The largest difference between old psychology and new psychology is the scientific method. Psychology has its roots in philosophy, and therefore psychological investigation began as reflection free from the constraints of the kind of experimentation seen in sciences such as biology and physics in the early days. Psychologists created their theories based on their perceptions and observations of others and their own personal experiences. The first branch of psychology to be subjected to quantitative experimentation was that of perception, the study of the senses. It was in the early 1800s that a call for a more scientific psychology was made. It was then that a merger between psychology and biology began to form whereby the function of the mind was to enable adaptation to the environment. By the late 1800s the new psychology had been established as a laboratory science in contrast to the old psychology, which was much more metaphysical in nature. Of the old psychology, however, still remains the observational nature of investigation. For instance, many a social psychology experiment consists of merely observing people interacting and reflecting on those observations.