Surface-area-to-volume ratio
The surface-area-to-volume ratio or surface-to-volume ratio is the ratio between surface area and volume of an object or collection of objects.
Cells lining the small intestine increase the surface area over which they can absorb nutrients with a carpet of tuftlike microvilli.
Allen's rule is an ecogeographical rule formulated by Joel Asaph Allen in 1877, broadly stating that animals adapted to cold climates have shorter and thicker limbs and bodily appendages than animals adapted to warm climates. More specifically, it states that the body surface-area-to-volume ratio for homeothermic animals varies with the average temperature of the habitat to which they are adapted.
Eskimo Group by photographer William Dinwiddie (1894)