Listening for love


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Secondary sexual characteristics are traits that are different in males and females and do not appear until sexual maturity. These characteristics advertise sexual maturity and, in the right combination, desirability. Humans have several secondary sexual characteristics, such as beards in men and full breasts in women. Another trait is that men generally have a deeper voice than women, or children. Previous studies have found that lower male voices are generally more attractive to women, but does this preference lead to a higher reproductive success? This question is virtually impossible to answer in industrialized countries, where the use of birth control skews reproductive fitness results.

Anthropologists were able to examine the relationship between voice and reproductive success in a population with no birth control. The Hadza are a hunter-gatherer society in Tanzania, and in a study published online September 25, 2007 in the journal Biology Letters, researchers set out to determine if Hadza men with deeper voices actually have higher evolutionary fitness, that is, if they father more surviving children.

They recorded mens' voices, asked them how many children they had, and how many of those children were alive. They found that the men with the lowest voices did in fact have the most children. Women from the same tribe said that better hunters had lower voices, suggesting that deep-voiced men might have more babies because women prefer them as mates and providers. The researchers also suggested that high testosterone levels could lead to both a deep voice and higher quality sperm, or that deeper-voiced men might be more likely to claim children as their own even if someone else was the biological father.

This study is the first to show a measurable relationship between voice and Darwinian fitness in humans, and it suggests how men could have evolved to have lower voices than women.


New Scientist news story (includes sound files of the mens' voices!)

Yahoo News story

BBC News story

Harvard news release

Author laboratory website

Original Paper
Apicella, C.L., Feinberg, D.R., and Marlowe, F.W. 2007. Voice pitch predicts reproductive success in male hunter-gatherers. Biology Letters

Questions for review and discussion

1. Define Darwinian fitness.

2. By conducting this study, what question about fitness did the researchers want to answer? Why did they choose a hunter-gatherer society for the study?

3. What data did they gather in order to answer this question?

4. The news articles mention three alternative explanations for why deep-voiced men had more children. What are these alternatives?

5. Can you think of any more explanations for the results? If so, what are they? What additional experiments could help clarify which of the explanations is most accurate?

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