It takes time for everything, including what happens in the human body. The following are some little-known facts about the human body and time.
◊ Fingerprints form six to eight weeks before birth.
◊ Fingernails grow about four times faster than toe-nails – about 0.5 mm per week.
◊ If a child below the age of 12 has their finger tips and nails severed above the first crease of the first joint, they can regenerate. Regeneration takes about eleven weeks. Adults do not have this ability.
◊ In the foetal brain, nerve cells develop at an average rate of more than 250,000 per minute. At birth, a child's brain contains close to a trillion nerve cells. After birth, this rate of neuron growth slows down dramatically.
◊ Taste buds are among the earliest sense organs to appear. By the third trimester of pregnancy, foetal taste buds are responsive to chemicals in the amniotic fluid. The life-span of a taste bud cell is about 10.5 days.
◊ On average, nerve regeneration takes four to six weeks.
◊ Gums are renewed every one to two weeks.
◊ Eyelashes, which are more plentiful on the upper eyelid than on the lower eyelid, are shed continuously. Each of the more than 200 hairs per eye lasts from three to five months.
◊ The vibrations in the air constitute sound waves. The higher the pitch, the greater the frequency or cycles per second. Adults can detect sound waves that have a frequency between about 16 and about 20,000 cycles per second. Yet they hear best at frequencies ranging from about 1000 to 2000 cycles per second.
◊ Children hear higher-pitched notes better than adults. After puberty, this sensitivity declines at the same time as the voice deepens. Thus, our ears are best adapted to the pitch or sound frequencies of human conversation.
◊ The ability of the brain to detect the location of a sound depends on the differences in the time of the arrival of the sound to the two ears. We can detect the source of a sound even if it arrives in one ear a hundredth of a second before it gets to the other.
◊ The body loses water through the skin (from simple diffusion) at the rate of half a litre per day. The body loses about the same amount of water each day from the lungs in breath. Each breath lasts about five seconds.
Stephen Juan, PhD is an anthropologist at the University of Sydney, Australia.
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