I.

Introduction

Breeding, selective control of mating in plants and animals to produce organisms that better serve human needs for food, work, sport, or aesthetics. Simple breeding methods have been employed throughout human history. From paintings on the walls of Egyptian tombs, archaeologists have determined that dogs were bred at least 4000 years ago, and perhaps as early as 10,000 years ago. Ancient civilizations also domesticated varieties of cattle, sheep, goats, and grains.

The history of breeding can be divided into two periods: before and after the rediscovery in 1900 of Mendel's concepts of heredity (see Mendel's Laws). Before 1900, breeders worked primarily by selecting from each generation the animals or plants that displayed desired characteristics and then breeding these individuals to produce the next generation. Although this simple method, known as mass selection, produced some favorable results, it was often a slow and unpredictable process. After the rediscovery of Mendel's work, breeding became more predictable and scientific. Mendel's principles showed that many traits are transmitted as discrete units, and over successive generations these traits do not blend with or become corrupted by other traits. Most importantly, Mendel's work showed that by analyzing breeding results it is possible to predict which traits will occur, and in what proportions, in the next generation. Thus, analysis of breeding results gives the breeder knowledge about genotype (genetic makeup) of an organism based on observation of its phenotype (visual characteristics), and it provides a knowledge of genetic variation for specific traits. Genetic variation is the source for modification from which the breeder draws when selecting for a particular trait. Through these methods modern Mendelian breeding has produced remarkable improvements in a large variety of agriculturally useful organisms.

Animal and plant breeding has been responsible for vastly improving agricultural yields over the past several hundred years, and thus for improving the world's food supply (see Food Supply, World). Systematic breeding programs emerged in Europe and the United States on an increasingly large scale during the Industrial Revolution in the late 18th century, partly in response to the demand for more food to feed an increasingly urban, nonagricultural workforce. In the 20th century, growing world populations have also brought increased pressure to improve agricultural yields.