The small pear-shaped muscular organ that lies in the pelvic cavity (except during pregnancy) is called the

The answer is the uterus. 

The uterus is part of the female reproductive system. It looks like an inverted pear. It is also known as the womb. Normally, the size of the uterus is about as big as a fist but when a female is pregnant, it can stretch many times its size to accommodate the growing fetus. 

Yes it is hereditary because of the penis

Reduction in overall biodiversity