Transcript Plant and Animal Domestication

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
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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
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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
• Seed Dispersal by Animals
• Domesticated only after greenhouses
invented
Fertile Crescent Founder Crops
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Emmer Wheat
Einkorn Wheat
Barley
Lentil
Pea
Chickpea
Bitter Vetch
Flax
North American Crops
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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, recordkeeping
• 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
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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
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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
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Sheep
Goat
Cattle, Oxen
Pig (Actually an Omnivore)
Horse
All are Eurasian
The Lesser Nine
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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