Why Do Humans Almost Always Retain Language?

I don't know if you've noticed. But whenever anyone gets brain damage, even at birth. Or even some congenital defect of the brain, they almost always retain their language. Some don't.

But could the reason by evolutionary? Because language would seem to me to be the most important human ability.

 

deepest grooves, most often used. only has become important because our cultures have so predominantly many come to be built around it.
i would have prefered it to have been painting on rock walls, but these aren't very accessable from hospital beds.