Agronomy

Most varieties of agricultural crops look and grow very differently than their wild progenitors. In fact, almost all of the domesticated species of plants and animals that humans depend upon as sources of food, materials, or energy have been selectively bred for various desirable traits. This evolutionary process has resulted in the development of substantial genetic differences between domesticated varieties and their wild ancestors—differences that have arisen because of deliberate selection of desirable traits by humans.

Selective breeding of agricultural species has been very important in improving their productivity under cultivation. Enormous increases in the useful yields of cultivated plants have been attained through geneticallybased improvements of growth rates. These include responses to the addition of fertilizer, along with modifications of the growth form, anatomy, and chemistry of crops. Similarly, domesticated animals have been selectively bred for growth rates, compliant behavior, chemical quality of their produce, and other desirable traits.

Selective breeding of some agricultural species has been so intensive and thorough that they can no longer survive without the assistance of humans, that is, in the absence of cultivation. For example, the seeds of maize (corn) can no longer disperse from their cob because of the tightly enclosing leaves that have evolved as a result of selective breeding. Similarly, our dairy cows are no longer capable of surviving on their own—they require humans to milk them, or they die from the complications of mastitis.

Selective breeding of existing and potential agricultural species still has a great deal to contribute to future developments in agronomy. Existing crops require continual genetic refinements to make them more suitable to the changing environmental conditions of agricultural ecosystems, to improve their resistance to diseases and pests, and to improve their nutritional qualities. At the same time, continuing surveys of the diversity of wild species will discover many plants and animals that are of potential benefit to humans. Selective breeding will be a critical part of the process by which those new biodiversity resources are domesticated.