Quirks & Quarks

A baby's cries can predict the sound of their adult voice

Children with finger lengths signalling they were exposed to higher levels of testosterone in the womb showed lower voice pitches in infancy as well as adulthood.
The pitch of a baby's cry ties its voice to what it likely be as an adult. (Wikimedia Commons)

Scientists have found that we can predict an adult's voice by listening to their baby cries. So the next time you hear a baby squeal, you're not just learning that they are hungry or tired, you're also learning what their voice will sound like as they grow up.

Canadian Katya Pisanski, a research fellow in psychology at the University of Sussex, has studied the voices of babies as they grew into children and as children grew into adults. She says the reason why there is a correlation between baby cries and adult voices lies in a baby cry's pitch.

Why pitch signals dominance

Pitch is an evolutionarily relevant trait, where lower-pitched voices are typically associated with  physical and social dominance. Pisanski explained that men with lower-pitched voices are often perceived as more dominant than higher-pitched men and:

  • Able to obtain dominant positions in society.
  • Win male-male conflicts.
  • Traditionally be chosen by females as mates. 

The difference in pitch between male and female voices is another consideration. Men's voices are typically only half the pitch of women's, while enormous variation is also found within the sexes. "These [differences] appear to emerge very early in life, as early as the first few months in life, as we see from babies' cries," Pisanski said.

But why would lower pitch be a signal of dominance?

Vocal pitch is related to the speed at which our vocal folds vibrate, and the formation of vocal folds is thought to be regulated by hormone levels inside the womb as a fetus is developing. Researchers have found that men with low-pitched voices typically have higher testosterone levels than those with high-pitched voices. The more testosterone the developing fetus is exposed to, the lower the pitch of their voice — once grown — should be.

Listening to future voices through distress cries

To test if this was really the case, Pisanski and her colleagues recorded the distress cries of babies in the first five months of their lives as they were taking a bath. Then they came back to these same individuals once they were five years old and recorded them speaking about a cartoon they'd watched.

They also measured something known as the 2D:4D ratio of each child, which is the difference in length between their second (index finger) and fourth digits (ring finger) on their right hand. Several studies have found that the 2D:4D ratio is a good predictor of hormone levels in utero. This measure provided insights into the hormonal environment these children were exposed to while their vocal folds were first being formed in the womb. 

As they anticipated, they found that a lower 2D:4D ratio in children was associated with higher fetal testosterone levels, lower voice pitches in infancy as well as in adulthood.

About 40 per cent of the individual voice pitch differences at age five could be predicted by their voice pitch at four or five months of age. 

Previously, the team found that boy's  voice pitch at age seven predicts up to 56 per cent of the variance that is found in their voice pitch as adults. In this sense, our vocal pitch — the seed for which gets planted in utero — stays significantly similar over time.

So far, Pisanski said there's "good" evidence for predicting pitch in human males and "some" for females. (Scientists haven't sampled or followed as many girls.)

Babies don't have vocal fry

However not all of our vocal pitch formation can be explained by hormones in utero. Environmental factors like smoking and even which language you speak can shape your pitch as well.

Several studies in the last few years indicate we might even be manipulating our pitch on purpose to appear more dominant and competent in modern daily life. Some young professional women in urban centres have been found to lower their vocal pitch so much that they enter what's been called the "vocal fry" register — their lowest register. It sounds a bit like croaking or scraping the voice.

Whether vocal fry causes its performers to be perceived as more or less empowered, and whether or not that perception is affected by listeners understanding it is a performance rather than an inherent trait, is still an open question that Pisanski hopes to test.