Does gerrymandering cause polarization?

I used to think so, but not any more:

We assess whether there is a strong causal relationship between congressional districting and polarization. We find very little evidence for such a link. First, we show that congressional polarization is primarily a function of the differences in how Democrats and Republicans represent the same districts rather than a function of which districts each party represents or the distribution of constituency preferences. Second, we conduct simulations to gauge the level of polarization under various “neutral” districting procedures. We find that the actual levels of polarization are not much higher than those produced by the simulations. We do find that gerrymandering has increased the Republican seat share in the House; however, this increase is not an important source of polarization.

That's from the very accomplished Howard Rosenthal.  The paper is here, hat tip to BookForum. 

So what does cause voter polarization?  Here is a counterintuitive hypothesis: political extremists are most active when they fear that the extremists from the other side might win.  Each candidate requires those extremists for support and resources, and when a candidate wins he or she then must polarize to some extent.  If you think of the extremists as motivated by fear of the other side, in a lopsided district they are more likely to stay at home and keep their mouths shut, thereby allowing the candidate to straddle the center.  It's a close race that brings out the partisans and gives them some measure of ex post control.

Might this be true?

We examine DW-Nominate scores for members of the House of Representatives who served from 1993 through 2000. The most politically extreme members tended to represent politically competitive districts, a result at odds with traditional Downsian expectations.

File this one under "I'm still fundamentally confused."