Pinker on heredity, environment and language

First, to reassure the nervous: yes, there are important roles for both heredity and environment. A child brought up in Japan ends up speaking Japanese; the same child, if brought up in the United States, would end up speaking English. So we know that the environment playes a role. If a child is inseparable from a pet hamster when growing up, the child ends up speaking a language, but the hamster, exposed to the same environment, does not. So we know that heredity playes a role.

Steven Pinker, Language Instinct, HarperPerennial, New York, 1995, p. 408.