When does linguistic ability develop?
One can easily look up information on when the heart, lungs, or fingernails develop in the fetus. We can tell when a baby takes his or her first breath. So why can we never pinpoint when the linguistic centers of the brain activate?
If my reading of Language and Responsibility is competent, Noam Chomsky argued in 1979 for recognition of linguistic ability as a function of the physical body no different from growing hair, teeth, or soft tissue. A fabulous idea, I think, if a bit hard to chew.
Chomsky's idea of a "universal grammar" means that underlying (physical?) structures in the human brain are receptive to linguistic acquisition. That also means that these receptors can turn on and off--like blood clotting, like fingernails always growing, like bones that reach a certain size and then stop growing--in ways we don't understand.
So, when do babies begin to understand language? When they begin to think in pictures? When they begin to understand relational concepts such as "in" and "upon"? When they begin to babble? Is the first word also the first step in the linguistic process? Or is it one of the last?