Moalem's Survival Of The Sickest Practice Test

The main idea is that skull shape can adapt to climate to help regulate body heat. The head is a site where heat can be gained or lost, and the skull’s size, shape, and features influence how efficiently heat is exchanged with the environment. In hot climates, natural selection can favor skull shapes that promote heat dissipation, increasing surface area or pathways for cooling. In cold climates, a more compact skull with less surface area helps conserve heat. This pattern fits with how cranial features vary across populations as an adaptive response to temperature and humidity demands, including aspects like how the nasal passages humidify and warm inspired air. So describing skull shape as evolving to facilitate heat retention or release depending on climate captures the thermoregulatory role of morphology. The other options treat skull shape as random, purely cosmetic, or without evolutionary significance, which doesn’t reflect the observed link between climate and cranial form.