1. Human Variation and Adaptation
Unit 2
Human Variation and Adaptation

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

3. 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

4. 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

5. 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

6. What causes skin color?
How close you or your ancestors were to direct sunlight

7. What causes skin color?
How close you or your ancestors were to direct sunlight

8. 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

9. 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

10. 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)?

11. 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

12. 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

13. 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

14. Genes and Disease Smallpox Bubonic plague (Black Plague)
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

15. 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

16. 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

17. 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

18. 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)

19. 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

20. 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?