A baby throws up his arms asking to be picked up, points at an object to answer a question or quiets himself when his mother puts her index finger to her lips to make the universal "shh" sign.
Using and understanding hand gestures is one way babies start to flex their communication muscles before they can speak.
New evidence suggests that the better a baby is at grasping the meanings of these hand gestures, the better his or her vocabulary will be by preschool age - which is itself a known predictor of future academic success.
The new study out of the University of Chicago, which appears today in the journal Science, also found that children from higher socio-economic backgrounds have a distinct advantage over those from lower-income backgrounds. They gesture more as babies and have larger vocabularies at age 4½.
Study co-author and developmental psychologist Meredith Rowe said more research is needed to determine whether it's possible to manipulate how frequently parents and babies are inclined to gesture, but the potential implications are intriguing.
"Can you get parents and young children to gesture more when they're communicating? And if you can, will it lead to an increase in children's vocabulary?" said Dr. Rowe, a postdoctoral scholar at the university.
To measure the use of gesture, Dr. Rowe and her colleagues filmed 50 14-month-olds and their primary caregivers for 90-minute sessions, then transcribed the use of words and gestures by both caregivers and babies.
About 70 per cent of the moves involved pointing at objects. Conventional gestures such as waving, shaking the head and the two-armed "up" gesture accounted for about 20 per cent of the moves recorded.
A third category covered more representational gestures, such as flapping the arms to represent flying. (Babies at 14 months haven't mastered this style of gesture, but their parents use it. Children start to mimic them at about 26 months of age, Dr. Rowe said.)
Researchers counted the number of meanings connected with the hand gestures, rather than the total number of gestures. For instance, Dr. Rowe said, a baby pointing at a dog 10 times would be scored as a single gesture meaning.
"We were looking for the diversity of objects being portrayed."
The children were assessed again at 54 months with a standard vocabulary test.
The study also took into account the socio-economic status of the parent or primary caregiver, on a scale of 10 to 18 education years, with 12 years being equivalent to a high-school degree. The average family income of the participants ranged from $15,000 to $100,000 (U.S.) per year.
The most striking finding, Dr. Rowe said, was just how connected the early use of gesture was with socio-economic status.
At 14 months, children of families with higher socio-economic status are producing an average of 24 different gesture meanings during 90 minutes, compared with about 13 meanings from those with less affluent backgrounds.
At age 4½, children from higher-income families understood about 117 words, whereas children from lower-income families scored about 93.
"We can explain some of that gap by looking at how a child and his or her parents are gesturing several years earlier," Dr. Rowe said. "When children are 14 months old, before they're even saying much and before we see socio-economic differences in their speech, we're seeing socio-economic differences in their gestures," Dr. Rowe said.
The study also found that a baby's gesture vocabulary mirrors that of the parent or primary caregiver, which could explain the relationship to the parents' income and level of education, Dr. Rowe said.
The findings are "an indication that we really need to look at what's going on at home or during the early childhood period to try and figure out how that gap's getting created," Dr. Rowe said.
It's not that higher-paid, more educated parents are magically producing more gestures, she said, but that they are instilling more meanings with gesture.
Gesturing could play a role in learning words by eliciting and reinforcing vocabulary from parents. In response to a child pointing at a doll, the parent might say, "Yes, that's a doll," for instance.
The connection may also be more direct, the study suggests. Gestures may allow children to use their hands to convey meaning if they have difficulty uttering words.
Previous research has found that lower-paid and less-educated parents tend to talk less to their children, she said. Gesturing may follow the same pattern - but show up much earlier than speech.
"The key here is that it's the gesture in the children at 14 months that helps explain that socio-economic gap in their vocabulary later on."
