Development begins at conception when a sperm from the father fertilizes an egg from the mother, creating a new life. The resulting zygote grows into an embryo and then a fetus.
Babies are born prepared with reflexes and cognitive skills that contribute to their survival and growth.
Piaget’s stage model of cognitive development proposes that children learn through assimilation and accommodation and that cognitive development follows specific sequential stages: sensorimotor, preoperational, concrete operational, and formal operational.
An important part of development is the attainment of social skills, including the formation of the self-concept and attachment.
Adolescence involves rapid physical changes, including puberty, as well as continued cognitive changes. Moral development continues in adolescence. In Western cultures, adolescence blends into emerging adulthood, the period from age 18 until the mid-20s.
Muscle strength, reaction time, cardiac output, and sensory abilities begin to slowly decline in early and middle adulthood. Fertility, particularly for women, also decreases, and women eventually experience menopause.
Most older adults maintain an active lifestyle — remaining as happy as they were when they were younger, or happier — and increasingly value their social connections with family and friends.
Although older adults have slower cognitive processing overall (fluid intelligence), their experience in the form of crystallized intelligence, or existing knowledge about the world and the ability to use it, is maintained and even strengthened during aging. A portion of the elderly suffer from age-related brain diseases, such as dementia and Alzheimer’s disease.