Human development life span is a process that begins between conception and birth of a child and proceeds till old age. The process involves personal growth both mentally and physically, however, the rate of growth differs from one individual to the other such that some children or adolescents will be more physically developed (height and muscles) than others of the same age. Despite genetic and environmental factors having an influence on physical development, some concepts including cephalocaudal, proximodistal, and Orthogenetic principles explain the pattern of human growth and development. Indeed, the physical posture of an individual becomes more balanced as he/she develops from infancy to adulthood.
The physical body of an individual during infancy is largely disproportional. According to the cephalocaudal principle, the head occupies 50% of the body size of a two-month fetus but as physical development occurs, the body becomes more proportional with the head accounting for 12% of body length and 2% of body weight while the legs accounting for 50% of body length in an adult person (Siegleman and Rider, 2008, p.128). This concept views physical growth and development to progress from the head downwards, with the trunk growing fastest during the first year after birth and the legs growing fastest thereafter. Siegelman and Rider (2008, p. 128) also describe the physical growth in terms of proximodistal concept where the internal organs and chest are said to grow faster during the early period of infancy and then the growth spreads to the extremities (arms) thereafter. The third concept, Orthogenetic, provides a different view with the body being seen to initially grow universally with no differentiation and then thereafter the body organs become differentiated and organized as the developmental process progresses.
Given that physical growth is influenced by the brain and endocrine system, any interference of the neural system or secretion of body hormones will interfere with the physical developmental process. The reasons why different children will exhibit different physical developmental patterns will therefore not only be due to genetic and environmental factors but also to the different hormonal influences, for instance, where the pituitary glands are unable to secrete adequate growth and activating hormones, an individual may experience retarded growth, while where the adrenal androgens are insufficient, the bones and muscles may not develop effectively (Siegleman and Rider, 2008, p.125).
These concepts of human physical development are important since they give an understanding of human growth as an organized sequence that needs to be followed throughout the life of an individual. In addition to enhancing knowledge on developmental patterns from conception to adulthood, they give an important illustration of the reasons behind the unequal rate of physical development between individuals. For instance, an infant has the most rapid growth rate and highly sensitive reflexes (Siegleman and Rider, 2008, p.131); children of two and above years have steady growth and their physical behavior more or less controllable while their physical health may be enhanced not only by nutrition but also physical activity; the adolescents’ physical growth spurt due to increased hormonal secretion and setting in of maturation, where the body takes shape (for both girls and boys) and sexual maturation is reached.
With the understanding of these concepts, a psychologist will be in a better position to establish the causes of certain developmental deficiencies in some individuals and apply corrective measures early enough. Moreover, the psychologist will be able to provide convincing explanations and counseling to individuals who may be psychologically affected by their alleged physical difference, which may or may not necessarily be a developmental problem but a differing growth rate from others.
References
Sigelman, C. K. and Rider, E. A. (2008). Life-Span Human Development. Sixth Edition. NY: Cengage Learning.