Explain the following fact, Despite the fact that Bohr effect has a physiological advantage yet it has not been positively obeyed by some of the animals such as the human foetus and Arenicola (lugworm).

In contrast to mammalian haemoglobins the oxygen affinity ofArenicolahaemoglobin is increased by salts.

In case of the fetus contains its own special type of hemoglobin called fetal hemoglobin. Unlike the adult hemoglobin, fetal hemoglobin does not readily bind to 2,3-BPG and as a result has a higher affinity for oxygen (remember that by binding to the adult hemoglobin, 2,3-BPG decreases its affinity for oxygen)