Some anthropologists in the Amazon claim to have located a tribal language, Piraha, which has no words for numbers, no fixed words for colors (you simply compare colors to other things similar in color) and a disdain for abstract concepts generally (see also here). This would be a powerful argument against the claims that we are hard wired with universal linguistic building blocks, a claim associated in particular with linguist and media critic Noam Chomsky.
Of course, there is reason to doubt evidence that claims to go to the very human condition, based on the observations of a handful of people in a community that has only a couple of hundred speakers in the middle of the Amazon jungle. One first has to assume that the researchers, who have a bold theory to advance, haven't been colored in their judgment (for example, there are real doubts about the accuracy of their no color word hypothesis). And, since inabilty to learn numbers is a key basis for their conclusion, poor teaching by the small number of available teachers could be as important as inability to learn.
But, suppose that their reports are true. This doesn't necessarily mean that language abilities aren't hardwired in some kind of universal grammar. This could be an exception that proves and refines slightly, the rule. Many natural human tendencies are use it or lose it. The congentially blind reorganize their minds to put vision centers to other uses, even though most people would consider vision to be a hardwired characteristic. A child forced to grow up without human contract grows up maimed emotionally to the point of near death or total inability to function, even if the child's physical needs like food and water and warmth are provided for by caretakers. It is hardly a stretch to argue that a uniquely primative environment in the midst of a jungle far from other human societies might be so devoid of the right kind of stimuli that it causes hardwired tendencies to understand numbers, colors and abstract concepts to atrophy.
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