A physiologist's perspective on plants and population: Feeding the Ten Billion: Plants and Population Growth L.T. Evans

Cambridge University Press, 1998. $54.95/£35.00 hbk, $19.95/£11.95 pbk (xiv + 247 pages)ISBN 0521 64081 4,ISBN 0 521 64685 5In 1798, when there were fewer than a billion people, Thomas Malthus issued his famous warning that arithmetic increases in food production could not keep pace with geometric population growth. Two hundred years later, plant physiologist Lloyd T. Evans has authored this book to commemorate Malthus's ‘Essay on the Principle of Population' and to consider whether the ‘Malthusian dilemma' still holds. The book is enjoyable reading and I recommend it to anyone interested in a refresher course on how plant research has interacted with population growth and how it might help to feed an even bigger world population. Evans examines the interactions between agricultural development and population growth from 10 000 years ago to the middle of the next century. Using fascinating vignettes, he describes the role of research, conducted by farmers, explorers and scientists, in enabling human numbers to reach today's 6 billion – a figure Malthus surely thought impossible. However, Evans points out that it is equally unclear how an expected population of 10 billion by 2050 are to be fed.Starting with a world of ∼5–15 million hunter-gatherers, the first five chapters review innovations made primarily by farmers that enabled the population to grow to a billion by 1825. Agriculture was born when people began replanting and cultivating plants that they had traditionally gathered. This generated a larger and more reliable food supply and opened the way to population growth, in turn generating greater demand for food. Evans reviews how rice-based agriculture in China and India, wheat in the fertile crescent of the Near East, and domestication of maize in Central America enabled local populations to increase many fold. As farmers intensified production they invented various crop rotations, employing fallows, legumes and animal manure to maintain soil fertility. Following the voyages of Columbus, explorers and botanists made key contributions by redistributing, testing and naturalizing crop plants around the world. Some of the ‘new' crops left their pests and diseases behind (at least for a while) and performed even better than in their original habitat. A few, including potato, required a period of adaptation to physiological factors, such as longer day length, and then became staple foods in their new locales. In the lowlands of Flanders and England, farmers introduced intensive management systems that combined rotations, new crops and water management. These farms were self-reliant in that they required few external inputs, yet they produced significant surpluses and represented an important shift from subsistence to commercial agriculture.In each of the next five chapters Evans relates how plant research contributed to an additional 1 billion increase in population. The second billion was added in slightly more than one hundred years (1825–1927) with science having a real impact at this time. Humphry Davy, Justus von Liebig and others ascertained the role of N, P and K and the fertilizer industry was born. The subsequent discovery of the role of bacteria in nitrogen fixation, photoperiodism in plants, essential trace nutrients and strategies of biocontrol, all contributed to increased production. The rediscovery of Mendel's laws of genetics brought clearer insight and somewhat greater predictability to the work of plant breeders.Feeding the third billion was achieved primarily through expansion of agriculture in developing countries and increasing use of cheap fertilizer, mechanization and pesticides in industrialized countries. Evans sees the 3 billion mark in 1960 as a turning point. By then, expansion in to new lands was roughly equaled by land being taken out of agriculture and there was a growing dependence on off-farm sources of energy and other industrial inputs. Beyond the 3 billion point there is no turning back to self-sufficiency in agriculture.The fourth and fifth billion were added in just 15 and 11 years, respectively, with most of the increase occurring in the developing countries. This rapid rate of population growth led to predictions of massive famines, but they were averted primarily because of the ‘green revolution'. First in Mexico and later in Asia, scientists used modern plant breeding techniques to develop broadly adapted semi-dwarf varieties of wheat and rice that respond to fertilizer by investing a greater proportion of their photosynthate in grain. Under irrigation, and with more intensive management practices, these varieties produced yields that were double, or triple (or even higher) their previous levels. Further breeding allowed their life-cycles to be shortened, enabling two and sometimes three crops to be grown in a year. Biotic and abiotic stress tolerance was also introduced, which allowed a greater proportion of the yield to be harvested.However, crop production in Africa remains a major challenge and I think Evans missed an opportunity to draw on his book's historical lessons to offer potential solutions. In Africa, fertilizer is not cheap, irrigation is not available and an Asian style green revolution is unlikely. To improve the productivity of Africa's rainfed agriculture, African farmers and scientists need to work together to develop the African equivalent of the two, three and four course rotations that were previously used to maintain soil fertility as agriculture intensified elsewhere. New crop varieties are also needed, each well adapted to one of Africa's diverse environments, to provide increased yield stability and reduced losses from pests, pathogens and variations in rainfall.In the past 12 years the population has grown to 6 billion. But there has also been good news. In Europe, agricultural production has continued to increase whereas the population has begun to decrease. With the exception of Africa, many developing countries have passed through a transition to replacement-level fertility rates. Demographers now project that the human population will stabilize at ∼10 billion.On the plant science side, advances in molecular biology are providing powerful new tools for agricultural research. And yet, as Evans correctly warns, 4 billion more people will need to be fed, 800 million currently remain undernourished and there are increasing environmental problems associated with high input agriculture. He and I agree that further research is clearly essential, and the public sector international agricultural research system is best positioned to address the challenges in Asia and Africa, where most of the increased production is, and will be, needed. Unfortunately, that system is now constrained by a lack of funds and a lack of technology. Too many economists, demographers and policy makers are simply assuming that increased food production can be taken for granted. This is not the case. Donor support for research must be revitalized and new institutional arrangements are needed to provide scientists in developing countries with access to the new technologies and genetic resources that are increasingly inaccessible because of various regulations and intellectual property rights. The challenge is formidable, but history has shown that the task is not impossible if the commitment is made.