Genetic diversity

Genetic diversity includes the inherited traits encoded in the deoxyribonucleic acid (DNA) of all living organisms and can be examined on four levels: among species, among populations, within populations, and within individuals. Populations with higher levels of diversity are better able to adapt to changes in the environment, are more resistant to the deleterious effects of inbreeding, and provide more opportunities for animal and plant breeders to cultivate types or varieties with qualities desired by humans.

Background

Genetic diversity is the most fundamental level of biological diversity because genetic material is responsible for the variety of life. For new species to form, genetic material must change. Changes in the inherited properties of populations occur deterministically through gene flow—mating between individual organisms representing formerly separated populations—and through natural or artificial selection, which occurs when some types of individuals breed more successfully than others. Change can also occur randomly through mutations or genetic drift when the relative proportions of genes change by chance in small populations. Populations with higher levels of diversity tend to do better—to have more survival options—as surroundings change than do populations—particularly smaller ones—with lower levels of genetic diversity.

Preservation Efforts

Conservation efforts directed at maintaining genetic diversity involve both germplasm preservation—germplasm kept in a steady state for periods of time—and germplasm conservation—germplasm kept in a natural, evolving state. The former usually involves ex situ laboratory techniques in which genetic resources are removed from their natural habitats. They include seminatural strategies such as botanical gardens, arboretums, nurseries, zoos, farms, aquariums, and captive fisheries as well as completely artificial methods such as seed reserves or “banks,” microbial cultures—preserving bacteria, fungi, viruses, and other microorganisms—and tissue cultures of parts of plants and animals, including sperm storage, and gene libraries, involving storage and replication of partial segments of plant or animal DNA.

Conservation areas are the preferred in situ—at the natural or original place—means of protecting genetic resources. Ideally these include preserving the number and relative proportions of species and the genetic diversity they represent, the physical features of the habitat, and all ecosystem processes. It is not always enough, however, to maintain the ecosystem that the threatened species inhabits. It is sometimes necessary to take an active interventionist position in order to save a species. Controversial strategies can include the reintroduction of captive species into the wild, sometimes after they have been genetically manipulated. Direct management of the ecosystem may also be attempted either by lessening human exploitation and interference or by reducing the number of natural predators or competitors. However, management of a specific conservation area varies in terms of what is valued and how preservation is accomplished.

Crop Diversity

One area of keen interest that illustrates the issues involved with the preservation of any kind of genetic diversity is how to preserve crop germplasm. Largely conserved in gene banks, crop germplasm was historically protected by farmers who selected for success in differing environments and other useful traits. Traditionally cultivated varieties (landraces) diversified as people spread into new areas. Colonial expansion produced new varieties as farmers adapted to new conditions and previously separated plant species interbred; other species were lost when some societies declined and disappeared.

By the early 1900s, field botanists and agronomists were expressing concern about the rapidly escalating loss of traditionally cultivated varieties. This loss accelerated after the 1940s as high-yielding hybrids of cereal and vegetable crops replaced local landraces. Wild relatives of these landraces are also disappearing as their habitats are destroyed through human activity. Gene banks preserve both kinds of plants because, as argued by Nikolai Ivanovich Vavilov in 1926, crop plant improvement can best be accomplished by taking advantage of these preserved genetic stocks. Vavilov also noted that genetic variation for most cultivated species was concentrated in specific regions, his “centers of diversity,” most of which are regions where crop species originated.

The vulnerability to parasites and climate of an agriculture that relies on one or a few varieties of crops necessitates the maintenance of adequate reserves of genetic material for breeding. In addition to the preservation of species known to be useful, many people advocate preservation of wild species for aesthetic reasons as well as for their unknown future potential.

The Maintenance of Productivity

Farmers in developed nations change crop varieties every four to ten years in order to maintain consistent levels of food production. This necessitates an ongoing search for new breeds with higher yields and an ability to withstand several environmental challenges, including resistance to multiple pests and drought. Over time, older varieties either mutate, become less popular at the marketplace, or are unable to adapt to new conditions. However, farmers from developing nations are not always able to take advantage of the new breeds or afford the expensive support systems, including chemical fertilizers. Moreover, not all types of crops have benefited equally from conservation efforts.

Another tension between the world’s developing and developed nations concerns ownership of genetic diversity. The Convention on Biological Diversity, signed by 167 nations in 1992, states that genetic material is under the sovereign control of the countries in which it is found. This policy is particularly controversial regarding medicinal plants, because “biodiversity prospecting” for new drugs has economically benefited either individuals or corporations based in the developed countries. By 2023, the convention had been ratified by 196 nations, had obtained 713 pledges of action, and maintained 274 partnership initiatives with various action agendas, including categories ranging from the sustainable use of species to urban development.

Bibliography

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Van der Werf, Julius, et al., editors. Adaptation and Fitness in Animal Populations: Evolutionary and Breeding Perspectives on Genetic Resource Management. Springer, 2009.