Human growth is one of the most phenomenal occurrences in the world, yet it is taken for granted. With animals, it begins with the fusion of a sperm and egg, leading to the body's growth and eventually its deterioration. Plants, animals and other creatures grow in different phases. Some things live only hours or days, while others, such as trees, live thousands of years.
Although too small for the eye to see, one of the most critical stages of human development occurs at the very beginning. When an egg and sperm combine to form a zygote, one of the key events that takes place is meiosis, which is responsible for genetic variation. The zygote will divide and grow, ultimately producing an infant.
Human infancy is a very critical and vulnerable time. Babies completely depend upon their parents for protection, food and development. According to Erik Erikson, this stage develops trust vs. mistrust -- a key to people's future outlook on life. During the infancy stage, much emphasis is placed upon visual and contact learning.
Childhood & Adolescence
Childhood provides knowledge that becomes critical during the later stages in life. This includes knowledge of walking, talking and emotions. As children age towards adolescence, they learn many social skills through interaction with peers. Adolescence starts the first period of development where identity development takes place, giving individuals a sense of uniqueness. This period also causes critical changes in the body, as hormone levels change and adolescents go through pubescent changes, allowing them to become reproductively fertile.
During the late teens and early 20s, women are most receptive to conceiving children. As women age, their eggs become fewer, limiting their ability to reproduce. Men, on the other hand, always produce sperm, allowing them to produce children into old age. The adult stages of life emotionally revolve around love and reproduction, as well as financial accomplishment. Scientifically, ageing occurs through the process of telomere shortening, where segments of DNA gradually degrade, causing the body to age.