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Human Variation and Adaptation
Unit 2
Outline
Race: A Discredited Concept in Biology Races are not biologically distinct Explaining skin color
Human Biological Adaptation Genes and disease Facial features Size and body build Lactose Tolerance
Race: A Discredited Concept in Biology
Historically, scientists approached study of human biological diversity in two ways: Racial classification Current explanatory
approach; focuses on understanding the differences
Race: A Discredited Concept in Biology
Racial classification (attempt to assign humans to discrete categories based on common ancestry)
Biological differences are real, important, and apparent to us all
In theory, a biological race would be geographically isolated subdivision of a species Humanity lacks this
Race should have shared genetic material, but early scholars used phenotypical (evident, detectable) traits Well, what traits should be primary? Most early scientists used race
▪ Overly simplistic and political
Races are not Biologically Distinct
“Color-based” racial labels don’t accurately describe skin color
Many populations don’t fit neatly in three “great races” Not same facial features,
what color are they? Similar issues when
using any single trait Facial features, height,
weigh
What causes skin color?
How close you or your ancestors were to direct sunlight
What causes skin color?
How close you or your ancestors were to direct sunlight
Explaining Skin Color
Natural selection Skin color influenced
by several genes Melanin is primary
determinant of skin color Darker skin, more
melanin Screens UV radiation
from the sun; offers protection against things like sunburn and skin cancer
Explaining Skin Color
More intense UV radiation poses threats in different areas so lighter skin would be a disadvantage
In cold northern areas, lighter skin absorbs more UV light to make Vitamin D
Modern technology allows people to adapt to different climates and amounts of sunlight
Skin color is balancing: Protection against UV hazards Have an adequate supply of
Vitamin D
STOP – Review Time
What are the two ways scientists classified human biologically diversity?
Are biological differences real? Why or why not?
What are some issues with trying to categorize people into races?
What causes different skin colors (2 things)?
Human Biological Adaptation Several examples of
human biological diversity that reflect adaptation to environmental stresses such as disease, diet, and climate
Adaptations that were once bad may lose their disadvantage if environment shifts
Genes and Disease
More than 10% of the world’s population is affected by tropical diseases
Malaria spreading worldwide Partially because of
increasing resistance to drugs used to treat it▪ Millions of people are
genetically resistant because of Sickle-cell
Genes and Disease
Microbes a huge selective agent for humans
Infectious diseases been bigger threat since food production and agriculture 20,000 years ago
ABO blood groups explain certain resistances
Blood type according to protein and sugar compounds on surface of blood cells This is to help us determine
our cells from invading ones Some microbes have surfaces
similar to our blood cells
Genes and Disease
Smallpox A and AB blood type more
susceptible than B and O Bubonic plague (Black
Plague) O type especially
susceptible▪ Also most likely to get
cholera▪ More resistant to syphilis
In conclusion: whatever blood type you are may make your more or less susceptible to certain diseases
Facial Features
Long noses in arid areas to moisten the air as it is breathed in Cold environments to
warm the air▪ Also puts distance between
brain and super cold air Thomson’s nose rule
Association between nose form and temperature
Other features: Average tooth size▪ Larger teeth for hunters and
gatherers
Size and Body Build
Populations with small individuals are most often found in warm climates and those with greater bulk or mass found in colder regions Bergmann’s Rule:▪ Large bodies found in
colder areas and smaller bodies in warmer ones
▪ Small bodies shed heat more easily and larger ones trap it
Size and Body Build
Zoologist J.A. Allen’s Rule Relative size of protruding body parts –
ears, tails, bills, fingers, toes – increases with temperature
In humans, slender bodies with long digits and limbs in tropical climates
So colder climates, short limbs and stocky bodies
Lactose Tolerance
Many biological traits are not under simple genetic control Some adaptations occur over an individual’s lifetime (phenotypical adaptation) Genes and phenotypical adaptation create lactose intolerance
Ability to drink large amounts of milk (advantage in areas where not a lot of food sources but lots of milk)
Lactose Tolerance
Milk contains sugar lactose▪ The enzyme to digest it is called lactase▪ Lactase production in other mammals ceases after weaning
90% of N. Europeans and descendants can drink it 80% of two African populations can as well Non-herder populations have trouble digesting it
Some can tolerate little or no Some can move from no to low milk diets to high and increase tolerance
STOP – Review Time
What are some ways our genes help us fight disease?
What rule talks about nose size and human climates?
What about body types? Which body types tend to be in which climates?
Lactose tolerance is usually found in what populations?
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