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Chapter 12

AN101 Chapter Notes - Chapter 12: Vasodilation, Preterm Birth, Vasoconstriction

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Todd Ferretti

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Chapter 12- page 314-332
-Physical anthropologists use the approach of POPULATION GENETICS to interpret microevolutionary
patterns of human variation.
-POPULATION GENETICS—the study of the frequency of alleles, genotypes, and phenotypes in
populations from a microevolutionary perspective.
-attempts to identify the various factors that cause allele frequencies to change over time.
-a POPULATION is a group of interbreeding individuals that share a common GENE POOL. *population is
the group where people are most likely to find mates.
-In every generation, the genes (alleles) in a gene pool are mixed by recombination and then reunited
with their counterparts (located on paired chromosomes) through mating.
-factors that determine mate choice are GEOGRAPHICAL, ECOLOGICAL, and SOCIAL.
-BREEDING ISOLATES—populations that are clearly isolated geographically and/or socially from other
breeding groups. EX. (being stranded on a desert island)
**breeding isolates are a target of microevolutionary studies.
-geography plays a dominant role in producing these isolates by strictly determining the range of
available mates.
-once specific human populations have been identified, the next step is to ascertain what evolutionary
forces, if any, are operating on them.
-to determine whether evolution is taking place at a given locus, population geneticists measure allele
frequencies for specific traits and compare these observed frequencies with a set predicted by a
mathematical model called the HARDY-WEINBERG EQUILIBRIUM equation. –provides a tool to establish
whether allele frequencies in a population are indeed changing.
-HARDY-WEINBERG EQUILIBRIUM: the mathematical relationship expressing, under conditions in which
no evolution is occurring, the predicted distribution of alleles in populations; the central theorem of
population genetics.
--Factors that act to change allele frequencies, including:
1. New Variation (new alleles produced by mutation)
2. Redistributed Variation (gene flow, genetic drift)
3. Selection of ‘advantageous’ allele combinations that promote reproductive success (natural selection)
-today, biological anthropologists view human variation as the result of such evolutionary factors as
genetic drift, founder effect, gene flow, and adaptations to environmental conditions.
-numerous fluctuations in physical activity in temp, wind, solar radiation, humidity, etc. Happen daily.
-physical activity places STRESS on physiological mechanisms.
-STRESS—in a physiological context, any factor that acts to disrupt homeostasis; more precisely, the
body’s response to any factor that threatens its ability to maintain homeostasis.
*the body must accommodate all these changes by compensating in some manner to maintain internal
constancy, or HOMEOSTASIS, and all life forms have evolved physiological mechanisms that, within
limits, achieve this goal.
-HOMEOSTASIS—a condition of balance, or stability, within a biological system, maintained by the
interaction of physiological mechanisms that compensate for changes (external and internal)
-adaptation refers to long-term evolutionary (genetic) changes that characterize all individuals within a
population or species.
-ACCLIMATIZATION—another kind of physiological response to environmental conditions, it can be short
term, long term, or permanent. * partially influenced by genes, some can be affected by the duration
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and severity of the exposure, technological buffers (shelter or clothing) and individual behaviour,
weight, and overall body size.
-Simplest type of Acclimatization is a temporary and rapid adjustment to an environmental change. EX.
-DEVELOPMENTAL ACCLIMATIZATION—is irreversible and results from exposure to an environmental
change during growth and development.
Solar Radiation and Skin Colour
-skin colour is a commonly cited example of adaptation through natural selection in humans.
-skin colour is mostly influenced by the pigment MELANIN, a granular substance produced by specialized
cells (MELANOCYTES) found in the epidermis. All humans have approx the same number of melanocytes,
amount and size of melanin granules that vary.
-Melanin acts as a built in sun-screen by absorbing potentially dangerous UV rays. *melanin protects us
from over exposure to UV radiation which can cause genetic mutations in skin cells. (lead to cancer)
-Tanning-result of temporarily increased melanin production.
-ABINOS-carry a genetic mutation that prevents their melanocytes from producing melanin.
-women tend not to tan as deeply as men.
Dark Skin
-Natural selection has favoured dark skin in areas nearest to the equator, where the sun’s rays are most
direct and thus where exposure to UV light is most intense.
-In considering the cancer-causing effects of UV radiation from an evolutionary perspective:
1. Early hominins lived in the tropics, where solar radiation is more intense than in temperature areas in
the N & S.
2. Unlike modern city dwellers, early hominins spent their days outdoors.
3. Early hominins didn’t wear clothing to protect them from the sun.
-Given these conditions, UV radiation was probably a powerful agent selecting for high levels of melanin
production in early humans.
-JABLONSKI , JABLONSKI & CHAPLIN—focuses on the role of UV radiation in the degradation of a B
vitamin called folate. FOLATE isn’t stored in the body and therefore must be replenished through dietary
sources. Folate deficiencies in preggers women are associated with numerous complications, like
maternal death and NEURAL TUBE DEFECTS—the anatomical structure that develops to form the brain
and spinal cord in early embryonic development. *^pain, infection, paralysis, and even death.
-neural tube defects can dramatically reduce the reproductive success of affected individuals.
-some studies have shown that UV radiation rapidly depletes folate serum levels in fair skinned
-J & C—suggest that earliest hominins may have had light body skin covered in dark hair, like chimps and
gorillas. But as loss of body hair occurred, dark skin evolved rather quickly as a protective response to
the damaging effects of UV radiation on folate.
Lighter Skin
-as hominins migrated out of Africa into Asia and Europe, they faced new selective pressures.
-europe =cold temps, cloudly skies, winter means few hours of daylight, solar radiation very indirect,
people wore animal skins and other types of clothing to keep warm which blocked the suns ray.
-the advantages of deeply pigmented skin in the tropics no longer applies, and selection for melanin
production may have been relaxed.
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