Structural change of northern populations (in constitutions, psychotypes and adaptive types) results from natural selection of people most effectively adapted to the North and readapted ones, i.e. having good adaptive capacity for these specific conditions. Organisms of many immigrants in northern regions in several cases (restricted time for adaptive processes and lack of functional, constitutional or mental reserves) are not able to adapt and function in the condition of increased functional power inputs. The resulting stress is reflected in reduction of functional reserves and undermined working capacity at individual and organismic level and in life expectancy at the populational level. Despite the human progress in the creation of technical protection means against the adverse environmental factors, adaptation remains one of the most important components determining the health condition of a person in the North. This problem is quite complex and many-sided and it is characterized by lots of contradictory scientific facts. In this article two aspects of the problem are discussed: 1) Structural change in northern populations (constitutions, psychotypes and adaptive types) resulting from the natural selection of people most effectively adapted to the North and also readapted ones, i.e. having good adaptive capacity in these specific conditions; 2) For unadapted people, activity leads to the reduction in functional reserves and working capacity at individual and organismic level and in life expectancy at the populational level.