The fetus and placenta is not self but a mammalian/marsupial precursor animal that evolved live birthing instead of laying eggs co-opted genes from a virus that

The fetus and placenta is not self but a mammalian/marsupial precursor animal that evolved live birthing instead of laying eggs co-opted genes from a virus that enables the placenta to hoodwink the mother's immune system during gestation. This repair mechanism clearly forms part of the code cut-and-paste exercise.