| Themes > Science > Life Sciences > General Biology > Physiology > The Reproductive System > Landmarks |
The stages of life are noted by the acquisition of social, physical, and mental skills. Other signs of maturation include tattoos, body piercing, motorcycles, and backward-turned baseball caps. Infancy and Childhood Infancy lasts from birth until age two. Infant reflexes concern finding the nipple: suckling can occur minutes after birth, and the rooting reflex is a tactile clue for the infant to turn its head toward a touch. During the first year the infant passes through a series of developmental stages. Childhood begins at two and lasts until puberty. Physical growth is accompanied by increasing development of motor and language skills. Play, make-believe, and increases in memory and attention span also occur. Adolescence and Adulthood Growth accelerates during puberty. Boys increase in height by 3-5 inches per year, girls 2-4 inches. The heart doubles in size, and hormones stimulate sexual maturity. Growth ends during the end of adolescence, and aging starts during the late twenties. Life expectancy (47 and 50 years for males and females in 1900; 74 and 81 in 1996) has increased. |
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