"It is clear that the human species is currently an eater of grass seeds. We have become 'canaries.'It is also clear that the world's food supply depends on 12 or 15plant species. It probably was not always so, although wheat, barley, rice, and maize have been the foundations of our high civilizations. The current trend is for the major crops to become even more major and for the lesser ones to dwindle."1
n fact, although there are approximately 200,000
I species of flowering plants, only six species—wheat, rice, corn, potato, sweet potato, and cassava—provide 80% of the calories consumed by humans worldwide (Fig. 14.1). An additional eight plants—sugar cane, sugar beet, bean, soybean, barley, sorghum, coconut, and banana—complete the list of major crops grown for human consumption.
In the 2 million years that we have inhabited this earth, we have cultivated plants for only the most recent 10,000 years, or less than 1% of our history. However, in that time, we have dramatically changed the plant landscape and our own lives. Hunter-gatherer societies have given way to agricultural societies and the development of cities and civilizations. Such concentrations of people are vulnerable to catastrophes such as drought and famine. Domesticated plants depend on us for their survival, but we have also become dependent on them for our survival.
We domesticate plants by altering them genetically to meet our needs. Strictly speaking, a domesticated plant is one whose reproductive success depends on human intervention. This is an ongoing evolutionary process, and plants are found in a continuum from purely wild to fully domesticated. Our current crop plants continue to evolve as a result of our
breeding efforts. However, we are becoming increasingly dependent on fewer and fewer species of plants. It is amazing that, although humans have eaten thousands of types of plants in the past, we currently rely on only a handful to supply almost all of our nutritional needs.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.