This process is called hardening. Scientists believe several events cause hardening. Hardening may result from a decrease in the water content and an increase in the sugar content of the plant. This keeps the plant from freezing. Animals acclimatize in many ways.
Sheep grow very thick wool in cold, damp climates.
Most human beings become short of breath and tire easily when they move to higher altitudes. After the body adjusts to the new altitude, the symptoms disappear. Lawrence C. Wit, Ph.D., Professor of Zoology, Auburn University. How to cite this article.