Human Adaptation to Natural Environmental Stressors 301Humans possess two additional biological mecha-
nisms through which they can adapt. The first of these,
developmental adaptation, also produces permanent phe-
notypic variation as the environment shapes the expression
of the genes each individual possesses. The extended pe-
riod of growth and development characteristic of humans
allows for a prolonged time period during which the envi-
ronment can exert its effects on the developing organism.
The anthropological focus on growth and develop-
ment has a long history dating back to the work of Franz
Boas, the founder of American four-field anthropology.
Boas is credited with discovering the features of the hu-
man growth curve (Figure 13.1). He demonstrated that
the rate of human growth varies in typical patterns until
adulthood, when physical growth ceases. Humans expe-
rience a period of very rapid growth after birth through
infancy, followed by a gradually slower rate of growth dur-
ing childhood. At adolescence, the rate of growth increases
again during the adolescent growth spurt.
In addition to describing the long-term pattern of hu-
man growth, anthropologists have also demonstrated that
within periods of growth, the actual growth process pro-
ceeds as a series of alternating bursts and relative quiet.^2While humans possess a number of exquisite biological
mechanisms through which they have adapted to the nat-
ural environment, these mechanisms can fall terribly short
in today’s globalizing world. Before turning to the chal-
lenges we face from the dramatic changes we have made
in our environment today, we will explore the biological
mechanisms humans have used over millennia to adapt to
three naturally occurring environmental extremes: high
altitude, cold, and heat.Human Adaptation to
Natural Environmental
Stressors
Studies of human adaptation traditionally focus on the
capacity of humans to adapt or adjust to their environ-
ment through biological and/or cultural mechanisms.
Darwin’s theory of natural selection accounts for dis-
crete genetic changes built into the allele frequencies of
populations, such as the various adaptations to malaria
that we have examined. It also provides the mechanism
for understanding that adaptations, evident in popula-
tion variation of continuous phenotypic traits, depend
upon multiple interacting genes. Even when the genetic
bases to these adaptations (such as skin color or body
build) are not precisely known, scientists can study
them through comparative measurement of the associ-
ated phenotypic variation.Kilograms706050403020100
Birth1 2 3 4 5 6 7 8 9 1011121314151617 18
Age in yearsWeight gain (kilograms per year)14
13
12
11
10
9 8 7 6 5 4 3 2 1 0Birth 123456789101112131415161718
Age in yearsGirlsGirlsBoysBoysFigure 13.1 Franz Boas defined the features of the human growth curve. The graph on the left
depicts distance, or the amount of growth attained over time, while the graph on the right shows the
velocity, or rate of growth over time. These charts are widely used throughout the globe to determine
the health status of children.(^2) Lampl, M., Velhuis, J. D., & Johnson, M. L. (1992). Saltation and stasis:
A model of human growth. Science 258 (5083), 801–803.
developmental adaptation A permanent phenotypic varia-
tion derived from interaction between genes and the environ-
ment during the period of growth and development.
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