Final answer:
The professor's later contributions were made in a 'Collaborative' manner, reflecting the interdisciplinary and team-based nature of modern academic and scientific work.
Step-by-step explanation:
The professor mentioned in the question initially made a name for himself by independently creating a theory in his field. Later in his career, his contributions were made in a more collective manner. From the details provided, a suitable adjective to describe the nature of his later work is b. Collaborative. This change from independent to cooperative work is echoed across various disciplines including sociology, conservation biology, and astronomy, where scholars such as Peter Raven, Paul Ehrlich, and Henry Norris Russell developed methodologies and made significant contributions through teamwork, cross-disciplinary efforts, and academic exchanges.