  We have modified the sexual Penna model by introducing the fluctuating
environment and fluctuations representing physiological functions of
individuals. Additionally, we have introduced the mother care corresponding to
the protection against the deleterious influence of the environment, the
learning capacity of individuals corresponding to their immunity and adaptation
to the environment fluctuations and the other risk factors appearing at
puberty. Each of the above mentioned elements influences mainly the survival of
newborns and young individuals while genetic defects accumulated in the genomes
increase the noise of individuals and were responsible for higher mortality of
older individuals. All these modifications enable precise fitting the age
structure of the simulated populations to the age distributions of human
populations.
