Parasites are organisms that live in or on a host organism, obtaining essential nutrition for themselves from the host. Parasites rarely kill their hosts, however. Which explanation BEST describes why evolutionary pressures selected for parasites that do not kill the host?

Explanation:

the host is constantly creating more nutrition

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.