Agriculture, plant physiology, and human population growth: past, present, and future
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OPINION
Agriculture, plant physiology, and human
population growth: past, present, and future
Lincoln Taiz
University of California, Santa Cruz, CA, United States of America.
*Corresponding author: ltaiz@ucsc.edu
Received: 24 August 2013; Accepted: 26 August 2013
When we gaze at our beautiful blue planet as seen from food production has not only kept up with population growth, but
space (Figure 1A), it’s difficult to believe that a single species also has become a driver of population growth (Evans 1998).
could have such a profound impact on earth’s climate, but that As noted by Jared Diamond, the author of Guns, Germs, and
is exactly what is happening. To put it bluntly, we humans have Steel, agriculture is “an autocatalytic process, that catalyzes itself
been too creative and too reproductively successful for our own in a positive feedback cycle.” Each major advance in agriculture
good (Figure 1B), and our success has brought about the four was accompanied by an increase in the rate of population growth.
major challenges we face today: loss of biodiversity, pollution, Mazoyer and Roudart (2006) identified three major inflection
climate change, and food insecurity. points (Figure 1C): first, the Neolithic agricultural revolution,
If we examine human population growth, modern humans which began at around 8,000 BC; the Neolithic Revolution was,
evolved around 200,000 years ago, and for most of that time they without question, the golden age of crop creation, the most
survived as hunter-gatherers. By 8,000 BC, the population increased radical phase of agriculture, which brought more drastic changes
to about 10 million people. The invention of agriculture eventually to wild species than has since been achieved by scientific plant
led to urbanization, and the population had grown to 50 million by breeding and genetic engineering. Second, the hydroagricultural
the Bronze Age. By the time of Christ, the population had increased or irrigation revolutions in the Near East, which began around
to 250 million, before reaching its first billion by the middle of the 3,000 BC. Third, the medieval and modern agricultural periods,
eighteenth century. After that, the human population increased to which began around 1,000 AD.
seven billion in just two hundred years. By 2050, if all goes well, we’re Let us examine the relationship between agriculture and
supposed to finally level off at about nine billion. population in a little more detail, beginning with the agricultural
In 1798, when the human population was “only” one billion, revolution, which enabled the population to increase to 50 million.
the British cleric Thomas Malthus published his famous Essay on the For reasons that are still poorly understood, modern humans
Principle of Population, in which he compared the geometric growth began to live in permanent settlements located near abundant
of human populations to the arithmetic growth of the food supply wild food supplies around 8,000 BC (Figure 2). They soon began
and predicted that population growth would soon outstrip our ability planting gardens, and this led to the domestication of three types
to feed ourselves. Malthus was wrong for a couple of reasons: First, of staple crops — cereals, legumes, and roots or tubers. The earliest
he underestimated human resourcefulness and second, he did not domesticated food crops were in the Fertile Crescent and included
anticipate modern birth control methods. Contrary to his predictions, Emmer and Einkorn wheat, barley, pea, lentil, chickpea, and bitter
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 167
Lincoln Taiz
A B
Mazoyer and Roudart: A History
C of World Agriculture (2006)
Total human
population in millions
50
Agriculture is “an autocatalytic 7000
process-one that catalyzes itself 40
Neolithic agricultural
in a positive feedback cycle...” revolution
30
-Jared Diamond in Guns,
Upper Paleolithic 20 The Agricultural
Germs, and Steel 1 revolutions
10 of Modern Times
5 5
-40 000 -8 000 -3 000
(-40 000) (-10 000) (-5 000)
Wet rice growing Agricultural
500
Population revolution of the
scale x 20 Hydroagricultural Middle Ages
civilizations
(the Nile, Mesopotamia, 3
The Indus) 250
Neolithic agricultural
Upper revolution 2 100
Paleolithic 0 1 000 2 0
1 50
-40 000 -8 000 -3 000 0 1 000 2013
Common era
(-40 000) (-10 000) (-5 000) (-2 000) ⎛present⎞
Golden Age of ⎝ 0 ⎠
Crop Creation
Figure 1. Agriculture and population growth. (A) The earth as seen from space (NASA); (B) Big crowds provide a metaphor for overpopulation
(http://lookingtobusiness.com/wp-content/uploads/2010/11/A-picture-of-a-crowd-of-people.jpg); (C) Major inflection points in the
growth of human population correlated with the development of agriculture (from Mazoyer and Roudart, 2006, p. 65).
168 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013
Agriculture, plant physiology and humankind
Feeding the
Formation of permanent
First Fifty (Causes poorly
foraging settlements
Million People understood)
near food supplies
Cultivation of wild Tools: Axe, fire,
plants in gardens. digging stick, hoe
Cave painting of
3,000 year old
grain- harvesting Domestication of key Conscious or
World Population
scene in Algeria staple crops: accidental
selection
50
Neolithic agricultural 40
revolution
30
Upper Paleolithic 20
5
10
5
cereals
-40 000 -8 000 -3 000
Wheat Barley Maize Rice Sorghum
(-40 000) (-10 000) (-5 000)
50 Million legumes
8,000 BC - 3000 BC
Lentil Chickpea Soybean Common Bean
roots/
tubers
10 Million
160,000 BP - 8000 BC
Potato Cassava Sweet Potato Yam
BC
Figure 2. Feeding 50 million people.
vetch. The combination of cereals and legumes provided all the the spikelets have smooth abscission zones. In contrast, the
essential amino acids needed for human nutrition. spikelets of domesticated wheat varieties all have rough
Agriculture arose independently at least seven times surfaces where the rachis breaks during threshing. In addition,
around the world — between 10,000 and 4,000 years ago. the domesticated wheat varieties have larger seeds and
Each of these seven major centers of domestication involved germinate more rapidly and uniformly than the wild variety.
its own suite of crop species. For example, rice and millet were Polyploidy played crucial roles in the evolution of
the primary domesticates in Asia; sorghum was domesticated domesticated wheat. Einkorn was diploid, Emmer and Durum
in Africa; maize, squash, and beans were domesticated in wheats were tetraploid, and the bread wheats were hexaploid.
Mexico; South America gave us the potato and sweet potato; First, the diploid Einkorn wheat hybridized with the diploid
and North America domesticated sunflowers. Domestication Aegilops, or goat grass, followed by polyploidization to produce
typically involved selecting some or all of the following the tetraploid Durum wheat, composed of two different diploid
genetic traits: increased reproductive output, non-dehiscent genomes, AA and BB. Next, Durum wheat hybridized with
fruits, self-pollination, larger seeds and fruits, loss of seed another diploid goat grass to produce a triploid hybrid, followed
dormancy, rapid and uniform germination, uniform ripening, by yet another polyploidization event to produce the hexaploid
annual life cycle, and palatability. For example, during wheat bread wheat, with three diploid genomes — AA, BB, and DD.
domestication, there was unconscious selection for mutants Domesticated maize evolved from one of the teosintes:
with non-shattering ears that would not fall apart during Zea mays ssp. parviglumis. There are four subspecies of Zea
harvesting. You can easily recognize the wild forms because mays: huehuetenangensis, mexicana, parviglumis, and mays.
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 169
Lincoln Taiz
The first three are the teosintes, and domesticated maize is manure and by planting legumes, the so-called green manures.
Zea mays ssp. mays. The transformation of teosinte into maize Crop rotation and fallowing were also practiced for the first
was one of the most dramatic changes in the history of plant time. Irrigation gave rise to the great Bronze Age civilizations of
domestication. The major change was the fasciation of the Mesopotamia and Egypt. Many new perennial crops, especially
teosinte inflorescence, giving rise to the maize cob with its fruit and nut trees and vines, were domesticated. Unlike the
numerous rows of kernels. Recent studies by Bommert et al. annual crops, the perennial crops were mostly outcrossers, so
(2013) have identified the FASCIATED EAR2 locus, which they would not breed true from seed. Therefore, they had to be
regulates the number of rows of kernels in maize cobs. Genes propagated vegetatively or by grafting. In the case of dioecious
that regulate fasciation could potentially increase the yields of species, such as figs, dates, and pistachios, artificial pollination
other cereals. Imagine, for example, a cob of wheat! was practiced. Thus, the art of horticulture was born. This was
Between about 3,000 BC and 800 AD, the population also the period when most of our delicious vegetables were
grew fivefold from 50 million to 250 million people (Figure 3). domesticated in both the Old and New Worlds, providing
How did agriculture keep pace with this population growth? important nutritional benefits and dietary variety.
During this period, agriculture spread from its seven centers of Between 800 AD and 1825 (a thousand years), the
domestication throughout Eurasia and the Americas. As more population quadrupled in size to one billion people (Figure 4).
and more people began farming, more and more land was During this period, crops became globalized by two important
cleared and cultivated. Oxen, and later horses, were harnessed historical events. First, the spread of Islam brought Asian and
to plows for the first time, greatly increasing the efficiency of African crops to Europe, and vice versa. Second, the arrival of
cultivation. Farmers learned to fertilize their soils with animal Columbus in the New World led to an exchange of New World
Feeding the Diffusion of agriculture throughout Eurasia and the Americas
First 250
Million People
Land expansion: clearing Ox-drawn ard (scratch plow),
forests, plowing grasslands, heavy plow, horse collar
terracing hills
Soil fertilization: animal manures, green manures (legumes),
and crop rotation with fallowing.
Irrigation
World Population
Vegetative propagation,
artificial pollination,
Domestication of perennial crops grafting
Clonal propagation/Artificial pollination Grafting/Artificial pollination
-
( )
-
Olives Grapes Figs Dates Pistachio Apples Pears Plums Cherries
250 Million
3000 BC - 800 AD
Domestication of vegetable crops (Old and New World)
50 Million
8,000 - 3,000 BCE
Lettuce Cole Crops Squash Chili peppers Beets Tomato Onions Carrots
Figure 3. Feeding 250 million people.
170 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013
Agriculture, plant physiology and humankind
Spread of Islam and
Globalization of world crops
Feeding One Columbian Exchange
Billion People
Asian Crops
2050-9 billion
9
8
Sugar cane Bananas Lemons Eggplant Artichoke Mango Coconut
7
2006-6.5 billion
6
Billions of people
5
4
Billion
3
1945-2.3 billion
2
1 New World Crops
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
0 10 million 50 million 250 million
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
World Population
Kidney beans Maize Sweet potato Potato Squash Peanuts Avocado
Importation of animals
to the New World.
Earthworms Honey bees Draft animals
1 Billion
800 AD - 1825 Expansion of arable land by deforestation, etc.
Drilling crops in rows instead of scattering seed
250 Million
3000 BC - 800 AD
Four-course crop rotation in Europe (wheat, turnips, barley, clover)
combines N2-fixation with animal manure, and eliminates fallowing.
50 Million
8000 BC - 3000 BC Increased yields by 50%
Figure 4. Feeding the first billion people.
and European crops known as the “Columbian Exchange.” In alternated with turnips and clover, with turnips being used as
addition to livestock — such as cattle, pigs, sheep, goats, and animal feed (resulting in the production of manure) and clover
chickens — Europeans brought other animals to the New World enriching the soil through nitrogen fixation. The four-course
that greatly facilitated agriculture. For example, earthworms, rotation procedure increased yields by about 50%.
which had died out in the northeastern United States during the It took 200,000 years for the human population to reach
last ice age, transformed the forests of New England by digesting one billion people, but only a hundred years to go from one
all the surface litter, to which the trees had been adapted. They to two billion in 1927 (Figure 5). The most important factor
also conditioned the soil for future cultivation by introducing air enabling the food supply to keep pace with population growth
and organic matter. The importation of European honey bees, was farmland expansion. During this period, there was a
which are pollination generalists, ensured that the newly arrived doubling of the land cleared for agriculture in the United States
Old World crops would be pollinated, and imported draft and a tripling of the arable land in Russia. Wheat production
animals provided the power for plowing the land. spread westward between 1839 and 1909. This westward
Particularly in the New World, this was a period in expansion was made possible by extensive breeding programs,
which there was considerable expansion of arable land by which created new wheat varieties that could be grown
deforestation and the plowing of grasslands. Crop yields were in these regions, resulting in an eightfold increase in US
further enhanced by the practice of drilling crops in rows, wheat production.
instead of by scattering seed. A four-course system of rotation This same period also saw the beginning of agricultural science.
was adopted in England and elsewhere: wheat and barley were Major gains in crop yields were achieved as a result of increased
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 171
Lincoln Taiz
Doubling of land cleared for agriculture in U.S. and Russia.
Feeding Two
Billion People
*Beginning of agricultural science*
Liebig’s “Law of the Minimum” (1840) and the demonstration that
nitrogen, potassium and phosphate are essential nutrients.
2050-9 billion
9
8
7
2006-6.5 billion
6
Billions of people
5
4
Introduction of N, P and K fertilizers: Chilean nitrate, Peruvian guano,
Billion
3
2 German potash, and superphosphate.
1945-2.3 billion
2
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
0 10 million 50 million 250 million
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
Haber-Bosch process (1913) for industrial nitrogen fixation (N2+3H2→2NH3)
World Population
makes abundant, cheap nitrogen fertilizer available.
Bordeaux mixture used to combat downy mildew in grapes (1885);
2 Billion Paris green used to protect potatoes from beetles (1900).
1825 - 1927
Discovery of trace nutrients: calcium, magnesium, sulfur, iron
1 Billion Discovery of atmospheric N2-fixation in legume root nodules.
800 AD - 1825
Mendelian genetics inaugurates era of targeted plant breeding.
250 Million
3000 BC - 800 AD
Discovery of photoperiodism (1920) facilitates breeding of new soybean
varieties adapted to different latitudes.
50 Million
8000 BC - 3000 BC
Discovery of first plant growth hormone, auxin (1926).
Figure 5. Feeding two billion people.
scientific understanding of plant nutrition and disease resistance. both of which were pioneered in France: Bordeaux mixture
An important breakthrough was Liebig’s demonstration that was first used to protect grapes from downy mildew, and Paris
nitrogen, potassium, and phosphate were essential nutrients. Green, once used to kill rats in Paris sewers, was found, at lower
Liebig’s “Law of the Minimum,” published in 1840, which stated concentrations, to protect crops, like apples, from insect pests.
that crop yields are always limited by the essential nutrient in In addition to the practical gains from fertilizing and the
shortest supply, came as a revelation to farmers who had assumed chemical control of pests and diseases, important theoretical
that soil fertility mainly depended on the amount of nitrogen. advances laid the foundation for future increases in crop
Of course, nitrogen was the limiting factor for soil fertility in most yields. These include the identification of several trace
cases; so the importation of nitrogen-rich fertilizers from the elements (calcium, magnesium sulfur, and iron); the discovery
New World in the form of Chilean nitrate and Peruvian guano of nitrogen fixation in legume root nodules; the advent of
greatly increased crop yields in Europe, as did German potash, or Mendelian genetics, which greatly accelerated the process
potassium salts, and superphosphate, a soluble form of phosphate. of plant breeding; the discovery of photoperiodism, which
By the early twentieth century, however, the supply of cheap facilitated breeding for new varieties adapted to different
nitrogen fertilizer from South America was beginning to decline. latitudes; and the discovery of the first plant hormone, auxin.
Fortunately, the Haber-Bosch process for industrial nitrogen The population went from two billion to three billion
fixation came along in 1913, providing a virtually unlimited supply from 1927 to 1960, and this time it took only 33 years to add
of cheap nitrogen fertilizer for farming. The other breakthrough another billion people (Figure 6). A huge increase in arable
came in the form of copper-based fungicides and insecticides, farmland during this period made it possible to feed all those
172 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013
Agriculture, plant physiology and humankind
Global arable land expanded by 40%, plus additional 15% by shifting
Feeding Three from feed for horses to human food= 53% total increase.
Billion People
Farm mechanization replaces mules, horses, and people.
2050-9 billion
9
DTT used to protect field crops and fruit trees against insects.
8
7
2006-6.5 billion
6
Billions of people
5
4
3
Billion
3
1945-2.3 billion
2, 4-D used as herbicide to increase yields of cereal crops.
2
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
0 10 million 50 million 250 million
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
Irradiation and chemical mutagens used in plant breeding
World Population
3 Billion
1927 - 1960 Colchicine used to create fertile hybrids, e.g. Triticale (rye:wheat)
Introduction of hybrid maize varieties doubles U.S. maize yields.
Improvement in Yield Potential by Breeding
2 Billion 10
1825 - 1927
9
Yield or yield potential (t ha-1) 8
But:
7
1 Billion 140
800 AD - 1825 N Fertilizer
6 120
5 100 100 2.0
1. Negative impacts of excess % Area in U.S.
Herbicide use (kg ha-1)
N use (kg ha-1)
fertilizers, DTT, and herbicides 4 Sown to Hybrids 80 80 1.6
250 Million
on environment.
% hybrids
3000 BC - 800 AD 3 60 60 1.2
2. Increase in water usage. Maize Yield
2 40 40 0.8
3. Dependency on fossil fuel.
4. Growing gap between rich and 1 Herbicides 20 20 0.4
50 Million poor nations. 0 0 0 0
8000 BC - 3000 BC
1900 1920 1940 1960 1980
Year
Figure 6. Feeding three billion people.
hungry mouths. The total arable land for food increased during also a problem, as was the overapplication of fertilizers, which
this period by a total of 53%. The twentieth century’s greatest got into the water supply and caused algal blooms. Increased
expansion of farmland took place in Brazil, where the arable land water usage for irrigation led to the overpumping of aquifers,
increased tenfold between 1900 and 1950. Farm mechanization while farm mechanization and the liberal use of fertilizers both
also enabled farms to be more efficient and productive, replacing consumed large amounts of fossil fuel. Perhaps most troubling,
mules, horses, and people. The insecticide DTT was introduced the growing cost of modern agriculture began to open up a
to protect crops from insects. DTT was extremely effective and huge gap in food availability between rich and poor nations.
much less toxic than the older insecticides. And the synthetic The world population reached four billion in 1975, and
auxin 2,4-D was widely used as an herbicide for cereal crops. this time it only took 15 years to add the next billion people
Plant breeders also began to use irradiation and chemical (Figure 7). The biggest gain in food supply was the result of
mutagens to speed up the selection process; and colchicine was the so-called Green Revolution. The term “Green Revolution”
introduced to induce polyploidy and create new fertile hybrids, refers to the introduction in the 1960s of high-yielding, semi-
such as the wheat/rye hybrid Triticale. Finally, hybrid maize was dwarf varieties of wheat and rice. These semi-dwarf varieties
introduced, doubling US maize yields over this period. responded to nitrogen fertilizer without lodging and were
But there were some negative environmental impacts of disease resistant as well. Historically, fully mature wheat stalks
these advances as well. In her influential book Silent Spring, were as tall as the workers who harvested them. In contrast,
naturalist Rachel Carson brought the toxic effects of DTT to the semi-dwarf varieties developed by Norman Borlaug and
the public’s attention in 1962. The overuse of herbicides was his colleagues in Mexico are knee-high. The new semi-dwarf
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 173
Lincoln Taiz
varieties have a much higher harvest index, or grain to stalk propagation; the first use of chemical selection in plant
ratio (Figure 7, left graph). The higher harvest indices of breeding, which led to the creation of Canola oil by eliminating
the new semi-dwarf varieties led to a remarkable increase in the erucic acid from Brassica napus seeds; and last but not least,
wheat and rice yields in developing countries (Figure 7, right the discovery of the Ti-plasmid of Agrobacterium tumefaciens
graph), which was all the more remarkable because it occurred by Schell, Montegu, and Chilton in 1974 set the stage for the
with only a negligible increase in the amount of farmland. creation of an ever-expanding list of GMO crops.
On the negative side of the ledger, however, the new crops We went from four to five billion people in only 11 years,
increased the amount of fertilizer, pesticide, and water used in from 1975 to 1986 (Figure 8). Thanks largely to the continuing
agriculture still further and caused a large decrease in crop benefits of the Green Revolution, the food supply kept pace
genetic diversity as well. So there were significant environmental with population growth without increasing the amount of
downsides to the Green Revolution, as critics have pointed out. farmland. Wheat and rice yields kept pace with the increase in
Other factors that increased yields and helped to feed population. But, this increase in crop yield was accompanied
the four billion people were the switch to multiple cropping by a big increase in nitrogen fertilizer use, as well as a slight
in many Asian countries; the introduction of glyphosate, or increase in irrigation (Figure 8, graph). Once again, there was
Roundup, as an herbicide, which was extremely effective and no significant increase in the total amount of arable land.
less environmentally hazardous than the older herbicides; Promising new developments during this period included
the introduction of tissue culture techniques for clonal the beginning of no-till and minimum tillage agriculture, which
“Green Revolution”: High-yielding, nitrogen-responsive, non-lodging, disease-resistant,
Feeding Four semi-dwarf wheat and rice varieties.
Billion People
0.55 Wheat yields in developing countries, 1950-2004
% Plant Weight in Grain 3000
0.50
2050-9 billion
2500
9
Harvest index
8
2006-6.5 billion
7
6
0.45
2000
Yield (kg/Ha)
Billions of people
5
4
4
Billion
3
0.40
1945-2.3 billion
barley
2
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
1500
0 10 million 50 million 250 million
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
0.35 rice
wheat
1000
World Population
0.30
1880 1900 1920 1940 1960 1980
Year of release 500
Figure 25 The rise in the harvest index of wheat, rice 1950 1960 1970 1980 1990 2000
and barley varieties with the year of their release58. Source: FAO
But: Downsides of Green Revolution: High fertilizer, pesticide, and water use; soil salination
4 Billion from irrigation, loss of crop genetic diversity.
1960 - 1975
Multiple cropping in Asia (e.g. wheat and corn in China).
3 Billion
1927 - 1960 “Roundup” (glyphosate) herbicite introduced.
Tissue culture techniques applied to plant breeding.
2 Billion
1825 - 1927
Chemical selection technique used to eliminate erucic acid from Brassica napus seeds
to create Canola oil (1974).
1 Billion
800 AD - 1825
Discovery of Ti-plasmid by Schell, Montagu, and Chilton (1974/5)
Figure 7. Feeding four billion people.
174 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013
Agriculture, plant physiology and humankind
Feeding Five The average world yields of the staple cereals keeps pace with population growth,
Billion People with no net increase in arable land.
2050-9 billion
9 6 1.8 3.6
8
World average wheat and rice yields (t ha-1)
7
2006-6.5 billion
1.6 3.2
6
5
Billions of people
5
4
5 Leveling off of arable land
Billion
Arable or irrigated area (109 ha)
3
1945-2.3 billion
2 1.4 2.8
Population (billions)
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
0 10 million 50 million 250 million
First modern humans
arable area
0
4
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
1.2 2.4
1.0 2.0
3 rice
Fertilizer N (106 tonnes)
0.8 80 1.6
2
World Population
0.6 60 1.2
wheat
5 Billion 1
population 0.4 40 0.8
1975 - 1986 fertilizer N
0.2 20 0.4
irrigated
area
0 0 0 0
1860 1880 1900 1920 1940 1960 1980 2000
Year AD
4 Billion
1960 - 1975 Minimum tillage, combined with Roundup and glyphosate-resistant crops decreases soil
erosion, soil oxidation, and reduced fuel use.
3 Billion
1927 - 1960
Progress in the Genetic Engineering of Plants
2 Billion 1. Transfer of antibiotic-resistance genes from bacteria to plants via Ti plasmid of
1825 - 1927 Agrobacterium tumefaciens (1984).
2. Development of the DNA gun (1987).
3. First transfer of Bt toxin genes from bacteria to plants (1987).
4. TMV-resistant tobacco, tomato, and petunia produced by overexpressing coat
1 Billion protein using 3SS promoter (1980s)
800 AD - 1825
Figure 8. Feeding five billion people.
can decrease soil erosion, soil oxidation, and fuel consumption. More promising was the first unveiling of the first GMO
Much progress was also made in genetic engineering during crop in 1994, the “Flavr-Savr” tomato. Flavr-Savr had been
the 1980s. Plant transformation was achieved using the transformed with the antisense gene for polygalacturonase,
Ti-plasmid and the DNA gun. The bacterial gene for Bt toxin which inhibited cell wall softening. In theory, this would
was put into plants, and the first virus-resistant plants were allow the tomato to ripen on the vine before being picked and
produced by overexpressing TMV coat protein genes using the shipped. However, Flavr-Savr tomatoes still softened enough
35S promoter. during shipping to require expensive packaging, so it was
In the year 2000, it took about the same amount of time withdrawn from the market in 1996.
to go from five billion to six billion as it took previously to The year 1996 saw the introduction of the first glyphosate-
go from four billion to five billion — suggesting that the resistant crops, which were quickly adopted by many countries
rate of population growth had finally stopped accelerating around the world. In the year 2000, Ingo Potrykus and his
(Figure 9). This was the good news. The bad news was that colleagues published their paper on Golden Rice in Science.
we still had another billion mouths to feed. Unfortunately, By supplying a source of vitamin A, Golden Rice holds out the
the growth rate of cereal production fell to 1% per year, promise of saving hundreds of thousands of Asian children
down from 1.6% in the 1980s and almost 3% in the 1970s from blindness every year. It is slowly gaining acceptance, but
(Figure 9, graphs). This was partly due to economic factors, because of resistance to GMO foods its status as a crop is still in
and partly due to the exhaustion of the benefits derived limbo. In 1995, the first Bt-maize crop was put on the market.
from the Green Revolution. By 1999, 12 million hectares of Bt maize, potato, and cotton
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 175
Lincoln Taiz
Feeding Six
Billion People In the 1990s, the growth rate of world cereal production fell to 1% per year, down from
1.6% in the 1980s and amost 3% in the 1970s. (FAO)
Tons Per Hectare Wheat - yield in Britain since 1890
2050-9 billion
6 Tons Per Hectare
9
8
7
10 9.0
6 Rice in Asia
2006-6.5 billion
6
8.0
8 Wheat in France Wheat in Britain 5
Billions of people
5
4 7.0
Japan
Billion
4
3
1945-2.3 billion
6.0
Grain yield - t/ha
6
2
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion
5.0
1
0 10 million 50 million 250 million
3
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
4.0
4 China
3.0 2
2.0
2 1
1.0
Source: FAO Source: USDA
0 0.0 0
1960 1970 1980 1990 2000 2010 2020
6 Billion 1960 1970 1980 1990 2000 2010 2020
1890
1895
1900
1905
1910
1915
1920
1925
1930
1935
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
World Population
1985 - 2000
Flavr Savr tomato first GMO crop, based on antisense gene for
polygalacturonase: 1994 to 1996.
5 Billion
1974 - 1985
Glyphosate-resistant crops introduced (1996)
4 Billion
1960 - 1975 Golden Rice paper by Ingo Potrykus, rejected by Nature without
review, published in Science in 2000.
3 Billion
1927 - 1960 First Bt-crop (maize) introduced (1995); 12 million hectares of Bt maize,
potato, and cotton grown globally by 1999.
2 Billion
1825 - 1927
Discovery of co-suppression phenomenon in Petunia by Jorgensen (1990), later shown
to be based on RNAi. RNAi is also the mechanism of virus-resistance conferred by the
1 Billion over-expression of coat proteins (e.g. potato, tomato, papaya, squash, soybean).
800 AD - 1825
Figure 9. Feeding six billion people.
were being grown globally, significantly reducing the amount of Alaska. The United States is still the largest planter of GM
of pesticide use. In addition, co-suppression was discovered crops, with Brazil the next largest (Figure 10, left chart).
in Petunia by Jorgensen. The mechanism of co-suppression An encouraging sign is that the area of land planted in GM
was subsequently shown to be based on RNAi, and RNAi crops in the developing world, indicated by the red curve, is
turned out to be the basis of the virus resistance induced by now equal to that in the developed world, shown by the blue
overexpressing viral coat proteins. In short order, a number of curve (Figure 10, right graph). Among the benefits of GMO
virus-resistant crop plants were produced, including potato, crops is a decrease in pesticide use. According to Brookes
tomato, papaya, squash, and bean. and Barfoot (2010), the growing of Bt-maize alone resulted
Which brings us to 2013 (Figure 10). Today, the human in a 35% decrease in insecticide use between 1996 and 2008.
population stands at about seven billion people. Although GMO crops can also help protect against soil erosion. The use
crop production is still increasing, it is increasing at a far of glyphosate in conjunction with minimum tillage agriculture
slower rate than in the 1960s, suggesting that the benefits could prevent soil erosion and reduce greenhouse gas emission
of the Green Revolution are effectively over. We need a new caused by soil oxidation. On the negative side of the ledger,
Green Revolution — a “Gene Revolution” — to boost crop some weeds are evolving resistance to glyphosate, and some
yields still higher. Despite opposition in some countries, insects are developing resistance to Bt toxins. This is simply
more and more farmers around the world are planting GM natural selection at work and should come as no surprise.
crops. The total land area planted in GM crops is now 100× As old defenses become ineffective, new ones will have to
more than it was in 1996 and is equivalent in area to the state be discovered.
176 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013Agriculture, plant physiology and humankind
Feeding Seven
Billion People
End of the stimulus from the first Green Revolution - we need a second Green Revolution.
2050-9 billion
9
8
2006-6.5 billion 7
7
6
GM crop land area (soybean, cotton, maize, canola) is 100X what it was in 1996, equivalent
Billions of people
to the state of Alaska.
5
4
Billion
3
1945-2.3 billion
2
POPULATION GROWTH THROUGHOUT HISTORY
1776-1 billion 1
0 10 million 50 million 250 million
First modern humans
0
200 million mya 10,0 8,000 BC 6000 BC 5000 BC 4000 BC 3,000 BC 2000 BC 1000 BC 1 AD 1000 AD 1850
Top GMO crop growing countries, in million hectares (2012) GLOBAL AREA OF BIOTECH CROPS
Million Hectares (1996-2012)
70 180 Total Hectares
28 Biotech Crop Countries
160 Industrial
60 Developing
140
7 Billion 50
120
World Population
2000 - 2013 40
100
30 80
20 60
10 40
6 Billion 20
1985 - 2000
USA Brazil Argentina Canada India China Paraguay South Pakistan Uruguay 0
Africa
Source: ISAAA 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
5 Billion
1974 - 1985
4 Billion
1960 - 1975
From 1996 to 2008 the cumulative decrease in insecticide use on Bt maize was 35%
(29.9 million Kg) globally. (Brookes and Barfoot 2010)
3 Billion
1927 - 1960
Major Concern: Weeds are developing resistance to glyphosate and insects are becoming
resistant to Bt toxin.
2 Billion
1825 - 1927
Figure 10. Feeding seven billion people.
Because of the ongoing need to feed people, agriculture biodiversity loss. Agriculture is thus a Faustian bargain. In the
dominates the planet today. Nowhere is this phenomenon immortal words of the cartoon character Pogo, “We have met
more apparent than in Brazil. Brazil’s agricultural output has the enemy, and he is us!”
been increasing faster than that of any other country, mostly Despite the dominance of agriculture in the world today,
notably in the cerrado, where farmers have converted vast hunger and malnutrition persist in the developing world.
stretches of grassland with acidic and nutrient-poor soils Nearly one billion people, about 70% of whom are located
to agricultural powerhouses by the addition of lime and in Asia and East Africa, are malnourished according to U.N.
phosphorous. What’s happening in the cerrado illustrates statistics. At the same time we are in the midst of a global
just how dominant agriculture is in the world today, and obesity epidemic! There are now about 1.6 billion obese
as with all major gains in food production it comes at an people globally. The problem is that some people in the
environmental cost. more affluent nations are eating enough food for two or
According to Jonathan Foley, agriculture takes up 40% of three people, while others are going hungry. Unsurprisingly,
the global land area, which includes 12% for food crops and Americans are the worst offenders. But as economic
28% for pastures. Agriculture also uses 70% of the global conditions improve and more and more people enter the
water withdrawals and generates 30% of greenhouse gases. middle class, they are going to want the same abundance of
In addition, agriculture is a major source of nitrogen and food that the rich nations have. They are also going to want to
phosphorous flows in the ecosystem and a massive driver of eat higher up on the food chain — i.e., more meat — which
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 177Lincoln Taiz
will require even greater increases in crop production to feed
THE CURRENT YIELD TRENDS ARE INSUFFICIENT TO DOUBLE CROP
all the additional livestock. Trying to prevent this trend is PRODUCTION BY 2050 (2.4% PER YEAR)
probably a futile exercise. 12
To keep pace with both population growth and potential Maize
2.4%
10
economic improvement, the prevailing opinion is that we Rice
Wheat 1.6% (67%)
will have to double the current rate of food production in 8 Soybean
order to feed nine billion people by 2050 (Figure 11). Can
Yield tons/ha
we do this? To double food production by 2050, Ray et al. 6 1.0% (42%)
(2013) have calculated that crop yields would have to grow 0.9% (38%)
4
1.3% (55%)
at a rate of 2.4% per year. But the current growth rates of
world crop yields for maize, rice, wheat, and soybeans are 2
well short of 2.4%. In fact, crop yields are increasing at less
0
than half the required rate (Figure 12). How, then, are we 1970 1980 1990 2000 2010
Years
2020 2030 2040 2050
going to feed nine billion people by 2050? Ray DK, et al. (2013) Yield Trends Are Insufficient to
Could we increase crop production by expanding the Double Global Crop Production by 2050. PLoS ONE 8(6)
amount of croplands? The answer to the question, is yes we
Figure 12. Actual trends for the rate of increases of crop yields for
could potentially increase the amount of arable farmland, maize, rice, wheat, and soybean compared to the 2.4% rate increase
but it would come at a prohibitive ecological cost. Most required to feed nine billion people by 2050 (Ray et al. 2013).
Current Assessment: To keep pace with population growth and the growth of the middle class in developing countries the
current rate of food production will have to DOUBLE by 2050.
16000
U.N. High Estimate
15000
14000
13000
12000
11000
10000 U.N. Medium Estimate
Millions of people
9000 9 Billion People in 2050
8000
7 Billion
7000
6000 U.N. Low Estimate
5000
4000 We are here
3000
2000
1000
0
00 20 40 60 80 00 20 40 60 80 00 20 40 60 80 00
18 18 18 18 18 19 19 19 19 19 20 20 20 20 20 21
Estimated U.N. High U.N. Medium U.N. Low Actual
Figure 11. U.N. projections of human population growth to 2100.
178 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013Agriculture, plant physiology and humankind
potential croplands are what are termed “biodiversity predicted to become drier, which will affect agricultural
hotspots.” These biodiversity hotspots have already lost productivity. The melting of mountain glaciers would dry
70% of their original vegetation, yet they contain 50% of the up rivers, devastating irrigation-dependent agriculture
world’s plant species, which will disappear if we turn them around the world, affecting billions of people. Finally, high
all into farms. According to recent surveys, nearly 30% of all temperatures will also have numerous direct deleterious
plant species have not even been discovered yet, and among effects on crop growth, including increased evapo-
these yet-to-be-discovered species may be plants that could transpiration rates, decreased germination rates, inhibition of
hold the key to our survival in the future. We simply cannot photosynthesis, alteration of flowering times, inhibition
afford to destroy the last remaining biodiversity hotspots of sexual reproduction (especially pollen tube development),
on the planet. and an increase in plant diseases and herbivore attacks.
Another factor limiting our ability to increase the area of For every 1 degree Celsius rise in temperature, crop yields for
arable land for food crops is competition with biofuels. In the wheat and rice are expected to decline by 10% and maize and
United States, corn and cellulosic ethanol production are soybean yields are expected to decrease by 17%.
mandated to increase through 2025, and Brazil is planning That’s the bad news.
to expand sugar production for ethanol by 60% by 2019; so The good news is that plant biologists have never had
the total amount of land dedicated to biofuel production is such a stunning array of molecular tools at their disposal to
going to increase. This increase in arable land for biofuels tackle the twin challenges of population growth and climate
will be at the expense of croplands. Yet another factor change (Figure 13). Thanks to the rapid advances in DNA
preventing the expansion of farmland is the loss of arable sequencing, we now have an ever-expanding database of
land due to urban sprawl, soil salination from irrigation, and genomes, transcriptomes, expression profiles, small RNAs,
desertification from over-grazing. In summary, expanding and epigenomes. These DNA and RNA databases can be
farmland is not a viable option. Only by doubling crop correlated with proteomes, metabolomes, phenotypic data,
yields per hectare can we hope to feed nine billion people QTLs, and expression level QTLs, which can help us to infer
sustainably by 2050. gene function. With a better understanding of gene function,
But an even larger threat to agriculture looms on the we can potentially genetically engineer new traits into crops
horizon: global warming. If unchecked, climate change will that will not only increase their yields, but will enable them
pose big problems for agriculture in the future. The relentless to thrive even under the adverse conditions that may result
burning of fossil fuels is releasing billions of tons of CO2 from climate change, buying us needed time to stabilize the
into the atmosphere every year, triggering a cascade of population at a sustainable level.
by now familiar environmental consequences. First, CO2 Currently, the major commercialized genetically
accumulation is causing a rise in global temperature due modified crops involve relatively simple manipulations, such
to the greenhouse effect, anywhere from 2 to 6°C by the as the insertion of single genes for herbicide resistance or
end of the century. Rising temperatures will dry out forests pest-insect toxins.
leading to more forest fires, and forest fires release more The next decade will likely see the development of
CO2 to the atmosphere, raising the temperature still further. combinations of desirable traits and the introduction
The thawing of permafrost in the arctic region will release of new traits such as nutritional improvements, resistance
vast amounts of additional carbon into the atmosphere, to viruses and pests, drought tolerance, and salt tolerance.
raising the temperature once again. The melting of Arctic Between 10 and 20 years from now, the technology
ice will cause more sunlight to be absorbed by the ocean, for transforming with multiple genes will allow us to
raising its temperature even further. And if the ice sheets of introduce various polygenic traits into crops, such as
Greenland and Antarctica melt, sea level would increase by increasing nitrogen use efficiency and high temperature
67 m (220 ft). Even partial melting could raise the sea level tolerance. By mid-century, when the population will reach
enough to submerge coastal areas, reducing the amount of nine billion, we may have succeeded in creating nitrogen-
arable land still further. fixing cereals, perennial cereals, and crops with increased
Global warming will also affect rainfall patterns. Some photosynthetic efficiency.
areas may receive greater than average rainfall, while others It has long been a dream of humanity to improve
will receive less than normal rainfall. The subtropics are plants in various ways and make them more productive,
Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 179Lincoln Taiz
The Post-Mendelian Tool Kit for Increasing Crop Yields
Next Generation Sequencing
Genomes Transcriptomes Expression Profiles Small RNAs Epigenomes
Proteomes Metabolomes
Phenotypic Data QTLs and expression level QTLs
Gene Function
Genomic Resources for Crop Improvement
Figure 13. The new molecular tools available to increase crop yields per hectare, in the face of climate change.
attractive, or appealing. In the seventeenth century, Sir that we can now imagine. We have learned that they are
Francis Bacon, in his futuristic tract New Atlantis, made the as plastic in our hands as clay in the hands of the potter or
following predictions: colors on the artist’s canvas...
We have large and various orchards and gardens…And we Over the past 60 years, however, we have come to
make by art in the same orchards and gardens, trees and flowers appreciate that enhancements in agricultural productivity, by
to come earlier or later than their seasons; and to come up and whatever means, comes at an environmental cost. This means
bear more speedily than by their natural course they do. We we must use the new tools of molecular biology wisely — that
make them also by art greater much than their nature; and their is, sustainably — in order to reap the benefits. In the wise
fruit greater and sweeter and of differing taste, smell, colour, and words of prominent molecular biologist Nina Federoff (2004):
figure, from their nature. And many of them so we order, as they
become of medicinal use. Using our growing knowledge of plants and plant genes,
and our increasing skill at modifying them with molecular
The prolific American plant breeder Luther Burbank was techniques, we can make agriculture more focused and more
able to achieve many of the results that Bacon predicted. In a productive – if we are careful. The thoughtful choice of genetic
speech given in 1901, Burbank stated that: modifications can help us become better stewards of the earth.
The key words here are careful and thoughtful. Whether the
Botanists once thought their classified species were more technology will be helpful or harmful, in the long run, depends
fixed and unchangeable than anything in heaven or earth on how it is used, on the choices people make.
180 Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013Agriculture, plant physiology and humankind
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FASCIATED EAR2 locus. Nature Genetics 45:334-337.
Olmstead AL, Rhode PW (2008) Creating Abundance: Biological
Federoff N (2004) Mendel in the Kitchen. Washington, D.C.: Innovation and American Agricultural Development. Cambridge
University Press.
Joseph Henry Press.
Ray DK, Mueller ND, West PC, Foley JA (2013) Yield trends are
Evans LT (1998) Feeding the Ten Billion: Plants and Population insufficient to double global crop production by 2050. PLoS ONE.
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Theoretical and Experimental Plant Physiology, 25(3): 167-181, 2013 181You can also read
