We all know that babies are voracious learners and easily acquire language and that it gets harder to learn as you grow older, but this Guardian article by Nathalia Gjersoe puts it memorably (and doubtless oversimplifies the science) in the course of debunking the myth that the average person only uses 10% of their brain:
But resources are limited and the brain is incredibly hungry. It takes a huge amount of energy just to keep it electrically ticking over. There is an excellent TEDEd animation here that explains this nicely. The human adult brain makes up only 2% of the body’s mass yet uses 20% of energy intake. Babies’ brains use 60%! Evolution would necessarily cull any redundant parts of such an expensive organ.
From studying the development of the brain in babies, scientists know that pruning back connections can be just as important as forming them. Shortly after a baby is born there is an exuberant proliferation of connectivity between the neurons followed by rampant pruning of pathways that are underused. During peak pruning periods, it has been estimated that as many as 100,000 connections may be eliminated per second. This is the second principle of neural connectivity: use it or lose it!
As an example, all babies are able to discriminate any language phoneme (the basic sounds that make up a language) until 6 months of age. After this they become increasingly tuned in to just those phonemes used by their local language. This enables babies to more swiftly learn their native tongue. Japanese does not distinguish between |l| and |r| so adult English-learners struggle to even hear the difference between these two phonemes.
Any unused parts of the brain quickly die off to free up resources needed to strengthen those connections that are most often used. This tunes the brain to be exquisitely well adapted to specifically the environment it finds itself in. In this light, the idea that 90% of the brain is lying dormant, waiting for some product, program or drug to access it, seems ludicrous.
Thanks for the link, Bathrobe!
Addendum: A useful companion piece is this New Scientist review by Alun Anderson of The Language Myth: Why Language Is Not an Instinct by Vyvyan Evans, which sounds like a good book:
The commonplace view of “language as instinct” is the myth Evans wants to destroy and he attempts the operation with great verve. The myth comes from the way children effortlessly learn languages just by listening to adults around them, without being aware explicitly of the governing grammatical rules.
This “miracle” of spontaneous learning led Chomsky to argue that grammar is stored in a module of the mind, a “language acquisition device”, waiting to be activated, stage-by-stage, when an infant encounters the jumble of language. The rules behind language are built into our genes. […]
They may have been chasing a mirage. Evans marshals impressive empirical evidence to take apart different facets of the “language instinct myth”. A key criticism is that the more languages are studied, the more their diversity becomes apparent and an underlying universal grammar less probable.
And the hat tip for that link goes to John Emerson.