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 Selection Seed Scattering Non-bursting pods (peas) Non-shattering heads (grains) Fruits without seeds Germination 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-Domesticates Oaks Food Source in Many Places Grow Slowly Bitterness Controlled By Many Genes Seed Dispersal by Animals Berries 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