A combination of both innate capability and environment is necessary for language acquisition. The vast majority of humans have the innate capability to acquire language, unless they incur some form of damage to the language centers of the brain. On the other hand, those who have not been exposed to any language at all when young, at a time the brain is still plastic, are unlikely to be able to acquire language at a later time. People raised in a linguistically enriched childhood environment are likely to be more skilled at language use than those for whom this is not the case. Finally, those who learn second  languages as adults are less likely to acquire near-native speaker fluency (especially accents) than those who learned those languages as children.