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?