Boys produce more speech in their first year

The unmistakable noise of a young child trying to talk. But, somewhat surprisingly, researchers at the University of Memphis say that boys are more likely to produce these speech-like vocalisations in their first 18 months than girls, and it’s all to do with boosting their survival rates. Kim Oller is a professor at the University of Memphis and is behind the study, which happened almost by accident…

Kim - We didn't know that we were going to be interested in studying sex effects. We gathered data on early vocal development and we happened to have lots of boys and girls. And just by chance almost, ran an analysis comparing the boys and the girls. We were surprised to find that the boys were actually vocalising more than the girls in the first year. And the reason that's a little surprising is that there is a very widespread belief that females have an advantage in language. And so we had thought if there would be a difference between boys and girls, that the girls would be favoured and they weren't.

Chris - Of course there's a difference between vocalisation and language. So is there a distinction there in your study? Boys make noise, but it's the girls that later maybe emerge as the the stronger linguists?

Kim - Yeah, that's a good point. All that we see in the first year in these vocalisations we think of as precursors to speech is an emerging capacity and inclination to use the voice.

Chris - How did you get this data? I know you said this was opportunistic, but how did you come by all these recordings in the first place and how many recordings did you have?

Kim - 450,000 hours of recording. And the way I got in contact with it was through an organisation that I've been working with for almost 20 years now. It's called the LENA Foundation. They've produced a recording system, a little iPod size recorder, that you can put in the vest of a child's t-shirt and it will record all day long what the baby does. And they have also developed a way of using automated analysis so that they can count the number of vocalisations the babies are producing and they can count the number of what we call conversational turns, times when the baby says something and someone else says something within five seconds of that. So we acquired these data by automated analysis of these 450,000 hours of recording.

Chris - Let's break it down a bit then. So who was saying what at what age and how did the boys and girls differ?

Kim - What we're interested in, of course, is the sounds that are actually thought to be precursors to speech. Those were produced at rates of two to three per minute, and that's true of both boys and girls, except that the boys are 9 to 10% more vocal than the girls in the first year.

Chris - And is that the crossover point where the girls begin to take over? At the one year point? The boys dominate for that first year, and then there's a switchover?

Kim - In this particular study we saw the girls begin to show a significantly larger rate of vocalisation by about 18 months, something like that. So it's towards the end of the second year that the girls finally take over.

Chris - Was that interaction drive? Can your recordings reveal whether it's just that the parents are chattier with the girls, perhaps because they do something that solicits that chattiness and that elicits the response from the baby girls more than the boys? Or was this just spontaneous vocalisation that dominated in the boys for the first 18 months and then switches into a female dominated picture after that?

Kim - It should be clarified that the data showed that people were talking in the neighbourhood of the girls more often than the boys across the whole two year period. So the tendency for boys to be more vocal did not correspond to a tendency for parents to talk more in their neighbourhood in the first year. Now, as for why it would be that the boys would show more vocalisation in the first year, we think that's associated with the tendency of boys to be more vulnerable to dying in the first year than girls are now. This appears to be pretty much universal in humans. Boys are just more fragile in some ways, presumably because of immunological differences between boys and girls dying in the first year, and the rate of death of infants in the first year is much higher than it is in subsequent years. Consequently, we think that the rate of vocalisation that boys are producing in the first year being higher than girls in the first year has to do with the fact that they are signalling their wellness with vocalisation and in some sense eliciting more care for them in the first year by their parents.

Chris - What do you think the mechanism of this is then? Is it reflected in the way the brain wires itself up so that in males there is some kind of preferential wiring to make these vocalisations, which is then outcompeted or outpaced by female nerve development, which catches up and then surpasses the boys once they get beyond that vulnerable window period you've just outlined?

Kim - The way we reason about this is that humans vocalise so much in the first years of life because humans are born in a way where they have to be taken care of by caregivers. They can't get their own food, they need protection. The reason they vocalise so much is presumably that they have been naturally selected to use vocalisation as a way of signalling their wellness, because caregivers will invest in babies that they think are the most viable. And so any signals that they could produce that would suggest I am well and better than my brother would be selected for. And in the case of boys, it's particularly important that they signal their wellness in that first year because they're so vulnerable to die.