except they are parasites. for women, biologically, the foetus considers the mother's body as the host body and siphons off resources. and thats ok. because the parasite is 50% of host DNA.
all babies are born premature because we evolved quickly and the human female's pelvic bones didnt grow as wide and as quickly as the baby's head to come through the birth canal. even after birth, the human baby needs the mother/father for a much longer time for survival.
progestrone, semen, testosterone, pregnancy etc hijacks not just the blood stream, hormones but also the brain because the fetus basically converts the mother's body into a fortress and a machine to keep itself alive. after birth, the immature baby/fetus also hijacks the father's brain and instincts.
it's best to remember that all biological organisms are mere vehicles for DNA and it's survival instinct. this isnt just for humans. my favourites are insects. at the farm..watch the praying mantis and the tarantula wasp and the drone bees play out their lives changes your perspective on life forever.