Reading a book first published in 1951, I am reminded that, at one time, the definition of
humanities included sciences of human behavior within its scope. Now, one seldom encounters that inclusion in contemporary use, and the Merriam-Webster Dictionary explicitly excludes the study of social relations (though it says nothing explicit about that part of behavior outside of the social).
In the earlier period, there was a question of whether the study of human behavior were fundamentally different from the study of the properties of other things. Those who insisted upon such a difference would speak and write of
science and the humanities as if of two separate things.
But the tools by which the physical, biological, and behavioral science were studied were increasingly shared. The physical and biological sciences took-up probability and statistics; the biological sciences have taken-up chemistry, mechanics, and game theory; the behavioral science have taken-up biological explanation and mathematical modelling. All have been affected by the same philosophic theories of method. A dichotomy of science and the humanities cannot prevail so long as the behavioral sciences are included amongst what are called
Apparently that dichotomy was so dear to some of those who insisted upon it that they attempted its preservation by implicitly changing what they intended with
humanities in order to hold fast to it. Of course, the newer definition doesn't maintain the original dichotomy; but replaces it with a new one.