Evolution, 4th Edition

560 CHAPTER 21

brain and a high reproductive rate, we evolved a higher meta-

bolic rate and larger energy budget than any other primate (FIG-

URE 21.17) [58]. Even the leanest humans have much more body

fat than other apes. Humans evolved special cells to store fat not

found in any other primate. These were critical to maintain our

brain and high reproductive rate when food was scarce [41].

The high metabolic rate of humans was made possible by an

evolutionary shift in diet from fruits to meat and tubers. Humans

first obtained meat by scavenging carcasses left by lions and

other predators [57], and later by active hunting. In turn, hunt-

ing selected for the endurance to run long distances, the ability

to throw spears, and many other characters [41]. Judging by liv-

ing hunter-gatherers, such as the Hadza of Tanzania, a hunter

with this lifestyle walks more than 15 km per day. He expends

almost twice as much energy above the basal metabolic rate as

the average American or European today. Humans learned how

to extract even more energy from the meat they hunted by slic-

ing, pounding, and cooking it [83, 84].

Humans became such proficient hunters that each time they

arrived on a new continent, they extinguished many of the large

mammals and birds (the “megafauna”). Mammoths, woolly

rhinoceros, giant bison, giant beaver, diverse South American

ungulates, and the giant ostrich-like moas of New Zealand were among the many

victims [44, 59].

Perhaps the most profound change in human history was the invention of agri-

culture, which first appeared in the Middle East at least 11 Kya. Over the next 5000

years, agriculture was independently invented in China, Mexico, New Guinea,

the central Andes, northern Africa, and the Mississippi Valley of North America

(FIGURE 21.18) [3, 13]. During that time, humans domesticated animals as live-

stock and plants as crops (BOX 21A). Some species, such as rice, were domesticated

independently more than once. Agriculture became widespread across Earth only

about 300 generations ago. In evolutionary time, that is the blink of an eye, and

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Evolution4e_21.17.ai Date 01-10-2017

Body mass (kg)

25 50 100 200

Metabolic rate (thousands of kcal/day)

1

2

(^4) Homo
Pan
Gorilla
Pongo
FIGURE 21.17 Humans have a higher metabolic rate relative
to fat-free body mass than do chimpanzees (Pan), gorillas
(Gorilla), and orangutans (Pongo). (After [58].)
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Evolution4e_21.18.ai Date 01-18-2017
Sorghum
Barley, wheat,
lentil, pea,
chickpea
Soybean,
foxtail millet,
Buckwheat proso millet
Taro,
japonica rice
Taro, lesser
yam, banana
Little millet,
black gram,
mung bean,
indica rice
Teff, nger
millet, yellow
yam, false
banana
Pearl millet,
cowpea,
white yam
Potato,
lima bean,
quinoa
Maize,
cucumber,
sweet potato,
bean, peppers
Sunower,
marsh elder,
goosefoot
FIGURE 21.18 Agriculture was invented
independently at several places around
the world. Some of the crops that were
domesticated are listed. (After [62].)
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