Human Biological Adaptability

Human Biological Adaptability
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ability to rapidly adapt to varying
environmental conditions
 made
it possible for us to survive in most
regions of the world
most other species are restricted to one
or relatively few environments
 humans normally respond to
environmental stresses in four ways (first
3- biological, last one- cultural):
genetic change
 individuals inherit advantageous trait(s)
more likely to survive longer and pass on
genes to the next generation
ability to produce sweat for cooling our
bodies in hot environments
sickle-cell trait among the people of
Central Africa
A Mutation Story (4:50)
developmental adjustment
occurs in childhood and typically results in
anatomical and/or physiological changes
that are mostly irreversible in adulthood
○ have a high degree of physiological
can be physically molded by our environment
during the growing process
result from both natural environmental
pressures and cultural practices
the now illegal custom in China of tightly wrapping or binding the feet of
young girls
in China today the surgical breaking of the two lower leg bones in both legs
and then using adjustable metal braces to progressively extend the length
in the late 19th century tight corsets worn by girls when
their bodies were still growing (a 19 inch circumference
was the ideal)
customary for middle and upper class parents to have the teeth of their
children straightened with retainers and braces
3. acclimatization
forms of adjustment to environmental stresses
that are usually reversible
acquire dark skin tans during the summer
months and lose them during the winter
difference in pressure experienced in
mountains, flying, diving, can usually be
cancelled out by yawning, swallowing, or
chewing gum
4. Cultural Practices and Technology
over the last half million years at least, we
invented technological aids that allowed us
to occupy new environments without having
to first evolve biological adaptations to them
○ houses, clothing, and fire
Specific Human Adaptations
Climate Extremes
 have
unusually efficient internal
temperature regulating systems that
automatically maintain stable core body
 Bergmann's Rule
the more cells an animal has, the more heat it
will produce
 larger animals usually have a smaller surface
area relative to their body mass
Negative correlation between environmental temperature
and body mass in warm blooded animals
 the length of appendages also has
an effect on the amount of heat lost
to the surrounding environment
 members of the Masai tribe of East Africa
are normally tall and have slender bodies
with long limbs that assist in the loss of
body heat
 in cold environments, a stocky body with
short appendages would be more efficient
at maintaining body heat
High Altitude
 the
lower air pressure makes it more difficult for oxygen
to enter our vascular systems
populations are those
whose ancestors have lived at high
altitudes for thousands of years
 results
in some populations being
genetically more suited to the stresses at
high altitude, may…
 produce more hemoglobin
 increase their lung expansion
 breathe faster in order to take in more
 have broader arteries and capillaries
Skin Color Adaptation
 skin
color is due primarily to the presence of
a pigment called melanin
acts as a protective biological shield against
ultraviolet radiation
 ~90% of vitamin D is synthesized in their skin
and the kidneys with the help of UV radiation
 skin's ability to tan in summertime is an
acclimatization to this seasonal change
some Northwest Europeans have substantially lost the
ability to tan as a result of relaxed natural selection
 nature has selected for people with darker skin in
tropical latitudes
Nina Jablonski breaks the illusion of skin color (14:46)
Nutritional Adaptation
 some
people live well on daily diets that would
be at a starvation level for others
 adapting to local nutritional opportunities has
led to the evolution of related genetic
differences among the populations of the world
 the best documented differences in nutritional
adaptation relates to milk sugar, or lactose
the gene that codes lactase is on chromosome 2.
lactose intolerance is at its highest frequency in some
parts of Africa, East Asia, and among Native
northern Europeans generally have the lowest
frequency of this “dietary problem”
 Evolutionary
Significance of Lactose
ability of people in Europe and some other areas of
the world to continue producing lactase as adults is
very likely a relatively recent evolutionary
prior to the domestication of cattle, sheep, goats, and
horses after about 9000 years ago, milk was most
likely only consumed by babies and very young
dairy products such as cow's milk, yogurt, and
cheese did not exist
When nutrient rich nonhuman milk became widely
available in socities, the rare genetic variations that
allowed some adults to easily digest lactose were
selected for and this trait became more common
natural selection shifted to favor lactose tolerant people
European Americans
Latinos (Hispanic Americans)
African Americans
Native Americans
Asian Americans
Southern Sudan (cattle herders)
Ibo and Yoruba (Nigeria)
Australia (Aborigines)
2-19 %
52 %
70-77 %
95 %
95-100 %
83 %
12 %
15 %
18 %
28 %
32 %
37 %
88 %
79 %
17 %
99 %
90 %
99 %
85 %
 Adapting
to Alcohol
likely that natural selection is largely responsible for population
differences in the ability of humans to quickly metabolize
alcohol in beverages
metabolizing alcohol eliminates its toxicity and removes it from
the blood so that it won't cause cell and organ destruction
frequencies of the genes coding for the enzymes involved in this
protective process vary significantly from population to
beer and wine consumption have been common in Europe and
the Near East for 5-6 thousand years
many people in these same populations now have the genetic makeup that
gives them a relatively high tolerance of alcohol
in contrast, alcohol tolerance is unusual among Native Americans
with few exceptions, they have only had alcohol based beverages since the
arrival of Europeans, a few hundred years ago
 it is not surprising that alcoholism and alcohol related problems such
as cirrhosis of the liver are at comparatively high rates among many
Native American groups.

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