Animal Breeding
Selectivity is one of nature's ways of ensuring the health and survival of plant and animal species. For example, when an unhealthy chick is evicted from its nest or when a healthy pine tree crowds out others that are less vigorous in the competition for light and soil, natural selection is taking place for the good of the species. Human beings, whether knowingly or unknowingly, have been a part of this process for ten thousand years. By selecting the plumpest seeds for planting and the healthiest animals from a litter of puppies, people involve themselves in the natural selection process.
The domestication and breeding of animals began around 9000 b.c. It is even possible that humanity's close relationship with dogs began at the end of the Ice Age. Animal breeding represents a deliberate effort to induce specific traits beneficial to man. Breeding weeds out undesirable characteristics and channels the desirable genes into future generations. The intent may be to keep a genetic strain purebred, as with pedigrees, or it may be to crossbreed, producing trait combinations which, if left to chance, may never have occurred. Crossbreeding is practiced among different species and among groups within species. For instance, a male donkey can be crossbred with a female horse, or mare, to produce a mule. Mules possess the strength of the donkey and the agility and temperament of the horse. Mules, like most hybrids, are sterile, incapable of reproducing. Selection is done to mass-distribute a desired trait among a stock of animals. The greatest example of successful selectivity is in the dairy industry. The high demands placed on dairymen for cleanliness and product quality and consistency have resulted in high standards in testing and record-keeping, both of which are essential for higher gains in selection efforts. This was made possible by the establishment of strong dairy associations in the early 1900s.
One of the earliest methods of human intervention in animal reproduction was artificial insemination. The Arabs practiced it as early as the 1320s. In 1420, French monk Dom Pinchon attempted the artificial fertilization of fish eggs, and in 1780, Italian physiologist Lazzaro Spallanzani (1729-1799) experimented with artificial insemination to obtain puppies. English biologist Robert Bakewell (1725-1795), the founder of the science of animal breeding, developed several new breeds of livestock in the late 1700s. Only within the last two hundred years has science developed an understanding of the hereditary process. The result of this new knowledge has been the direct involvement, especially in the last twenty years, with gene structures, the mechanics of heredity. An accurate understanding of the principles of heredity began with the research of Austrian monk and botanist Gregor Mendel (1822-1884), considered the father of genetics. His experiments with garden peas established the existence of the paired hereditary units he called genes. His findings were relevant to plants, animals and humans alike. Mendel's work coupled with the theories of Charles Darwin (1809-1882) formed the basis of genetics research during the twentieth century; however, Mendel's laws went unnoticed until they were rediscovered in 1901. Research during the 1920s and 1930s by American Jay L. Lush applied Mendel's work directly to animal breeding. Statistical research was conducted by American geneticist Sewall Wright on evolution theory and by the team of C. R. Henderson and Alan Robertson.
The discovery in 1953 of deoxyribonucleic acid ( DNA) by American biologist James D. Watson (1928-) and English biologist Francis Clark has led to the new field of genetic engineering. DNA, the "stuff of life," is the spiral-ladder-shaped structure within every living cell that determines the genetic makeup of every individual. Genetic engineering of the 1980s and 1990s was successful enough in plants to allow for the preliminary marketing of gene-altered tomatoes and potatoes. Desired traits are achieved by the direct injection of genes into plant and animal cell nuclei.
Animal genetics has been marked by a low success rate although the birth in early 1997 of Dolly, a sheep cloned at the Roslin Institute near Edinburgh, Scotland may change that outlook. Dolly was cloned from adult cells, a follow up to an earlier experiment in which a pair of lambs were cloned from fetal fibroblast cells in 1996. Ethical debates concerning this process will undoubtedly continue for a long time to come, particularly as issues of human cloning proliferate.
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