1. Why does hair get darker after infancy and turn white in old age?
A child's developing hair becomes impregnated by hundreds of thousands of pigment cells called melanocytes, which produce 2 types of pigments, eumelanin (which darkens the hair black or dark-brown), and phaeomelanin (resulting in either blond or ginger hair.)Hair darkens from birth onward as melanocytes intensify their activity up to about age 15, then stabilize until just after age 30. After that, the pigment production rate slows down and hair starts to turn grey until the rate ceases in old age and thus the hair turns white, the natural color of its proteins.
2. Why do we yawn, and why is yawning contagious?
People yawn when there is a decrease in the oxygen level in the lungs and a resulting accumulation of carbon dioxide in the blood. This is usually an indication of sleepiness or hunger. Because this is a sort of nervous reflex, it can also happen by imitation.3. Why do Africans have such curly hair?
Evolution has equipped the people native to central Africa, where the temperatures commonly reach 40 degrees Celsius, with an effective weapon against overheating of the scalp (and thus of the brain.) Cerebral tissue begins to degenerate above about 40 degrees, so the hair's insulating cushion of tight, wiry "curls" and the scalp's secretion of natural oils helps to keep temperatures below danger levels.4. Why do bean plants wrap their tendrils counterclockwise around their support poles?
Bean shoots grow towards the sun to enable the process of photosynthesis to occur. In the Northern Hemisphere, as the sun moves east to west through the sky, the bean plants follow its path and thus wrap themselves counterclockwise around support poles.Of course, this process is reversed in the southern hemisphere.
