Various mechanisms of physiological adaptation to adverse conditions have developed birds and mammals. A person has poorly regulated salt metabolism, and therefore he can not do without fresh water for a long time. But reptiles and birds, spending most of their lives in the open spaces and drinking sea water, have acquired special glands that allow them to quickly get rid of excess salts.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.