The density of the wool of mammals in the middle lane changes throughout the year, molting occurs. Explain what kind of variability

The density of the wool of mammals in the middle lane changes throughout the year, molting occurs. Explain what kind of variability is observed in mammals and what determines the manifestation of this trait.

1) there is a manifestation of modification (non-hereditary, definite, phenotypic) variability;
2) the manifestation of this feature is determined by seasonal changes in temperature and day length.

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