Botkin Environmental Science Earth as Living Planet 8th txtbk

11.7 Genetically Modified Food: Biotechnology, Farming, and Environment 229
standing, and the widespread use of genetically modified
crops (GMCs) is under way before the environmental effects
are well understood. The challenge for environmental
science is to gain an understanding of environmental
effects of GMCs quickly.
New Hybrids
The development of hybrids within a species is a natural
phenomenon, and the development of hybrids of major
crops, especially of small grains, has been a major factor
in the great increase in productivity of 20th-century agriculture.
So, strictly from an environmental perspective,
genetic engineering to develop hybrids within a species is
likely to be as benign as the development of agricultural
hybrids has been with conventional methods.
There is an important caveat, however. Some people
are concerned that the great efficiency of genetic modification
methods may produce “superhybrids” that are so
productive they can grow where they are not wanted and
become pests. There is also concern that some of the new
hybrid characteristics could be transferred by interbreeding
with closely related weeds. This could inadvertently
create a “superweed” whose growth, persistence, and resistance
to pesticides would make it difficult to control. Another
environmental concern is that new hybrids might
be developed that could grow on more and more marginal
lands. Raising crops on such marginal lands might
increase erosion and sedimentation and lead to decreased
biological diversity in specific biomes. Still another potential
problem is that “superhybrids” might require
much more fertilizer, pesticide, and water. This could
lead to greater pollution and the need for more irrigation.
On the positive side, genetic engineering could lead
to hybrids that require less fertilizer, pesticide, and water.
For example, right now only legumes (peas and their relatives)
have symbiotic relationships with bacteria and fungi
that allow them to fix nitrogen. Attempts are under way to
transfer this capability to other crops, so that more kinds
of crops would enrich the soil with nitrogen and require
much less external application of nitrogen fertilizer.
The Terminator Gene
The terminator gene makes seeds from a crop sterile. This
is done for environmental and economic reasons. In theory,
it prevents a genetically modified crop from spreading. It
also protects the market for the corporation that developed
it: Farmers cannot avoid purchasing seeds by using some of
their crops’ hybrid seeds the next year. But this poses social
and political problems. Farmers in less-developed nations,
and governments of nations that lack genetic-engineering
capabilities, are concerned that the terminator gene will allow
the United States and a few of its major corporations
to control the world food supply. Concerned observers
believe that farmers in poor nations must be able to grow
next year’s crops from their own seeds because they cannot
afford to buy new seeds every year. This is not directly an
environmental problem, but it can become an environmental
problem indirectly by affecting total world food production,
which then affects the human population and how
land is used in areas that have been in agriculture.
Transfer of Genes from One Major
Form of Life to Another
Most environmental concerns have to do with the third
kind of genetic modification of crops: the transfer of genes
from one major kind of life to another. This is a novel effect
and, as we have explained, therefore more likely to have undesirable
results. In several cases, in fact, this type of genetic
modification has affected the environment in unforeseen
and undesirable ways. Perhaps the best-known involves potatoes
and corn, caterpillars that eat these crops, a disease
of caterpillars that controls these pests, and an endangered
species, monarch butterflies. Here is what happened.
As discussed earlier, the bacterium Bacillus thuringiensis
is a successful pesticide that causes a disease in many caterpillars.
With the development of biotechnology, agricultural
scientists studied the bacteria and discovered the
toxic chemical and the gene that caused its production
within the bacteria. This gene was then transferred to potatoes
and corn so that the biologically engineered plants
produced their own pesticide. At first, this was believed
to be a constructive step in pest control because it was no
longer necessary to spray a pesticide. However, the genetically
engineered potatoes and corn produced the toxic BT
substance in every cell—not just in the leaves that the caterpillars
ate, but also in the potatoes and corn sold as food,
in the flowers, and in the pollen. This has a potential, not
yet demonstrated, to create problems for species that are
not intended targets of the BT (Figure 11.20).
A strain of rice has been developed that produces betacarotene,
important in human nutrition. The rice thus has
added nutritional benefits that are particularly valuable for
the poor of the world who depend on rice as a primary food.
The gene that enables rice to make beta-carotene comes
from daffodils, but the modification actually required the
introduction of four specific genes and would likely be
impossible without genetic-engineering techniques. That
is, genes were transferred between plants that would not
exchange genes in nature. Once again, the rule of natural
change suggests that we should monitor such actions carefully.
Indeed, although the genetically modified rice appears
to have beneficial effects, the government of India has refused
to allow it to be grown in that country. 15
There is much concern worldwide about the political,
social, and environmental effects of genetic modification
of crops. This is a story in process, one that will change
rapidly in the next few years. You can check on these fastmoving
events on the textbook’s Web site.