On the great number of observations the authors demonstrate, that children of different birth number have different biological qualities. For the Carpathian population the optimal sanological number is the fourth. The fourth children have the greatest vitality. The firstly born children are, usually, the most weak and have the least vitality. The difference in the sick and mortality rate of the first and the fourth children is so great, that the change of the weight of children with optimal birth number in the population may change the sick structure and the susceptibility to a disease. The processes, connected with the population's reproduction fecundity and the birth number play a great part in the health formation of different populations. Human health is a derivative of a gene pool of a certain population and a function of its social development at the same time from the ecological point of view. The law of the quantitative and qualitative sides of population's development is the basis of socio-ecological health concept.