to assert their status.” And the same connotations were apparent for the humans who had lowered their voices too. “They were rated by others as being more domineering and more willing to impose their will over others, and as a function of that, they were able to gather more influence and make decisions on the group’s behalf.”

Find out more: Does the way you speak give away how much you earn?

Cheng’s findings are certainly consistent with Pemberton’s hypothesis that greater gender equality explains the long-term vocal shift in those Australian women – a pattern that has now been recorded in Sweden, the US and Canada. Whether consciously or unconsciously, women appear to be adapting their vocal profile to suit the opportunities that are available to them today.

Interestingly, the influence of perceived dominance on vocal pitch can also be heard when you compare voices between countries. Women in the Netherlands consistently talk in deeper voices than women in Japan, for instance, and this seems to be linked to the prevailing gender stereotypes – independence versus powerlessness, for instance – in the different cultures (an inequality that is also reflected in a much larger gender pay gap in Japan).

And Cheng points out that these changing vocal dynamics may not always be an advantage for women, even in the countries where a deeper speaking voice is now more common.

“While lower voices – and other assertive behaviour in general – effectively signal and assert power and authority in women, as it does in men, it might also have the unintended effect of undermining how well liked they are,” she says, pointing to research showing that a deeper voice is considered to be less sexually attractive and less agreeable, for instance.

In this way, it could be another example of the “double-bind” that women face in the workplace, in which the very same qualities that are praised in men may still be judged negatively in their female colleagues. Just consider the media’s discussions of Hillary Clinton, who was considered either to be too “shrill” or too “unemotional”. The deeper speaking voices may be one audible sign of progress, but we clearly still have a long way to go before we eliminate those prejudices.

--

David Robson is a freelance writer based in the UK. He is @d_a_robson on Twitter.

To comment on this story or anything else you have seen on BBC Capital, please head over to our Facebook page or message us on Twitter.

If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Culture, Capital and Travel, delivered to your inbox every Friday.