human physical adaptation

7/29/2019 Human Physical Adaptation

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Human Physical AdaptationHuman Physical Adaptation

Social Science ISocial Science ISecond Semester, SY 2010Second Semester, SY 2010--20112011

UP VisayasUP Visayas


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AdaptationAdaptation- long-term (evolutionary) changes that

characterize all individuals within a populationor species

- functional response to environmentalconditions in populations and individuals


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Adaptation at Various LevelsAdaptation at Various Levels1.1. Genetic adaptationGenetic adaptation the evolution of

advantageous characteristics2.2. Developmental adaptationDevelopmental adaptation the acquiring

grows up in a particular environment

3.3. LongLong--term acclimatizationterm acclimatization acquired over

the years but reversible underenvironmental change


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Adaptation at Various LevelsAdaptation at Various Levels4.4. Seasonal acclimatizationSeasonal acclimatization reverses itself

during the annual cycleExample: tanning

5. Short5. Short--term acclimatizationterm acclimatization manifest indaily or irregular responses to conditions


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Skin Color AdaptationSkin Color Adaptation

Skin color : hemoglobin, carotene, and melanin

Melanin chief skin pigment

- a granular substance produced by specializedcells in the epidermis called melanocytes.


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Melanin absorbs ultraviolet rays present in

sunlight; provides protection fromoverexposure to ultraviolet radiation which can

Adaptive response:

Exposure to sunlight triggers increased

melanin production


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Natural selection appears to favor dark skin in

areas where exposure to ultraviolet light ispronounced.

Note: cultural adaptation is also important.


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Another important note:

After hundreds of years, Europeans in thetropics are still light and African Americans in

.years, however, American Indians in thetropics are slightly darker than those in North

America.


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Vitamin D

- Necessary for normal bone growth andmineralization

- yn es ze n e o y par y as a resu o einteraction of ultraviolet radiation and asubstance similar to cholesterol


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Vitamin D Hypothesis

- selection of lighter skin in high latitude areas forvitamin D synthesis.Evidences:

a er eca es o e cen ury: r canAmerican inhabitants of US northern citiessuffered a higher incidence of rickets than whites

In Britain, dark-skinned East Indians and

Pakistanis show a higher incidenceof rickets


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Adapting to Climate ExtremesAdapting to Climate Extremes

- Mammals and birds have evolved complexmechanisms for increasing or reducing of body

temperature (homeothermy)


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HypothermiaHypothermia life threatening drop in core

body temperature to subnormal levels- Begins to occur when core body temperature

.Celsius)

Note: human body temperature

is 98.6 degrees Fahrenheit(37.0 degrees Celsius).


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HyperthermiaHyperthermia rising of body temperature to

fatal levels- Begins to occur when core body temperature

- . -4.17degrees Celsius) result in deterioration ofinternal organs, and death.


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Response to HeatResponse to Heat

- In humans, sweat glandssweat glands (approximately 1.6

million) are distributed throughout the skinmake possible the loss of heat at the body

-- Reduced amounts of body hairReduced amounts of body hair- enhances thecooling effects of sweating


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VasodilationVasodilation expansion of blood vessel

permitting blood flow to the skin.- Permits heat, carried by the blood from the

,skins surface to the surrounding air.

- An involuntary response to warm

temperatures, various drugs, and evenemotional states (e.g., blushing).


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Body Size and ProportionBody Size and Proportion

- In general, body size (weight) increases as

s ance rom e equa or ncreases


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Bergmanns Rule

- from German biologist Carl Bergmann

- concerns relationship of body mass or volume

o sur ace area: as mass ncreases, e re a veamount of surface area decreasesproportionately.


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Response to HeatResponse to HeatBergmanns Rule

: Volume increases twice as fast as the surface

area. Less surface area results in less heat beinglost from animals.


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Allens Rule

- from American biologist Joel Allen. Allennoted that individuals in populations of the

equator tend to have longer limbs than dopopulations living further away from the

equator (in colder environments)


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Allens Rule

- Masia tribe of

East Africa:normally tall andslender: long

limbs assist in theloss of body heat


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Allens Rule

- concerns shape of body, especiallyappendages

- n co er c ma es, s or er appen ages areadaptive because they are more effective atpreventing heat loss


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Whats the suitable body shape inHot climate?

o c ma e


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Response to ColdResponse to Cold

- heat production and heat retention

- Short term responses: increased metabolic rateincreased metabolic rateand shiveringshivering

VasoconstrictionVasoconstriction

- Narrowing of blood vessels to reduce blood

flow to the skin.- Reduces heat loss at the skins surface


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Response to ColdResponse to Cold

Nasal index

- The average ratio of the width to the length of thenose

-

correlated with climate- Noses are narrower in colder regions

- Nose form seems to be adapted to the degree ofneed to moisten the air one inhales


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Adapting to High AltitudeAdapting to High Altitude

Two major kinds of environmental stresses atTwo major kinds of environmental stresses athigh altitude areas:high altitude areas:

1. Alternating daily extremes of climate2. Lower air pressure

- air pressure decreases as altitude increases


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HypoxiaHypoxia oxygen deprivation

- inability to do normal physical activities; lackof appetite, distorted vision, difficulty with

- pneumonia-like symptoms and abnormalaccumulation of fluid around the brain

- reproduction may be affected;low birth weight


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Adult acclimatizationAdult acclimatization occurs in people born at

low elevation upon exposure to high altitude- Increase in respiration rate, heart rate,

roduction of red blood cells

Developmental acclimatizationDevelopmental acclimatization occurs in high-altitude natives

- Greater lung capacity, more efficient (than

migrants) at diffusing oxygen from blood tobody tissues.

human physical adaptation

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