Fernando believes that behavior is strongly influenced by biology, is tied to evolution, and is characterized by critical or sensitive periods. he is most likely taking a(n) approach.

This is an ethological approach. In this viewpoint, behaviors are best described as being "all-natural," and are adaptive to their surrounds and cultures. In ethology, the researcher tends to use naturalistic observation moreso than laboratory conditions, which would be more apt to be used by the behavioralist researcher.