So over the millennia that we have evolved, it's been a little bit like an arms race in the uterus, the lining getting thicker and thicker and thicker, and the embryo getting more invasive until we reach this détente with the lining of the uterus that we have.
Setelah berevolusi untuk beberapa tahun, ianya seperti perlumbaan senjata  di dalam rahim lapisan dinding rahim semakin menebal malah embrio pula semakin membesar sehingga ia menjadi satu dengan lapisan dinding rahim kepunyaan kita