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Living on the edge

Russian zoologist V.V. Khlebovich is trying to understand why different species of animals have similar temperature and osmotic pressure of their internal environment, and why these internal conditions are threateningly close to being fatal.

A permanent state of salinity of the internal environment is a considerable evolutionary acquisition. It enabled animals to leave the sea and settle in previously inaccessible freshwater and then move onto the land. To do this the animals had to create a mechanism to ensure a constant inner salinity for their cells and tissues of at least 5-8%.

Constant body temperature is an achievement that has been studied more than constant inner salinity, although it is a lot younger. It is only possessed by birds and mammals which have therefore been able to assimilate the higher latitudes and which are active at all seasons of the year. Their internal temperature is between 38 and 40 degrees. Obviously it is this temperature that has its advantages, but it is also very dangerous as it is close to a lethal level.

Therefore, the body temperature and inner salinity selected by animals are very close to the limits of stability in protein complexes. Khlebovich believes that it is in this dangerous feature that biological processes take place at an optimum level, and it is this level that is easier to control. Such a situation is a particular expression of a more general principle, in accordance with which any process is simpler to regulate near to critical point, such, for example, as the controllable nuclear reaction of decay or synthesis.