1/14/19
Smil ch. 2
energy return:
how many calories do
you expend hunting (say) a deer, vs. how many calories does the
deer provide?
- how many calories do you
expend growing wheat vs. how many calories does the wheat
you grew provide?
- but this doesn't explain
anthropological and historical evidence very well
- evolution would select the
more efficient societies, but only if their environment was
marginal
- why do societies get food in
ways that are not the most energy efficient?
3.5 million years ago diets changed
to more grassy plants (millet, sorghum, amaranth)
(C4 plants are more heat
tolerant--genetic researchers are trying to develop C4 rice
the need for vitamin C is an
unrelated issue)
it isn't enough to analyze diets based on calories
- you need energy (calories)
- you need protein and fat, you can't live on
carbohydrates alone
- you need vitamins and certain minerals in
order to survive
more on
domestication of plants
and
an animation
1. wild plant food procurement (foraging = hunting and
gathering)
2. wild plant food production (also called intensified food
production)
3. systematic cultivation of wild plants
4. agriculture based on domestic plants
evolution of larger brains required more energy from more
efficient digestion of food (meat, cooking)
- stone tools go back 3.3
million years
- producing a blank that then
makes multiple flake tools goes back 1.5 million years
- tools made of combinations of
materials at leas 500,000 years
- cooking may have started at
least 1.9 million years ago
Foraging societies:
- generally low population density
- hunting was not easy and was a good way to get
energy only when large animals were plentiful (and they
generally aren't)
- gathering and small animals (mostly women's
work) were a large part of the diet (more)
- some groups developed effective methods of
large game hunting and may have been responsible for
extinction of megafauna
- some groups fed themselves with relatively
little work: 2-3 hours a day
- but with limited food storage there were times
of the year when food was scarce and people relied on fat
stores
- some ecologically favorable environments
allowed permanent settlements and high population density
- net energy return doesn't tell us very much
because cultural factors were already important to what people
ate
agriculture resulted from food shortages caused
by population growth or ecological (and climate) change
- net energy return was not usually
better
- agriculture started on the margins of fertile
zones
- plants and animals domesticated concurrently
- except in Africa, the invention spread from
the centers shown on the map above rather than being
re-invented
- imagine inter-planting, particularly in warm
climates (image to the right is an African system in the West
Indies)
- nomadic herding where rain was not sufficient
for agriculture--relatively low labor requirement but also low
population density
Trivia: tomorrow is the 100th anniversary of the
great molasses flood:
https://www.bostonglobe.com/magazine/2019/01/09/the-great-molasses-flood-was-boston-strangest-disaster/VawySumFUf5vKCibM9PLtJ/story.html
