Plant and Animal Domestication

Jared Diamond, Guns, Germs, and Steel

Why Farm?• Hunting and gathering can supply a day’s

calories with a couple of hours’ work• Many early farmers less well off than

hunter-gatherers• Line between hunter-gatherers and farmers

is fuzzy– In rich environments, hunter-gatherers may

have permanent settlements (Pacific Northwest)

– May practice some agriculture along with hunting and gathering (Apaches)

The Ice Age and Agriculture• Sea level rise stops about 7000 years ago• Agriculture spreads widely roughly same

time• Stable coastal plain and river valley

environments• Warm, dry climate favors spread of wild

grains• Extinction of megafauna (and

domestication candidates?)

Mediterranean Climate• Dry Summer, Rainy Winter• Favors plants with seeds that can survive

long dry periods• These seeds can be stored for extended

periods• Will not spoil or germinate while dry• Eurasian Mediterranean is world’s largest

zone, greatest ecological diversity in small areas

The Fertile Crescent

Large Seed Grasses• 56 species, <1% of total grass species• Eurasian Mediterranean 32 species• Rest of Eurasia 7 species• Sub-Saharan Africa 4 species• North America 4 species• Mesoamerica 5 species• South America 2 species• Australia 2 species

Human Plant Environments• Select desirable plants in wild• Some seeds, fruits scattered at habitation

site• Other seeds deposited in wastes• Eventually have desirable plants growing

close-by• Protection from foragers• Seed collection

Plant Domestication• More than just planting seeds or

transplanting• Most plants inedible or otherwise unusable• Most plants unsuited for primitive

domestication• Not every locality has abundant plants

suitable for human use• Need nutritional balance• Requires changes in plant characteristics

Highland New Guinea• Simple agriculture for thousands of years• Active experimentation and inquiry• Chronic protein deficiency• Introduction of sweet potato (South America via

Philippines) caused population boom• These people knew their environment as well as

any people on earth• If any local plants could have been successfully

domesticated, they would have found them

Five Levels of Domestication• Unconscious selection of plants for

desirable traits (9000 BC)• Conscious cultivation of plants with desired

traits (BC)• Deliberate breeding to improve traits

(1700)• Scientific breeding: genetic mechanism

known and exploited (1900)• Direct genetic manipulation (2000)

Reversing Natural SelectionSeed Scattering• Non-bursting pods (peas)• Non-shattering heads (grains)• Fruits without seedsGermination Inhibition• Nature: favors seeds that germinate slowly

and over time• Agriculture: favors seeds that germinate

quickly all at once

Reversing Natural Selection

Deterrents• Loss of Toxicity (Almonds)Changes in Reproduction• Asexual Reproduction• Self-Fertilization (Hermaphrodites)Annuals favored: would evolve more quickly

under artificial selection

Plant Domestication

• Single Mutation– Chance of getting multiple favorable mutations

very slim• Self-Pollinated or Asexual Reproduction– Pollination from elsewhere would negate

mutation

Some Non-DomesticatesOaks• Food Source in Many Places• Grow Slowly• Bitterness Controlled By Many Genes• Seed Dispersal by AnimalsBerries• Seed Dispersal by Animals• Domesticated only after greenhouses

invented

Fertile Crescent Founder Crops• Emmer Wheat• Einkorn Wheat• Barley• Lentil• Pea• Chickpea• Bitter Vetch• Flax

North American Crops

• Gourds• Sunflower• Sumpweed (seed crop)• Goosefoot (leaf crop)• Corn (from Mexico)• Beans (from Mexico)• Squash (from Mexico)

Agriculture and Civilization

Why the Link?• Need for organization, surveying, record-

keeping• Surpluses allow development of specialist

classes• Protection?– Grain stores susceptible to raiding

Animal Domestication• Genetic change that makes animal more

amenable to human control• Not the same as:– Taming– Training–Captive Breeding

• A lot more complicated than just capturing and taming animals

Animal Domestication

Happy families are all alike. Every unhappy family is unhappy in its own way.

--Tolstoy, Anna Karenina

Lots of things have to work for success. Failure in any one means failure of it all.

Unsuitable for Domestication• Ferocity (Zebras, Rhinos, Hippos)• High Trophic Level (Carnivores)• Picky Diet (Pandas, Koalas)• Slow Growth (Elephants)• Territoriality (Deer, Antelope)– Large Range– Solitary Habits

• Reclusive Breeding or Elaborate Courtship (Cheetahs)

• Tendency to Panic (Gazelles)

Suitable for Domestication

• Docile (or selectable for docility)• Non-territorial• Dominance Heirarchy (Humans co-opt

leadership role)• Uninhibited Breeding• Rapid Growth a plus

Thyroxine• Governs many growth and maturation

characteristics• Governs adrenaline (fear response)• Low thyroxine traits:– Reduced snout (pedomorphism)– Solid or patchy colors– More frequent reproduction– Larger litters

Self-Domestication

Humans create an environment• Free of Predators• Abundant food• Salt

Animal Domestication

• 148 Species of Large Herbivores (>50 kg)• Eurasia 13/72 (18%) Domesticated• Sub-Saharan Africa 0/51 Domesticated• Americas 1/24 (4%) Domesticated• Australia 0/1 Domesticated

The Big Five

• Sheep• Goat• Cattle, Oxen• Pig (Actually an Omnivore)• Horse• All are Eurasian

The Lesser Nine

• Arabian and Bactrian Camels (Eurasia)• Donkey (Eurasia)• Water Buffalo (Eurasia)• Yak (Eurasia)• Bali Cattle, Mithan (Eurasia)• Reindeer (Eurasia)• Llama (including Alpaca) (South America)

Why Eurasia?

Why Eurasia?

• Only Land Mass with east-west axis• Other barriers– Panama and Caribbean– Rain Forest (Africa)– Trypanosome Belt (Africa)

• Extinction of Megafaunas– Not adapted to humans and vice versa– Possible candidates for domestication wiped

out?

Why Not Domestication?• Buffalo (bison) and elk successfully farmed

in modern times• Have attributes that seem promising for

domestication• Wild grapes in America not cultivated• If advantages marginal, domestication may

not happen even if possible• Indians adapted to Horses Very Quickly

Domesticated Carnivores• Dogs– Have dominance hierarchy that humans can co-

opt• Cats– Probably attracted to prey around grain stores– At best partially domesticated

• Ferrets– Recently popular as pets but long used for pest

control– Probably many of same factors as cats

Small Animal Domestication• Thousands of Candidates• Distinction between Domestication and

Captive Rearing fuzzier– Do We Really Care if a Rabbit is Captive or

Domesticated?• Very Rapid Breeding Cycle