Complex sentence: The rapid evolution of internal female and male reproductive morphology is due to the high sexual selection pressures characteristic of polygamous populations and so females can use cryptic female choice in choosing for or resisting males with specific physical or anatomical traits.
Split into simpler sentences: The rapid evolution of internal female and male reproductive morphology is due to the high sexual selection pressures characteristic of polygamous populations. In such cases, females can use cryptic female choice in choosing for or resisting males with specific physical or anatomical traits.