by Christopher Gerry
figures by Kristen Seim

Summary: The human population has grown at a breakneck pace and threatens to further exacerbate a problem that has worsened in recent years: chronic hunger. Genetically modified crops could help to relieve this problem by providing increased yields and being more resistant to environmental stressors. In particular, the increasing prevalence of drought has prompted the development of crops that are more tolerant of high temperatures. These efforts, however, have afforded mixed results due to the genetic complexity of drought resistance and similar traits. Regardless, continuing to research this type of genetic engineering remains a promising strategy for feeding the world’s growing population.

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An Unsustainable Trend

If you’ve recently been feeling more claustrophobic than usual, you might want to blame your growing cohort of fellow humans. The world population has doubled over the past 50 years and continues to grow by roughly 100 million people each year (Figure 1). Even though the growth rate appears to be slowing, the population will likely continue to grow throughout the 21^st century and could reach 11 billion by 2100 [1]. This dramatic boom has evoked fears that our rapidly-growing population will surpass Earth’s inherent “carrying capacity” for humankind, echoing Thomas Malthus’ warnings from the late 18^th century. Thankfully, with regard to physical living space, these fears appear to be overblown; to reiterate a popular factoid, every human on the planet could live in a Texas-sized area that has the same population density as New York City [2].

Figure 1: 2015 UN Population Projections for the 21^st Century
The chart above illustrates previous world population trends and future probabilistic projections using data derived from the 2015 Revision of the World Population Prospects.  The current model projects an 80% likelihood that the population will reside within the dark band for any given year and a 95% likelihood that it will reside within either the light or dark band.  It’s typically more difficult to predict events that will take place further into the future, as illustrated by the widening of the bands over time.

Feeding that many people, on the other hand, is a much more difficult challenge. Roughly 800 million people remain undernourished despite the fact that the current output of the world’s farms could supply over 11 billion people with 2,000 calories per day [3]. As a result, more people die annually from chronic hunger than from HIV/AIDS, malaria, and tuberculosis combined [4]. Many of the world’s hungry live in developing countries, so increasing the food supply in impoverished regions would be an efficient way to ease suffering and save lives. A warming global climate, however, threatens to exacerbate local food shortages by increasing the frequency and duration of crop-crippling droughts. Even the most optimistic projections of population growth and climate change could represent potential catastrophe if we don’t improve our means of growing, harvesting, and distributing crops.

Farming 2.0

Modifying the genomes — the biological instruction manuals that dictate how organisms are assembled and maintained — of staple crops like rice, corn, and soybeans could relieve many of the pressures on the worldwide food supply. Recent advances in genome editing technology have allowed scientists to precisely add, delete, and rearrange pieces of genetic code to imbue crops with desirable characteristics (see this article). While it may sound like science fiction, large chemical companies like DuPont and Monsanto have been using this technology for over two decades on a wide variety of plants, many of which may alleviate world hunger. In 1994, Calgene introduced the first GM crop to be sold in the United States, the Flavr Savr tomato, which ripened slowly and had an extended shelf-life [5]. Flavr Savr tomatoes eventually disappeared from grocery stores because high production costs prevented them from becoming profitable, but lengthening the amount of time that produce stays fresh may be used to increase the food supply in underdeveloped areas.

Figure 2: A Common Misconception Regarding the Production of GM Crops
Despite what you may see on the Internet, GM crops are not prepared by injecting them with mysterious fluorescent solutions.  In reality, genetic engineering is a much less dramatic process that often involves pipetting clear, colorless liquids into other clear, colorless liquids.

A more direct solution to chronic hunger involves GM crops that have been engineered to increase yield, which is a measure of the amount of food that may be harvested from a given area of land. A popular strategy that scientists use to increase this metric is to insert a gene that confers resistance to commonly used weedkillers. Farmers that adopt these herbicide-resistant crops are able to clear their fields of unwanted plants without tilling the soil, which allows them to plant higher densities of crops. Geneticists have also developed pest-resistant crops that are poisonous to hungry insects, greatly reducing farmers’ reliance on chemical pesticides. Lastly, genetic engineering can generate crops that are resistant to microbial infections, such as the potato blight that triggered the Irish Potato Famine in the mid-19^th century [6].

How these scientific ideas actually translate to the fields is often the subject of intense debate, but a recent review of almost 150 studies has concluded that GM technology has significantly increased crop yields and farmer profits over the past 20 years. GM soybeans, maize, and cotton were associated with a 22% overall increase in yield, 37% decrease in pesticide use, and 68% increase in farmer profits, despite the higher cost of GM seeds (Figure 3) [7]. Furthermore, farmers in developing countries experienced yield and profit gains that were 14% and 60% higher, respectively, than those observed by their counterparts in industrialized countries. This is particularly encouraging because food shortages often take their most severe toll in underdeveloped regions. Even with these new crops, however, some areas of the world have seen their agricultural output begin to plateau [8]. Therefore, increases in yield alone will likely not be able to sustain our ever-growing populace.

Figure 3: Overall Effects of Farming with GM Crops
The graph above shows the average percentage differences in several important metrics that result from farmers adopting GM crops.  Overall, GM crops were associated with substantially higher yields and lower pesticide use.  The slight increase in total production costs is likely attributable to the increased price of GM seeds, but it is dwarfed by the dramatic increase in farmer profits.  Data obtained from Klumper and Qaim [8].

Trial by Fire

Another strategy that genetic engineers are currently pursuing is the development of drought-resistant crops. As the climate steadily warms, droughts are projected to occur more frequently and to last longer, threatening harvests worldwide. In fact, the drought that’s been wringing California dry for almost four years is the worst that the Golden State has seen in over a century [9]. Additionally, a drought-mediated contraction in the food supply would likely result in higher prices and, thus, further lower the amount of food that’s accessible to the world’s poor. Farmers could hedge against these potential losses by planting GM crops that can flourish in both wet and arid conditions. African farmers, in particular, may be able to use these crops to exploit previously untapped agricultural opportunities. By doing so, these crops could also increase the food supply in one of the world’s most malnourished areas.

Unfortunately, current GM drought-resistant crops typically fare no better in dry conditions than do drought-resistant crops that have been developed via “conventional” genetic engineering — selective breeding. Just as human height and intelligence are influenced by a poorly understood interplay of many different genes and environmental factors, complex traits like drought resistance are typically determined by more than one or two pieces of genetic code. Present-day research has not precisely identified the intricate combination of genes that allows crops to thrive in arid conditions, so these crops have likely not yet reached their full potential.

Plummeting research costs, however, will likely allow genetic engineers to modify more complex traits in the years to come. The current cost of determining the sequence of your genetic code is roughly five thousand dollars, which is only 0.05% of the ten million dollars you would have had to pay 8 years ago (Figure 4) [10]. Lower research costs likely will lead to an expansion of our molecular toolkit for combating hunger as we draw connections between traits and specific genes, such as those that successfully confer drought resistance to selectively bred crops.

Figure 4: The Cost to Sequence a Human Genome has Fallen Precipitously
The cost of sequencing an entire human genome has fallen so dramatically over the past few years that it has outpaced Moore’s law of computing – note the logarithmic scale on the Y-axis.  Moore’s law states that technology advances at such a rate that the maximum number of transistors in a microchip (and, thus, computing power) doubles every two years.  Genome sequencing costs aligned well with Moore’s law’s projection from 2001-2007, but advances in genome sequencing technology that were introduced in 2008 have left Moore’s law in the dust.  Data obtained from the National Human Genome Research Institute.

One such innovation that has already come to fruition is a new rice plant that was described just last month in the journal Nature. This new strain contains an additional gene that transfers growth away from the roots and towards the parts of the plant that humans can actually eat. The resulting GM rice produces 43% more grain and emits up to 97% less methane than conventional rice does. Methane is a powerful greenhouse gas (roughly 84 times more potent than carbon dioxide), so this rice should not aggravate the environmental problems that other GM crops are trying to solve. In fact, rice paddies are responsible for up to 17% of global methane emissions, so widespread adoption of this strain would be a boon for both our stomachs and our environment [11]. Unfortunately, it won’t be available to farmers until 10 to 20 years from now, but field trials have largely been encouraging.

Other promising GM crops of the not-so-distant future include flood-resistant rice, maize that can grow in nitrogen-poor soil, and potatoes that can immunize consumers against hepatitis B infection [12]. Some of these ideas remain science fiction for the moment, but overwhelming evidence has already shown that changing food on the molecular level can help to solve some of the world’s biggest problems.

Christopher Gerry is a first-year graduate student in the Department of Chemistry and Chemical Biology at Harvard University. He is currently studying the science of therapeutics in Stuart Schreiber’s lab.

This article is part of the August 2015 Special Edition, Genetically Modified Organisms and Our Food.

References

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