"War in the womb"

"The cells of the human endometrium are tightly aligned, creating a fortress-like wall around the inside of the uterus. That barrier is packed with lethal immune cells. As far back as 1903, researchers observed embryos ‘invading’ and ‘digesting’ their way into the uterine lining. In 1914, R W Johnstone described the implantation zone as ‘the fighting line where the conflict between the maternal cells and the invading trophoderm takes place’. It was a battlefield ‘strewn with... the dead on both sides’.

When scientists tried to gestate mice outside the womb, they expected the embryos to wither, deprived of the surface that had evolved to nurture them. To their shock they found instead that – implanted in the brain, testis or eye of a mouse – the embryo went wild. Placental cells rampaged through surrounding tissues, slaughtering everything in their path as they hunted for arteries to sate their thirst for nutrients. It's no accident that many of the same genes active in embryonic development have been implicated in cancer. Pregnancy is a lot more like war than we might care to admit...

That insight led Haig to found the theory of genomic imprinting, which explains how certain genes are expressed differently depending on whether they come from your father or your mother. Armed with this theory, we can see how conflicts of genetic interest between parents play out within the genomes of their offspring.

Because both parental genomes drive each other to keep ramping up their production of powerful hormones, should one gene fail, the result can be disastrous for both mother and infant. Normal development can proceed only as long as both parental genotypes are correctly balanced against one another. Just as in a tug-of-war, if one party drops its end, both fall over. This is one reason why mammals cannot reproduce asexually, and why cloning them is so difficult: mammalian development requires the intricate co-ordination of paternal and maternal genomes. A single misstep can ruin everything."

http://aeon.co/magazine/nature-and-cosmos/pregnancy-is-a-battleground-between-mother-father-and-baby/

#GenomicImprinting. This moves on the explore the uniquely aggressive system in humans and how it relates to the evolution of our brains. It also explains why primates menstruate so intensely (think about it - did any of your female pets growing up randomly bleed? I've always thought that was weird). 

This is deeply enjoyable science writing.