Evolution in Agriculture: The Domestication of Wheat
When humans understand a phenomenon that occurs in nature, they often gain increased control over it or can adapt it to new uses. The domestication of wheat is a good example.
By recovering seeds from different archaeological sites and noticing changes in their characteristics over the centuries, scientists have hypothesized how wheat was altered by humans over time. About 11,000 years ago, people in the Middle East began growing plants for food rather than relying entirely on the wild plants and animals they could gather or hunt. These early farmers began saving seeds from plants with particularly favorable traits and planting those seeds in the next growing season. Through this process of “artificial selection,” they created a variety of crops with characteristics particularly suited for agriculture. For example, farmers over many generations modified the traits of wild wheat so that seeds remained on the plant when ripe and could easily be separated from their hulls. Over the next few millennia, people around the world used similar processes of evolutionary change to transform many other wild plants and animals into the crops and domesticated animals we rely on today.
In recent years, plant scientists have begun making hybrids of wheat with some of their wild relatives from the Middle East and elsewhere. Using these hybrids, they have bred wheat varieties that are increasingly resistant to droughts, heat, and pests. Most recently, molecular biologists have been identifying the genes in the DNA of plants that are responsible for their advantageous traits so that these genes can be incorporated into other crops. These advances rely on an understanding of evolution to analyze the relationships among plants and to search for the traits that can be used to improve crops.
Evolutionary biologists have discovered structures, biochemical processes and pathways, and behaviors that appear to have been highly conserved within and across species. Some species have undergone little overt change in their body structure over many millions of years. At the level of DNA, some genes that control the production of biochemicals or chemical reactions that are essential for cellular functioning show little variation across species that are only distantly related. (See, for example, the DNA sequences for two different genes that are conserved in closely related as well as more distantly related species that are described on pages 30 and 31.)
However, natural selection also can have radically different evolutionary effects over different timescales. Over periods of just a few generations (or,