That's the conclusion of a researcher at the University of South Australia:
Cecilia Pemberton at the University of South Australia studied the voices of two groups of Australian women aged 18–25 years. The researchers compared archival recordings of women talking in 1945 with more recent recordings taken in the early 1990s. The team found that the “fundamental frequency” had dropped by 23 Hz over five decades – from an average of 229 Hz (roughly an A# below middle C) to 206 Hz (roughly a G#). That’s a significant, audible difference.
The researchers had carefully selected their samples to control for any potential demographic factors: the women were all university students and none of them smoked. The team also considered the fact that members of the more recent group from the 1990s were using the contraceptive pill, which could have led to hormonal changes that could have altered the vocal chords. Yet the drop in pitch remained even when the team excluded those women from their sample.
Instead, the researchers speculated that the transformation reflects the rise of women to more prominent roles in society, leading them to adopt a deeper tone to project authority and dominance in the workplace.
I have a lot of friends who might agree; some of them sing soprano and speak tenor. No joke.