Complex sentence: As so often in the history of science, sociological effects which are later made clear by experimental settings are already present in the language in the form of proverbs: birds of a feather, flock together.
Split into simpler sentences: As so often in the history of science, sociological effects which are later proved by experimental settings are already present in the language in the form of proverbs. This is true in this case as well: birds of a feather, flock together.