Where Does Nature's Wisdom Lie?
|February 1, 2012|
Wild rice growing near the headwaters of the Mississippi River.
by R. Ford Denison
Though Charles Darwin was suitably impressed by what contemporary plant and animal breeders had accomplished, simply by selecting which individuals get to reproduce, he also noted that similar processes occur in nature, with selection imposed by weather, predators or competition, which has been going on, worldwide, for millions of years. With plant breeders working with much smaller land areas, over much shorter times, he wrote, “Natural Selection… is as immeasurably superior to man’s feeble efforts, as the works of Nature are to those of Art.”
Consider wild rice, shown above growing near the headwaters of the Mississippi River. Natural selection has been improving this species, by evolution’s criteria, for millions of years. Better-adapted plants (those best at extracting nutrients from flooded soils, defending themselves against pests and pathogens, and producing seeds in warm and cold years, in deep or shallow water), had more surviving offspring. Their descendants inherited those adaptations. So plant breeders developing new rice varieties (especially for farmers who can’t afford fertilizer or control water depths) might learn something useful from research on how wild rice faces similar challenges.
What about nature’s “lies”? Notice that wild rice grows naturally almost as a monoculture, not mixed with other plant species. Tropical forests, on the other hand, have much greater species diversity. Can we conclude that aquatic plants, like rice or taro, should be grown as monocultures, while tree crops should be grown as diverse mixtures of species? Or maybe cold climate crops should be grown as monocultures (many northern forests aren’t very diverse either), while tropical crops should be grown as mixtures.
These hypotheses implicitly assume that natural selection, or other natural processes, have improved the overall organization of natural plant communities, not just the individual species that live there. Most evolutionary biologists, however, tell us that natural selection is much better at improving trees than forests. This is especially true when the interests of individuals conflict with those of the community as a whole. A more diverse forest might be less susceptible to disease outbreaks, but that won’t stop individual redwood trees from growing taller and shading out competitors of other species. Similarly, the low diversity of wild rice stands doesn’t prove that more diverse plant communities wouldn’t be more productive, more efficient in the use of scarce resources, or more sustainable over decades.
The species composition of plant communities depends on short-term ecological processes as well as longer-term evolutionary ones. Have these ecological processes somehow been improved over millennia, as individual-plant adaptations have? If so, then information about the overall organization of natural plant and animal communities might be just as useful for designing agricultural landscapes as the adaptations of individual wild species can be in guiding the improvement of individual crops. Natural selection’s innovations do seem like a great source of ideas to improve agriculture.
My recent book, Darwinian Agriculture: How Understanding Evolution Can Improve Agriculture, asks where nature’s wisdom is to be found, but also whether nature can “lie” to us. In particular, can we mislead ourselves, when we try to apply ideas from nature to agriculture? I conclude, tentatively, that the overall organization of natural forests has not been improved as consistently, by any natural process, as the individual adaptations of wild species have been improved by natural selection. Therefore, it is probably safer to copy trees than forests. The available data aren’t entirely conclusive, however. Furthermore, natural communities and landscapes provide essential context for understanding the sophisticated adaptations of wild species. To predict whether something that works well in a forest will also work well in an orchard, we need a deeper understanding of both forests and orchards.
As well, biotechnology’s many promises will not be fulfilled anytime soon. Most of the “improvements” proposed by biotechnology have already been tested by natural selection, and rejected. For example, increasing the expression of a gene for “drought tolerance”? Tried and tested, but plants were less competitive under non-drought conditions. Turning chemical defenses against insect pests on all the time, even when pests are scarce? Tried also, but it scared away pollinators. The list continues.
Sometimes however, traits that were rejected by past natural selection may be just what we want. Berries without thorns are an obvious example. Natural selection favors traits that enhance individual competitiveness, whatever the consequences for the community as a whole. We humans however, can select for traits that natural selection would reject, including individually costly traits that improve cooperation between species, such as legume crops and the symbiotic bacteria that provide them with nitrogen.
Past natural selection, based on competition among plants, gave crops more efficient photosynthesis than anything biotechnologists could design, but it also gave them a tendency to over-invest in stems (to compete for light) at the expense of grain. Sometimes, it would seem that an evolutionary perspective on agriculture calls for reversing the effects of past evolution.
About the Author:
R. Ford Denison is an evolutionary biologist and Professor at the Univeristy of Minnesota.
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