Why can intersex animals self-fertilize but intersex humans are mostly sterile or infertile?

Intersex animals can sometimes self-fertilize due to their reproductive systems that may possess both male and female organs, allowing them to produce viable gametes and fertilize their own eggs. In contrast, intersex humans typically have complex chromosomal and hormonal variations that often lead to incomplete or nonfunctional reproductive systems, resulting in sterility or infertility. Additionally, the genetic and physiological differences between species play a significant role in the reproductive capabilities of intersex individuals. Thus, while some intersex animals can successfully reproduce, intersex humans generally cannot.