''Close to 1.4 million living species have been identified. The major ones are 750,000 insects, 41,000 vertebrates, and 250,000 plants. The remainder are invertebrates, mushrooms, algae, and microorganisms (Wilson, 1988). Almost 3,000 plants have been investigated for food or for other uses; however, just 100 have been studied in depth. Throughout time humans have tended to concentrate on obtaining nourishment from a few plants. Today, only 150 plant species are cultivated, twelve of them providing approximately 75 percent of our food. Four of them produce more than half of the food consumed. Most people in the world are fed with cereals such as wheat, rice, millet, and sorghum; tubers such as potatoes, sweet potatoes, and cassava; legumes such as beans, soybeans, and peanuts; and other crops such as sugarcane, sugar beets, cocoa, and bananas (National Research Council, 1975; Harlan, 1992) In 1992 the Genreal Director of the food and agriculture Organization alerted the world to this backward evolution and said that as a result human nutrition was suffering. He also pointed out that the vulnerability of agriculture was increasing and that humans were in danger, as they had only a few sources from which to obtain food (Vietmeyer, 1978; Saouma, 1992). The human food supply now depends on a small number of species, and the failure of one of them could mean starvation for millions of people........People have become very dependent upon cereal grains. Hunter Gatherers ate more than 100 species of plants and animals in the course of a year. Modern humans depend on barely twenty sepcies of plants, four mammals cattle, sheep, pigs, and goats) and one bird (chicken) for the bulk of there nourishment. From the twenty plant species eaten, only four are cereals (wheat, corn, rice and barley), and these form 70 percent of modern western diets. This dependance on a few species puts Western civilisations in a very precarious situation if diseases or pests were to threaten any of these plants. Additionally, intensive medical and nutritional rsearch has demonstrated the importance a diversified diet has in maintaining human health Krauss et al.,2000 ''
''The United States in 1900 was predominantly rural, with nearly 40 percent of the population living on farms . By the 1990s only 1.9 percent of Americans were living in farm households (Beale, 2001).
With human evolution, changes in living were accompanied by changes in food. Modern diets are very different from those of closely related primates and almost certainly from those of early hominidsand preagricultural but anatomically modern humans who lived 30,000 years ago (Wadley and Martin, 1993). Humans have been on earth for 3-5 million years, and for than 99 percent of this time they lived as hunters and gatherers. Only in the last 10,000 years, from the neolithic to the present, did they domesticate plants and animals and transition to an agricultural lifestyle (Engel, 1987; Harlan, 1992). It has been estimated that the typical diet of the paleolithic period (2million-10,000 B.C.) consisted of 50 percent plant based foods and 50 percent from animal origin. Preagricultural foods came from wild game-such as deer, bison, horses, mammoths-fish, wild plants, whole grains, and honey, but no dairy products, oils, and salt were consumed (Cowan and Watson, 1992; Lichtenstein, 1999)
According to Simopoulos (1999a), the spontaneous mutation rate for DNA is estimated at 0.5 percent per million years. Therefore, during the agricultural period there has been little if any chsnge in human DNA. Most human evolution took place during the time of paleolithic diets; hence, genetically, humans remain adapted to a paleolithic diet (Wadley and Martin, 1993; Eaton and Eaton III, 1999, 2000). Data from archaeological findings support the concept that the genetic makeup of human beings as it exists today was developed by a paleolithic diet. Epidemiological studies and controlled experiments strongly support the need to return to that diet (Eaton et all.,1998; Simoplous, 198; Eaton and Eaton III, 2000)''
Fatty acids stimulate and maintain life functions in humans and are considered a macronutrient in human nutrition. In Western diets fatty acids generally constitute the major source of calories. On the other hand, in Asia and undeveloped countries carbohydrates provide the main caloric resource (Nelson. 1992). Fatty acids and there metabolic products serve three basic functions:
1. They act as a highly efficient ernergy reserve that provides protection against external agents like cold weather Mugli and clough, 194; Nettleton, 1995).
2. They are a fundemental constituent of celuar membranes, giving them an elsatic cover that protects each cell (muggli and Clough, 1994; Nettleton, 1995).
3. They act as precursors (i.e, they are the source) from which are made an imoprtant group of hormonal compounds called prostaglandins, thromboxanes, and leukotrienes, which are involved in many physiological processes associated with the central nervous system, hormonal functions, regulation of blood pressure, cholsterol transport, immunoligical mechanisms, and inflammatory reactions (American Heart Association, 1988; Welch and Borlakoglu, 1992; Muggli and clough, 1994; Nettleton, 1995)''