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Bogin (1997) - Evolutionary Hypotheses for Human Childhood.docx

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Health Studies
R Song

Evolutionary Hypotheses for Human Childhood Bogin, B (1997) th - Many historical sources from Egyptian times to the 19 century, including Wordsworth in the poem in the text, mention that “childhood” occupies the first 6-7 years of life. - Evolutionary success is traditionally measured in terms of the number of offspring that survive and reproduce. - Childhood (in this essay) is defined as the period following infancy, when the youngster is weaned from nursing but still depends on older people for feeding and protection. - Several biological and behavioural characteristics of the youngster necessitate this dependency of childhood. - In terms of feeding there are three major biological factors: 1. Children continue the rapid brain growth experienced by infants and need a diet dense in energy and protein to support this brain growth. 2. Children possess deciduous teeth, with thin enamel and shallow roots, and cannot process the adult-type diet. 3. Children have relatively small body size, and hence a small digestive system, which limits the total food intake, furthering the requirement for nutrient-dense foods. - Human childhood period spans the time from about 3-7 years of age. - Childhood is likely to be a new life cycle stage that was evolved de novo into hominid life history. - The opposite and older views of childhood are is that childhood evolved by altering the developmental timing of the pre-existing life stages of our primate ancestors. - The two most popular hypotheses in this regard invoke either neoteny or hypermorphosis as the primary agent of human evolution. - Neoteny may be thought of as a slowing down of the rate of development. Neoteny produces an adult descendent that retains many immature characteristics of its ancestor. - Hypermorphosis is an extension of the growth and development period of the descendant beyond that of the ancestor. Hypermorphosis produces a descendant with features that are hypermature compared with the ancestor. - This essay argues that neither neoteny nor hypermorphosis can unravel the paradox of human evolution. Human Ontogeny and Heterochrony (65) - Ontogeny refers to the process of growth, development, and maturation of the individual organism from conception to death. - During hominid evolution the form and function of our ancestor’s structural and regulatory DNA was reworked to produce the genetic basis for the ontogeny of the human species. - S.J. Gould handily summarizes the mechanisms for biological change over time by stating, “Evolution occurs when ontogeny is altered in one of two ways: when new characters are introduced at any stage of development with varying effects upon subsequent stages, or when characters already present undergo changes in developmental timing. Together, these two processes exhaust the formal content of phyletic c
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