Plant Resources for Human Development: Time for a Renewed

Plant Resources for Human Development: Time for a New Relationship?
Peter A. Jolliffe
Agroecology Program
Faculty of Land and Food Systems
University of British Columbia
Vancouver, BC V6T 1Z4
Summary: The long relationship between humans and plants has mutually affected both
partners. Our primate predecessors mainly existed as vegetarian tree-dwellers.
Conditioned by this, primates evolved several key traits, including the ability to grasp and
manipulate objects and excellent vision. Through much of its several million years of
existence the genus Homo survived as a hunter-gatherer, with plants being a normal part
of the diet. The post-glacial agricultural revolution, involving the domestication of plant
crops, supported the development of the first Neolithic cities. This eventually led to other
technologies, more complex societies and civilization. Humans presently exploit many
plant species in diverse ways: for fibre, building materials, pharmaceuticals and
aesthetics. We should not, however, underestimate key the role of plants as food. They
presently contribute more than 90% of the dry matter in food consumed by humans. And,
through their primary production, they support the functioning of global ecosystems upon
which we ultimately depend. Two strategies have largely been responsible for increases in
agricultural production during the past two centuries: (1) expanding the area of cultivated
land, and (2) increasing food output per land area by intensification of inputs. Looking to
the future, human population increase will drive increased demand for food, and these
strategies will be less effective than they have been up to now. It seems essential,
therefore, that humans re-think their connections with plants, and work to establish a new
and more sustainable partnership.
Almost exactly 40 years ago I was fortunate to attend a paper given by noted cosmologist Carl
Sagan, delivered at meetings of the American Association for the Advancement of Science in
San Francisco in December 1965. At the time, Sagan was working to prepare for the first space
missions to Mars, and he was concerned with the problem of how to detect the existence of life
on other planets. The title of his paper, however, was “Is There Life on Earth?” Creatively,
Sagan had inverted the problem and wondered whether satellite-based imagery, using
technologies available at that time, would definitively prove that Earth supports intelligent life.
This was only 8 years after Sputnik, and remote sensing was primitive by today’s standards.
Indeed, after analyzing the available satellite images of Earth, Sagan concluded that those data
alone were insufficient to prove the existence of intelligent life on Earth. The best evidence he
could find was from images of clear-cut areas in the Canadian boreal forest: patches of snowfall
on logged areas stood out as regular white tiles against the darker background of the surrounding
forest. As always, Sagan was a compelling speaker and I found it striking that, looking from
space, the clearest indication of human presence on Earth at that time was offered by our
influence on vegetation.
Here, I will give an overview of some of the main relationships that have existed between
humans and plants, from our primate ancestors to the present day. Within the space available, a
comprehensive treatment of the many links between plant resources and human development is
not possible. Instead, I will sketch some broad perspectives on these relationships, reflecting on
humans, food and agriculture. In doing this I will emphasize how our relationships with plant
resources have changed, and how those changes have operated to transform both ourselves and
the plant species that we depend upon.
Ancient Ancestors
Anthropologists have broadly delineated the evolutionary sequence leading from early primates
to Homo. We descend from arboreal quadrupeds which mainly lived as vegetarians. This is
evident in our digestive systems and in the structure of our teeth and facial muscles, well adapted
to masticate and process plant food. Our hands, being adapted for tree-climbing, are wellstructured for grasping and manipulation, and our binocular colour vision is highly effective in
distinguishing objects in dense vegetation. Clearly, through our primate lineage, we have been
partly sculpted by our ancient relationships with plants.
Insights into our early relationships with plants are offered by observations of our closest
relatives today, the bonobo (Pan paniscus) and chimpanzee (P. troglodytes). Both species have
highly diversified diets, being primarily frugivorous but also consuming leaves, flowers, and pith
(Rafert & Vineberg 1997; Newton-Fisher 1999). Both species have colour vision, and by their
behaviour they are known share with us a high ability to distinguish aromas and flavours
associated with palatable and nutritional dietary sources. Field observations on bonobo in the
Congo basin found that it exploits over 110 species of plants as food sources, although more than
80% of their diets came from less than 10 plant species, especially fruit of Dalium (Rafert &
Vineberg 1997). Chimpanzees spend about 7 hours a day feeding, much of that time in trees. At
Budongo Forest Reserve in Uganda, for example, ground-level herbaceous vegetation was little
used for food, and chimpanzee diet was dominated by arboreal fruit of four plant species and
leaves of two species. Figs were considered to be the staple diet, being consumed through most
of the year (Newton-Fisher 1999).
There is a small non-plant component in the diets of both bonobo and chimpanzee. For
bonobo this is mainly invertebrates with possibly some freshwater shrimp or fish. Chimpanzees
also prey upon young baboons and monkeys (Rafert & Vineberg 1997). Pioneering observations
by Jane Goodall at Gombe National Park in Tanzania revealed that chimpanzees exploit plant
tools in feeding on termites. More recent studies (Sanz et al. 2004) have found that reusable
wooden tools are regularly employed by chimpanzees to extract termites from aboveground and
subterranean nests. Their tool forms are specialized for different tasks, and tool assemblages
differed between different communities of chimpanzees. It is not known for certain whether our
common ancestors shared all of these attributes, but collectively the evidence suggests ancient
and fundamental connections between plants, human physique, tools and the origins of culture
(Balick & Cox 1996).
The Post-glacial Agricultural Revolution
For much of their several million years of history, members of the genus Homo existed as
scavengers and as hunter-gatherers. Their stone and bone tools indicate that meat was an
important part of their diet, and like more modern Inuit peoples, big game hunters such as Cro
Magnon may have used plants as a secondary source of food. However, patterns of dental wear
confirm that even for the big game hunters plants remained as a staple part of the human diet,
and the important use of plant materials for fire during glacial periods is not to be discounted.
During the several thousand years following the last glacial retreat, humans in several
parts of the world independently underwent a revolutionary transition from hunter-gatherers to
agricultural societies. Changes big game abundance associated with post-glacial climate change
may have pressured people to undertake cultivation (Pringle 1998). The transitions to agriculture
were gradual, and the timelines and details are not fully understood (Pringle 1998). They are best
documented for the Near East where by 9000 BP Jericho was established as a small settlement,
and where Catal Huyuk emerged in Anatolia as the first known city by 8000 BP. Numerous
religious sites have been found within Catal Huyuk, and there has been some speculation about
role of psychedelic plants in the development of religion there. Syrian rue containing the
compounds harmine and harmaline grows abundantly at the Catal Huyuk site, and Amanita
mushroom, ergotized rye and cannabis are common in the area.
The domestication of animals may have shortly preceded plant domestication and served
as a bridge to settlements and to plant cropping systems. Although the dog had been
domesticated before the end of the last ice age, sheep were the first food animal domesticated.
This had occurred at least by 10,000 BP in the Near East (present day Iran, Iraq, Turkey),
followed in less than a thousand years by goats. The maintenance of sheep or goats leads people
to identify with grazing territory; it reduces the need to be nomadic and is conducive to
settlement. With settlements, humans can tend crops. There is some evidence for cultivated rye
production as early as 13,000 BP in the Near East (Pringle 1998), and evidence for domesticated
barley dates back to 10,200 BP in present-day Israel (Evans, 1993). In Mesoamerica, there is
evidence for domesticated Cucurbita pepo from as early as 10,700 BP, although extensive
adoption of agricultural cultivation did not occur rapidly in the western hemisphere. Other early
centres of plant domestication were in present day Thailand (Piper, Ricinus) and China (broomcorn millet, rice), all before 8000 BP (Evans 1993; Hancock 2004). There was also yam
cultivation by that time in sub-Saharan Africa, and most of our major crops had been
domesticated by 5000 BP (Hancock 2004).
The centres of plant domestication were invariably centres of settlement, and while we
don’t understand the full process there is little disagreement with the idea that these changes in
the way humans related to plants were fundamental steps toward the development of advanced
human societies and cultures. It is also clear that the process of domestication resulted in rapid
genetic change in the plant species involved (Hancock 2004). Therefore, the post-glacial
agricultural revolution not only changed people, it also altered the plants they were exploiting.
Also, as agriculture developed humans did not discontinue using wild plant species,
which has continued to the present (Balick & Cox 1996). For example, an ethnobotanical survey
of plant use by extant Native American peoples documented the use of 4029 species and 44,691
usages (Moerman 1998). More than half of those uses were medicinal, and in addition to food
plants were also used for fibres, dyes, ornaments, shelter, cleaning agents, fertilizers, incense,
fragrance, insecticides, lubricants, musical instruments, preservatives, soap, smoking, snuff and
weapons. Clearly, the connections between humans and plants are extensive and profound.
The Present
Over the past several centuries there have been immense changes in human societies and
populations. In part, this has been enabled by the radical expansion and intensification of
agriculture. Once again, humans have been revolutionizing their relationships with plants, with
important consequences to human development.
An important contributor to this has been human exploration and travel. Disparate and
distant cultures have been brought into contact, enabling crops to flow from their early centres of
distribution to other areas throughout the world. The globalization of our major crops has led to
many interesting results. For example the tomato, native to the Pacific coast of South America, is
now a characteristic ingredient of Italian cuisine. The United States has become the world’s
major rice exporter. The diversification of food crops available throughout the world has helped
with human dietary balance and is important for our food security.
Another major contributor to food increase has been through scientific advancement. It
would take considerable time to document this in any detail, but science has affected agriculture
comprehensively in key areas of plant genetics and breeding, nutrient management, irrigation
and stress tolerance, pest and disease control, and post-harvest handling and storage. By the late
1960s, the determinants of crop performance were sufficiently well understood that physiologists
were able to provide plant breeders with recipes for high-yielding attributes in cereals, which
were the basis for the ‘green revolution’ in rice (Matsushima 1970; Yoshida 1972). As before,
human activities have affected the plants around us. An example of this is the development of
weed resistance to the herbicides atrazine and simazine following extensive use of these
chemicals on crops for weed control. A broader example is the observation that stomatal
densities have decreased in a number of plant species as atmospheric carbon dioxide levels have
risen over the past several centuries (Woodward 1987).
Agriculture is inherently a land area-based operation, and the expansion of land area
devoted to agriculture is thought to be one of the two most important causes of increasing global
food production during recent centuries (Evans 1993). Exploration and migration by peoples has
led to the expansion of agriculture into regions where cultivation was not extensively practiced
before, such as North American prairie. The diversification of crops available to farmers,
together with the development of hardy types and techniques for growing crops in formerly
unsuitable regions, have also increased the potential land area useable for food production. At
present, however, the extent of arable land suitable for agriculture is not increasing significantly.
Indeed, it may even be declining due to a set of largely human-related activities that either divert
arable land for other purposes, or erode the agricultural capabilities of that land: e.g. salinization,
desertification, laterization, urbanization, and industrialization.
The second main driver of recent food increase has been intensification of agriculture,
resulting in higher food outputs per unit land area. Maximum crop yields increased impressively
with the advent of chemical fertilizer use, such as phosphate fertilizers through the work of
Lawes and Gilbert in Britain in the 1840s, and through the intensive use of nitrogen- and
potassium-containing fertilizers since the early 20th century. Mechanization has been part of the
intensification of agriculture, not only for cultivation, chemical applications and harvesting, but
also for irrigation, transport and storage.
Intensive agriculture is hallmarked not only by high levels of production but also by a
narrowing of the genetic base. Low biodiversity in intensive agriculture is helpful for
mechanization and has several causes: elimination of species through weed and pest control, and
by the use of monocultures of a limited number of genotypes. Mechanization has led to a decline
in human labour per unit land area, and the reduction in opportunities to work in agriculture is
partly responsible for the migration of people from rural to urban areas.
These changes have led to a disconnect between many humans and the plants they
depend upon. It is paradoxical that although we know more about plants today than ever before,
they are often less present our everyday lives than was the case in earlier societies. Overall,
humans now use thousands of plant species, but I know from talking with my students that many
people do not appreciate how much we rely on only a few dozen plant species for most of our
food needs. In terms of food, cereal crops are of paramount importance. Just three cereal crops
(wheat, rice, maize) supply about half of the world’s food, and collectively cereals constitute
about 2/3 of the total (Evans 1993). On a dry matter basis, animals and fish supply less than 10%
of the total, although they are the source of about 18% of dietary protein (Evans 1993).
The Near Future
So, like our primate ancestors, plants remain our predominant source of food. In the rest
of this article I will focus on the sustainability of human food supply, although human impacts
on forest systems are another major concern (Williams 2003).
There is cause to believe that the main strategies we have been using to increase global
food production, ‘farm more land’ and ‘intensify by providing higher resource inputs’, may be
losing their potential. As mentioned earlier, arable land is being lost due to a number of
processes, so prospects for continuing this strategy for agricultural expansion are therefore
diminishing. Some suggest that humans should overcome the terrestrial limitations to food
production by farming the oceans. I worry about relying on this option for at least two reasons:
effective technologies for extensive open-ocean farming either don’t exist, or their widespread
use may lead to adverse ecological consequences in systems where human over-exploitation of
fisheries has already been detrimental (Jenkins 2003).
Perhaps there is more latitude for expanding food production through further agricultural
intensification. After all, much existing arable land is not being used to full capacity. However,
this strategy is eventually limited by the pattern of resource-dependence of plant production
systems. This has the same form as the ‘diminishing returns’ pattern in economics where
stepping up inputs successively results in less and less improvement as the total level of inputs
rises. So, if we double fertilizer inputs once again we will not get nearly the same boost in yield
as we achieved through the previous doubling. Average crop yields have improved in many
crops during the past generation, but not in all cases. For example, long-term surveys of
horticultural crop yields in southern Canada show increases until the mid-1980s, followed by
yield declines and/or greater variability (McKeown et al. 2005). Maximum achievable yields in
many major crops do not seem to have changed very much in the past 30 years, despite a
considerable advancement in biological science during that time.
It is not my purpose to discredit intensive agriculture and the benefits that can be through
its use. However, it should be recognized that there are risks attendant upon increasing
agricultural intensification and expansion. These includes the requirement for higher energy
inputs into agriculture, involving additional fossil fuel use, higher energy costs, depletion of nonrenewable resources and added greenhouse gas emissions. Ecological principles suggest that, due
to low biodiversity, intensive crop monocultures are inherently less stable than more diverse
systems (Gliessman 1998). The high risk associated with extensive planting of a few genotypes
was exemplified by the Southern corn leaf blight disaster in 1970-71 (Ullstrup 1972). A new race
of Helminthosporium maydis (syn. Cochliobolis heterostrophus) attacked corn inbreds and
hybrids that possessed Texas male-sterile cytoplasm, which was more than 80% of the dent corn
grown in the U.S.A. at that time. Massive crop losses occurred, amounting to 250 million bushels
of corn in the state of Illinois alone. Intensive cropping systems are not closed nutrient cycles. In
consequence, high inputs of fertilizers are followed by high outputs to surrounding ecosystems,
disturbing their functioning and composition. If humanity simply operates to appropriate an
increasing fraction of planetary environmental and biological resources, it inevitably acts to
disturb natural ecological balances and ecosystem services that are fundamental to our survival.
Beyond the biological risks, the shift from low- to high-input agriculture can have negative
socio-economic consequences, being disruptive to local economies and traditional farming
At the start of this discussion I mentioned Carl Sagan’s talk in 1965. When he made that
presentation the world had about 3.5 billion human inhabitants, and atmospheric carbon dioxide
concentrations were less than 320 parts per million. Now there are about 6.5 billion people, and
carbon dioxide levels are near 380 parts per million and continuing to increase steadily because
of human activities. Current estimates are that about 860 million people on Earth suffer from
significant dietary malnutrition. Forecasts project a slowing in the rate of human population
increase over the next generation, with global population reaching about 9 billion people in the
year 2050 (Cohen 2003). In the five weeks since I was asked to write this article, the total
number of people on Earth has increased by about one-quarter of the present population of
It seems to me that, while these trends are well known, we have nevertheless become
complacent about our abilities to cope with them. We see regular evidence that convinces us of
the power of science and the rapid advancement of technology. It is easy to conclude that surely,
if future difficulties in food sustainability come to pass, we ought to be able deal with such
problems through the power of science and the invention of new technologies.
I would agree that prospects are good for many helpful advances in science and
technology. However, for reasons suggested above I suggest that we cannot simply assume our
past approaches to agricultural development can simply be extended into the future in order to
meet increasing human food needs. In my opinion, humanity is about to take a gamble that in the
next generation, as human populations increase by about 50%, new approaches will be invented
that will generate major increases in food supply without causing ecological havoc. And, it is
gambling that the new approaches will arrive in a timely way, avoiding widespread human
Some agricultural scientists I know are not overly concerned about our prospects for
increasing food production in the near future. Since the year 2000, however, I have attended a
number of (>10) seminars and discussion groups where reputable agricultural scientists have
publicly expressed doubt that today’s agriculture is sustainable. These were all people with
extensive international experience - about half of them being department heads or senior
administrators at academic institutions. They included scientists from Denmark, Britain, the
Netherlands, the United States, Chile, Australia and Canada, and their skepticism about
agricultural sustainability was for many different reasons. They expressed concerns about:
impacts of climate change, rising costs of energy and other agricultural inputs, degradation and
alienation of agricultural land, disruption due to due to political and social change, vulnerability
to disease and pests, the loss of traditional knowledge, demographic change, and the poor ability
of agriculture to recruit young farmers. This is a long list, but it is interesting to reflect that few
of these concerns are addressable through narrow scientific approaches.
This may all seem rather gloomy, but on balance I am optimistic about what can be done
to meet these challenges if humans work collectively toward a common goal. At the heart of this
issue is the development of an ethical framework that has long-term sustainability and the wellbeing of humans and nature as its goal. Matters of future food supply might first appear to be the
‘problem’. But, in my view it is more accurate to recognize that we are being confronted by
problems of human behaviour. We need to find ways to address modes of human behaviour that
act contrary to a sustainable future.
Plants are, as they always have been, a fundamental part of this. As human development
proceeds we should not lose track of the knowledge base associated with the farming practices of
indigenous peoples (Gliessman 1998), which have often been sustained for hundreds or even
thousands of years. Although even in those cases there is no assurance that scaling-up such
practices for the expansion of food production would not lead to some of the same difficulties we
have encountered with intensive farming. I am optimistic about the future because in the past
humans have demonstrated a considerable ability to adapt. In working toward sustainability, it
seems that we will again have to reinvent how we interact with plants, how we exploit them, and
how we sustain them.
I thank Dr. Quazi Abdul Fattah, Professor at Dhaka University and my friend for almost 40
years, for inviting me to prepare this article. I thank my colleague Dr. A. R. Reisman for helpful
comments on a draft of this paper.
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Evans, L.T. 1993. Crop Evolution, Adaptation and Yield. Cambridge University Press.
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