Semen during pregnancy

For the paper you shared with us, it was an interesting hypothesis. Having semen that killed the fetus of another man could also ensure the long-term partner providing resources is increasing his fitness and not another man's. However they didn't mention female cheating. Children from monogamous relationships are around 25% likely NOT be fathered by the man in the relationship. I don't have time to check the paper's references to see if they did actual paternity tests but I would think that would be important if the mother had a primary long term partner and an occasional secret secondary partner.

On another note, in one of my graduate classes, a medical evolutionary biologist was talking to us about his field. The preeclampsia slide was interesting because he talked about one hypothesis where preeclampsia is a battle between the mother and fetus. A woman's child increases her fitness and increased resources increases the probability that the child will go on to reproduce. However, the fetus is only 1/2 related to its mother and it is in the fetus's best interest to extract as much as possible, even to the detriment to the mother (and her future reproductive potential). The battle is between the fetus trying to increase its resources and increased development (me me me!) and the mother to increase her lifelong fitness (i.e. more children than simply the one child she is carrying). With this in mind, a fetus who extracts resources to the detriment the mother and the mother reacts to reduce the drain on her. Vice versa, a mother who "rations" her resources to her child might force the fetus to try to extract more resources from the mother. Again, I don't have the time to verify this in the literature, but the two hypotheses could possibly be fairly complementary.

for what its worth i came close to pre-e w/my 2nd baby, and her dad is not my 1sts dad. i was horribly sick.

All these analyses seem to be hung up on the idea that it is the content of the sperm or some other physical/biological cause for the reduction of birth defects or decrease depression. Perhaps it is simply the fact that humans have evolved higher brains with the capability to emotionaly experience each other on a different level. What I mean here, is that sex (particularly monogamous where one can count on the other) brings the couple emotionally closer and more together. This monogomy therefore reduces stress (since there is someone to emotionally lean on) and thus cuts risk for all sorts of illness (as stress increases risk for everything..cortisol...) and increasing survivability, and so, being selected for evolutionarily since those that practice monogomy would have a better chance of having healthy children and passing on their genetic traits - including their tendency for monogomy. But more than this, even without looking through the prism of evolution; it would make sense that a species with a higher brain capacity would choose an activity which is pleasureable and brings partners closer all year round and after ability to give birth - not just when the hormones are at their peak like other species. Also a smarter species would more often choose stability and security over gambled pursuit of increased love options, since they have the brain capacity to analyze and understand the longterm benefits and not just go with the instant gratification route.