Among new PhDs in the humanities who described their dissertation research as interdisciplinary, philosophy students reported the largest percentage of dissertations that crossed fields rather than partnering with another humanities discipline (over 50% in the 2011–2013 cohort), compared to less than a third in the other humanities disciplines… In more than a third of the interdisciplinary philosophy dissertations produced by the 2011–2013 cohort (35.2%), the secondary field was social sciences. Another 12.1% of the interdisciplinary dissertations in philosophy were reported as drawing on the life or physical sciences. In all other humanities disciplines, the percentage drawing from the life and physical sciences was three percent or less.

So reports the American Academy of Arts and Sciences via its Humanities Indicators project:

The project also reports that in the humanities, “the proportion of doctorate recipients reporting interdisciplinary research rose rose from 26.5% in 2003 to 43.5% in 2012.” The rest of the report is here. (Via Inside Higher Ed)