I shared this on Facebook, and my friend who's a perinatologist (a sub-specialist who takes care of moms delivering preterm, moms w severe medical conditions (lupus, kidney failure, heart failure) and fetuses with problems (birth defects, fetuses who need transfusions for anemia) commented, saying, "The fetus is the most successful parasite known to man. Many people even want one!"
From a purely technical viewpoint, parasitism is always antagonistic/bad.
If not, it's called mutualism or commensalism. Not disagreeing with your real point, just being pedantic.
edit: to biomcgary, two points: first - i was taught that parasitism is by definition bad but actual interactions between species can fall along a spectrum of mutualistic and parasitic (and individual and specific effects may differ). second - it really ought to be moot since these terms refer interspecific interaction, right? I did a little googling before this edit, and yes, i see intraspecific brood parasitism and such... anyway, enough digression from me. I just think it's an overly-clever corruption of the actual concept of parasitism to describe a fetus as one. It's like calling a hill a parasite because it takes effort to walk up one.
You may be trying to be pedantic, but, to be meta-pedantic, your point highlights that two different conclusions are reasonable depending on the scale of analysis. At a functional level, a fetus takes nutrients from mom without returning any benefit (thus a parasite), but from the longer term perspective of evolution the relationship is mutualistic.
Thanks for the 4 downvotes so far. I have a formal education in biology and my points were correct. Sorry about the tone. I guess we're valuing style over substance now.
