Bergman’s rule : Stockier body type in colder climates.Body size and shape play effective role-in conservation of heat and production of heat. The body size in colder regions increases because it results in greater mass in comparison to skin area, meaning less surface area. this large body produces more metabolic heat and due to less surface area the heat is conserved. Thus animals including man having cold adaptation tend to be larger in size .
Allen’s rule: Besides body size, cold adapted human beings also have relatively shorter extremities and limbs. Shorter extremities reduce body surface area; hence more heat is conserved in comparison to people having longer extremities.
1) Shorter limbs in colder climates—low surface area leads to body mass retaining heat
2) Longer limbs in warmer climates—high surface area: body mass loses heat
Glogger’s Rule: People living in hot & damp places tend to have very dark skin
Normal Hemoglobin, Abnormal hemoglobin variants: Hbs and HbE, Balanced polymorphisms
- Greenland Inuit with low European mixing, living in villages on the coast of Baffin Bay.
- Eskimos living in Tundra region of Canada and North pole have bulky body due to presence of subcutaneous fat.
In the Australian aborigines, the body temperature falls much lower so that they are prone to frostbite and their limbs become numb during night. They often burn their extremities because they sleep nude around campfire.
Non genetic factors
Cultural factors- Habit and habitat
- Eskimos use the clothing from Caribou’s fur which keeps them warm.
- North East Siberians such as Inuit live in ‘Igloos’ where air pockets trapped in snow act as insulators and keep the inside temperature more than outside temperature.