Farmer Power

• Farmers have greater numbers than hunter/ gatherers 10 or 100 to 1
• Own better weapons and armor
• Have more powerful technology
• Have centralized governments with literate elites:  better able to wage wars of conquest
• Breathe out nastier germs.

Major Killers
Major killers of humanity throughout recent history are all infectious diseases that evolved from diseases of animals

• Smallpox
• Flu
• Tuberculosis
• Malaria
• Plague
• Measles
• Cholera

Disease victims in war

• Until WWII, more victims of war died of disease than battle wounds.
•  95% of Native Americans died from diseases brought by Europeans.
• Why not the other way around?
• Europeans had the animals and the large populations that produced the diseases.

• Passively (ex: salmonella)
• Insect vector (ex: malaria, plague, typhus, sleeping sickness)
• Lesions (ex: syphilis, smallpox)
• Coughing  (ex: flu, cold, whooping cough)
• Diarrhea (ex: cholera).

How We Respond to Diseases

• Fever (bake out microbe)
• Immune response: This may give us lifelong immunity (measles, mumps, rubella, pertussis, smallpox) or not, if microbe evolves quickly (flu, malaria, sleeping sickness, AIDS)
• Natural selection: Not everybody dies, resistant genes selected for in population.

• Epidemic diseases spread quickly to an entire population
• Run their course quickly
• Result in either death or resistance.
• Tend to be restricted to humans.
• Examples: measles, rubella, mumps, pertussis, smallpox.

Epidemic Diseases in History

• Flu killed 21 million people at end of WWI.
• Black Death killed 1/4 of Europe's population between 1346 and 1352.
• Disease dies out if population is under a half million because everybody has been exposed and is either dead or resistant.
• Disease only survives with travel between populations or between uninfected pockets within a population.
• These diseases cannot sustain themselves in small populations of hunters/gatherers

• ones that can live in animals: yellow fever
• ones  that take a long time to kill: leprosy
• ones that humans don't develop immunity to.  ex: worms and parasites

• Why did agriculture launch the major infectious diseases?
• High human populations
• Sedentary life among sewage
• Close proximity to herd animals

Disease Transfer from Animals
Four stages of animal to human disease transfer:

• 1) diseases directly from animals.  Don't get transmitted human to human. Example: brucellosis from cattle, leptospirosis from dogs
• 2) Does transfer human to human, but dies out.  Example: Fort Bragg fever in 1942
• 3) Transfers human to human but not yet long-established.  Example:: Lyme disease, AIDS
• 4) long established epidemic diseases. Diseases evolve to effectively work in new host.  Example: syphilis

• Diseases played huge part in conquest of New World.
• Hispaniola had 8 million inhabitants in 1492, zero by 1535.
• There were estimated 20 million Indians in USA before European diseases.  19 million died
• Also 20 million in Mexico, reduced by disease to 1.6 million.
• With 20 million, why not more infectious diseases?  Answer: No large domestic animals.

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