Photo: Sharat Ganapati/Flickr
Over the years I've written countless times on how the living difference between humans and the great apes is thinner than even the genetic similarities indicate. But a really interesting new study sheds light on one way in which chimpanzees and humans are indeed distinct.
It appears that even when human children are just two years old they already have an understanding of grammar—they aren't just imitating the adult's speech around them—whereas an older chimp that has been taught sign language doesn't get it. (You'll notice the use of the singular 'chimp,' which is an important qualifying condition to keep in mind here as we go through the research.)
Published in Proceedings of the National Academy of Sciences, Charles Yang's research looked at how two-year-old English-speaking children used articles; whether they really knew how they were using them, if they understood the grammatical reason for using 'a' versus 'the,' or if they were just mimicking the adults around them. He compared this usage to the abilities of Nim Chimpsky—the famous chimp that was taught to use sign language and was the subject of an extensive study on the language aquisition. Nim, who died at the age of 26 in 2000, acquired the ability to appropriately use 125 different signs over his lifetime.
There's some controversy over whether Nim's use of signs really constritutes language use, and whether it accuratly represents the ability of chimps to use language (Nim was raised away from other chimps, outside of a familial environment). Plus, here have been other chimps that have learned to communicate better than Nim. But that's a whole other discussion.
Nim Chimpsky catching up on the news. Credit: Herbert Terrace
If Nim's record is limited, so is that of 2-year old children. After all, the vocabulary of a two-year-old isn't large. But Yang found that by looking at how well toddlers put an 'a' or 'the' before a noun, he could get a glimpse at their grasp of grammar.
Yang found that young children growing up with English as their native language generally are error-free from the start in their use of articles. But whether or not this is because they are correctly mimicking adults or understanding grammar is another thing.
To sort out this problem, Yang examined the varying frequencies with which either the definite or indefinite article is used to produce a grammatically correct phrase. Due to the nature of the world, with any given noun there isn't a 50-50 chance of using either an indefinite or definite article. Yang uses the example of 'bathroom,' noting that 'the bathroom' is a more common phrase than 'a bathroom.'
Analysing young children's speech using a mathematical model, Yang found that "when you compare what children should say if they follow grammar against what children do say, you find it almost indistinguishable. If you simulate the expected diversity when a child is only repeating what adults say, it produces a diversity much lower than what children actually say."
When Yang ran the same analysis against the phrases than Nim put together, he found that Nim was not following systematic grammatical rules.
Which doesn't mean that Nim isn't communicating or doing it pretty well really (based on lists of Nim's quoted phrases), but it does suggest that it's at a lesser level of sophistication—and, as Yang points out, that children grasp abstract grammar at a very early age.
The real question is whether more data on chimps' ability to use sign language would change the results. Comparing multiple human children against one chimp, with whom there's some controversy, seems like a pretty considerable limitation. It is, however, an interesting start.