Evolution, 4th Edition

What was the most important advance in human history? Fire? The wheel? The

computer? A strong case can be made for the harnessing of evolution by our

ancestors some 11,000 years ago. They bred wheat that provided more grain

and cows that produced more milk. Selective breeding produced domes-

ticated plants and animals that gave the first farmers vastly more food than

their ancestors could have imagined (FIGURE 6.1). For the first time in history,

humans had abundant resources. They abandoned a nomadic lifestyle and

settled in communities that became the earliest villages, towns, and then cit-

ies. Much of civilization—buildings, writing, commerce—only then became

possible. In short, the genetic modification of plants and animals by selective

breeding is the foundation of human civilization. The discovery of the power

of selective breeding is simply the discovery that selection and inheritance

together can produce large evolutionary changes. And, as Darwin pointed

out, evolutionary changes caused by artificial selection of domesticated ani-

mals and plants illustrate what natural selection can do in the wild.

Traits such as crop yield in corn, milk production in cows, and body height in

humans are examples of quantitative traits. These are traits that vary continuously

and that are affected by several, sometimes thousands, of loci (and for that rea-

son they are also called polygenic traits). Quantitative genetics is the study of how

quantitative traits are inherited and how they evolve.

This chapter begins by looking at how genes and the environment affect

quantitative traits, how selection acts on them, and how fast they evolve in

response. The next topic is artificial selection, in which people selectively breed

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The common sunflower (Helianthus annuus) has been selectively bred for its showy

flowers, and to increase its production of oil and seeds. Hundreds of domesticated

animal and plant species have been vastly modified by artificial selection.

Phenotypic Evolution

Evolution

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