The nativists as well as the modern nativists focus primarily on the role of biological endowment of the child in the acquisition and development of language. The camp of nativism views language as an innate, species-specific capacity. The linguistic environment, then, only triggers the activation of this capacity. Nativism is supported by linguists such as Noam Chomsky, Steven Pinker, etc. You can read Eric Heinz Lenneberg’s Biological Foundations of Language for a detailed discussion.
According to the behaviourist theories, on the other hand, the child’s linguistic environment determines the course of development of language and even other abilities. Behaviourists consider “mind” to be a clean slate (tabula rasa)at birth, and language, like many other abilities, is treated as behaviour, which is gradually learnt from the environment. The child imitates verbal behaviour of parents and other language users around him or her. In this way, they are input and data-driven approaches to language acquisition and development. B. F. Skinner’s Verbal Behaviour is one of the most representative texts of such a theory of language acquisition and development. Hence, for nativists, humans are biologically wired with an abstract, language faculty, and for behaviourists, language is gradually learnt from linguistic environment.
The Interactionist theory of language development, supported by Lev Vygotsky, assumes a position somewhere in between the nativist and the behaviorist theories. According to this theory, language development is a product of the interaction of biological, cognitive and environmental factors. The Interactionists study the role of biological factors (Nativism) as well as the social and cultural influences from the environment (Behaviourism) in language acquisition and development.