What factor is suggested as a key determinant in the evolution of male reproductive anatomy across apes?

Answer

Sexual selection pressures acting on sperm production, which are driven by social complexity

The comparative data across apes suggests that the social environment dictates the level of sperm competition, which then serves as a primary driver for the evolution of traits like testicular volume.

What factor is suggested as a key determinant in the evolution of male reproductive anatomy across apes?
reproductionanimalanatomyPrimategorilla