HLTC23H3 Chapter Notes -Deciduous Teeth, Ontogeny, Heterochrony

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Published on 10 Aug 2012
School
UTSC
Department
Health Studies
Course
HLTC23H3
Professor
Evolutionary Hypotheses for Human Childhood Bogin, B (1997)
- Many historical sources from Egyptian times to the 19th 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 change.”
- Gould contends that it is the second process that accounts for human evolution, called heterochrony changes in the
relative time of appearance and rate of development for characters already present in ancestors.
- There are many types of heterochronic processes, but only neoteny accounts for human evolution. Neoteny is defined
as (by Gould’s book) “paedomorphosis (retention of formally juvenile characters by adult descendents) produced by
retardation of somatic development.
Neoteny and Human Evolution (66)
- That humans of all ages are essentially child-like morphology, behaviour, and cognitive potential is the essence of the
concept of neoteny.
- The idea that neoteny is the primary process for humanization was first formalized scientifically by Louis Bolk in 1926.
- Gould believes that if humans evolved by neoteny...then we are, in a more metaphorical sense, permanent children.
- A prominent social anthropologist claims that human evolution via neoteny allows for the development of human
culture, especially religion.
Hypermorphosis and Human Evolution (67)
- The proposition that adult humans are permanent children is not accepted by all scholars.
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Document Summary

Evolutionary hypotheses for human childhood bogin, b (1997) Many historical sources from egyptian times to the 19th 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: Children continue the rapid brain growth experienced by infants and need a diet dense in energy and protein to support this brain growth. Children possess deciduous teeth, with thin enamel and shallow roots, and cannot process the adult-type diet.

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