Human stages of growth and development are differentiated by age and key stages of scientifically supported psychomotor development. Psychomotor development is progress in mental and motor skill activity. The process of growing and developing begins on the cellular level even before conception in the womb and continues throughout life until death. The scientific community divides human growth into stages according to age and assesses psychomotor development as a human develops motor skills and reaches cognitive milestones. Most human stages of growth and development occur in infancy, childhood and adolescence.
The period of time between birth and adolescence is commonly divided into four growth stages: infancy, childhood, juvenile and adolescence. According to the American Academy of Pediatrics' website, every stage of development has certain milestones. At 1 month of age, for instance, a baby's hearing is fully mature, and infants of this stage often respond to loud sounds and familiar voices. A cognitive milestone for a 1-year-old is being able to find missing objects after watching someone hide them. Although every child does not stay within the same time frame in development, parents should note delays in psychomotor development and bring them to the attention of a paediatrician.
A baby is considered an infant from birth through the first year of life. During this first year, babies develop skills that will be lifelong resources. Paediatricians look for specific markers of growth and development during this time. Learning how to control the head, move by crawling and sit are called gross motor skills. Using the thumb and finger to pick up pieces of food and hold a pacifier are called fine motor skills. Sensory skills are measured by observing a baby's ability to see, hear, taste, touch and smell. Language skills are evident the first year of life when a baby makes sounds, learns some basic words and responds to the spoken word. Finally, social skills include how a baby interacts with family and peers.
After age 1 year, a child's physical growth slows down considerably. The toddler years are more mobile and exploratory. Middle childhood occurs about age 6 years, and children have a better sense of right and wrong then. They also tend to become more independent as they begin dressing themselves and spend more time at school and with friends. Cognitive changes include rapid mental growth with a greater ability to talk situations through and focus on the environment around them instead of being self-centered.
As children approach the ages of 9 and 10 years, they become more independent and might start noticing the physical changes of puberty. A major growth spurt can occur at this time as the body begins sexual development. This also can be a time of stress for children as peer pressure takes its toll. Body image along with emotional changes often cause children to feel less confident. Juveniles also start preparing for middle school by taking on more academic responsibilities and focusing on goal-setting and accomplishment.
From ages 12 to 18 years, children experience distinct mental and physical changes. According to the National Institutes of Health (NIH), the beginning of a girl's menstrual cycle typically occurs 2 years after the onset of puberty. The NIH reports that boys do not begin puberty with a distinct marker and tend to mature with adult genitalia about age 16 or 17 years. During this time of physical change, adolescents may become more self-centered. In middle to late adolescence, teenagers are often characterised as becoming more comfortable with their body sexually and ready to have romantic friendships. Adolescent behaviour often includes the teenagers' need to pull away from parents and authority figures to establish their own self-identity and make decisions on their own.
Adulthood is often noted when a person is considered chronologically, legally and behaviorally ready to hold responsibilities such as operating a motor vehicle, voting, taking the vows of marriage, entering into a contract and serving in the armed forces. The process of becoming mature does not end with adolescence but continues throughout adulthood as psychological, safety and self-actualisation needs are met. Adulthood is often divided into three categories: young adulthood, middle age and old age.