Biology · Organisms and Populations · NEET
Heat leaves the body through the body surface. Long ears and long limbs add a lot of extra surface area. More surface means more heat lost. In a cold place an animal must keep heat inside, so evolution favours short ears and short limbs. This lowers the surface area for a given body volume, so less body heat escapes and the animal stays warm.
It decreases the exposed surface area relative to body size. Shorter ears and limbs = smaller surface area to volume ratio = less heat loss. Desert animals do the opposite: big ears (like the fennec fox or desert hare) give more surface area to throw off heat and stay cool. So cold = small parts, hot = large parts.
No. Bergmann's Rule is about total body SIZE — cold-climate animals tend to be larger (a big body has less surface area per unit volume, so it loses heat slowly). Allen's Rule is about the SHAPE of the ends — shorter ears, limbs and tail. Both aim to reduce heat loss in the cold, but one changes size and the other changes the length of body extensions.
The detailed 'adaptations' section, including Allen's Rule, was trimmed from the rationalised NCERT reprint and is treated as out of the NEET 2026 core syllabus. But it appeared as a real question in NEET 2021, and Bergmann/Allen logic is common general biology. Learn the surface-area idea — it is quick to grasp and protects you if a similar match-the-column question appears.
A thermal adaptation is a fixed body feature that helps an animal cope with temperature — like short ears (Allen's Rule), thick fur, or a blubber fat layer in seals and whales. Regulation is an active process (like sweating or shivering) that keeps body temperature constant. Adaptation is the built-in structure; regulation is the ongoing action.
Match List I with List II: List I: A. Allen's Rule B. Physiological adaptation C. Behavioural adaptation D. Biochemical adaptation List II: I. Kangaroo rat II. Desert lizard III. Marine fish at depth IV. Polar seal Choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mammals in cold climates have shorter ears and limbs to reduce surface area and lose less body heat.
The polar seal and Arctic fox have short ears and short limbs; desert animals like the fennec fox have large ears to lose heat.
Allen's Rule is about shorter body extensions (ears, limbs); Bergmann's Rule is about larger overall body size. Both reduce heat loss in cold climates.
Heat escapes through the body surface. Smaller surface area for the same body volume means fewer places for heat to leave, so the animal stays warmer.
It is out of the rationalised NCERT core, but it appeared in NEET 2021 and the surface-area logic is easy and safe to learn for match-the-column questions.
