|See larger version here.|
It's hard to read, so I'll read it off: we have economics on top, followed by sociology, then anthropology, and lastly, political science. The people have decided which subjects are most worth talking about!
I'm not well versed in the history of these disciplines to explain any patterns that may appear in these graphs, but there are some features of it that catch my eye. I find it fascinating that even though all the keywords started out neck-and-neck in the late 1800s, they ended up diverging completely. I'm also surprised to see political science at the bottom; though, admittedly, most of political science strikes me as recycled and refurbished economics/sociology.
Economics, of course, is king. I've heard professors (indirectly) explain why this is by saying that economics provides a really powerful predictive framework. It's because of this power, for example, that economics has a habit of colonizing areas of research that were previously the domain of other fields (e.g. Becker's study of crime coopted the study of deviance from sociology).
But I think another less-discussed reason why economics is so dominant is that the allocation problem is the most basic and most fundamental problem of society. It's the academic discipline that rests at the bottom of Maslow's Pyramid, as it were: first we want food on the table, a roof over our head, a way to earn a decent living, and then we can talk about the subtleties of cultural sovereignty.