The reality is that the universal grammar theory attempts to lay general structures that can be traced among languages. Therefore, if a constant 'X' is true then 'Y' will be equally true. It puts down how all languages expand when subjected to a given set of fundamental principles. With these principles, universal grammar enables us to try out word order prediction in languages, the phonemes, syntax etc. Several linguists hold that the universal grammar and its linkage to the other parts of the brain is the machinery that enables children to be fluent in whichever language in their childhood. This is the most critical stage of language learning in the life of human beings. It is also argued under this theory that children have a higher ability to learn second languages in natural settings than adults. Adults however, have a higher ability to consciously learn a second language in artificial settings such as classes.

Even though the nativists' theory holds water to some extent, there are underlying issues that works to the undoing of the theory. For instance there is no sufficient explanation behind the language disorder in some children. If the ability to acquire a language is innate, then all children should be able to learn the respective languages they are exposed to.

The other undoing is the noticeable difference is speed of language acquisition. If the theory is to hold universally true, then two or more children growing under the same condition should be able to learn the language they are exposed to with same speed. It is, however, noticeable that different children will have grasp of language at different periods of time. Indeed, some children will turn out to have a better linguistic aptitude than others with whom they grew in the same environment.

If the theory is to be regarded true, then it would be questionable how some children and adults still go ahead and acquire a second language. Having noted that there are pre-modeled grammar rules in the mind of the early language learners, it would ordinarily be expected that the grammar rules will hold and only the initial...

Is there then possibility of multiple grammar structures of different languages in the brain of language learners?
It is also not understandable how some life complications like stroke or Alzheimer's tend to wipe out the victims knowledge of the native language which they have been speaking for years. These victims still have brains and ordinarily, if the theory is to hold true, they would still retain the linguistic ability.

Conclusion

The social interactionists have attempted to resolve the impasse that existed (exists) between the nurture and nature proponents. They posit that while the infants and young language learners possess the inherent language capability in their brains, accommodative environment and experience are also paramount in language acquisition. Language is a product of nurture and nature working in tandem. If an n infant at birth is subjected to a situation where he lives in different environments every two months and moves to another and another, then language acquisition may not be possible even if they have the inherent capability. The environment may not have enough time to scribble in the tabula rasa some useful linguistic information within that short time.