When you and I were foetuses in our mothers’ wombs, we needed oxygen, which we extracted from our mothers’ blood via the placenta. This requires a special type of foetal haemoglobin, which binds oxygen more tightly, and hence can grab it from the adult haemoglobin of the mother. Foetal haemoglobin is made by replacing the two adult beta globins with two gamma globins. In this case, gene duplication and subsequent specialisation provided a necessary step on the path that culminated in the placental mammals.
