| Abstract: |
In order to learn more about the evolutionary developments of human growth it is argued that a life history approach needs to be undertaken. Life history theory is an attempt to identify tradeoff problems in reproductive investment so as to maximize the contribution of genetic material to the following generation. This is done by studying the stages of human development which are infancy, childhood, juvenile, adolescence, and adulthood. Childhood and adolescence are of particular interest since these are unique to the evolution of the human species. In this articles, Bogin also advocates the need for a biocultural perspective in which the biological process is considered to be influenced not only by the environment but also by the social and cultural variables that exist. The patterns of human growth after birth are characterized by five stages. Infancy, is the period from which all nutritional also physical needs too solely provided by the mother via lactation. It ends when the child is weaned from the breast which is typically sometime after the two years of life in traditional societies and approximately one year in urban industrial populations. Childhood begins after weaning and ends when the growth of the brain (in weight) is complete which is around seven years of age. There are seven reasons discussed as to why human beings have childhood and its seems that except for the theories for an extended period for brain development, they are actually direct reproductive adaptations for the parents with indirect benefits to the child. The Juveniles stage is defined as a prepubertal in which the child is no longer dependent on the mother for survival. It ends at the onset of pubertal which is highly variable but typically around 10-13 years of age. Adolescence begins with puberty and ends with the attainment of adult stature and full reproductive maturity which includes socioeconomic, and psychobehavioral attributes that appear around the ages of 19-25. This stage is marked by a rapid acceleration in growth of the skeleton as well and has been suggested to be a "catch up" period to compensate for time "lost" to learning in early life. This has methodological problems however as growth spurts are not needed for reaching adult height or fertility. Further, while the growth spurt is largely responsible for sexual dimorphism in height, it does not explain it timing. In other words, adolescence has it own intrinsic evolutionary value as it enhances survival and reproductive success. It is not just the by-product of slow prepubertal development. Another point of interest is that pelvic size is not correlated with these growth spurts but follow there own unique slow growth cycle which is not complete till up to ten years after first menarche. What determines adolescence also has cultural variables as well for it is important to remember that the human success story is also based, in part, due to the experience and knowledge gained during these stages. When childhood and adolescence evolved in human evolution is also questioned. These ideas stem from the concept that reproductive adaptations for the parents are greater than in children. It has been suggested that the archaeological evidence for stone tool usage may be interpreted as an adaptation strategy to feed children. This may justify an expansion of the childhood period to provide the high quality foods needed for the rapid brain growth in humans after birth as opposed the slow rate of growth in other primates. Also, juvenile growth has been suggested to provide a means of cultural education and as a babysitting mechanism to free adults to that they can provide their needs more easily and decrease the time between births.
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