Challenge instead of challenges

Dawkins then proceeds to single out Michael Ruse - a distinguished atheist philosopher who describes himself as a “hard-line Darwinian,” who has done much to clarify the philosophical roots and consequences of Darwinism, and challenge religious fundamentalism - as an example of such an appeaser.

Dawkin's God; By Alister McGrath

Dear forum members, why the verb "challenge" hasn't got "s"?

My guess is that "who has done much to" has been omitted.

Thanks.