Introduction

It is convenient to divide the evolutionary history of the present day domestic fowl into three phases: the first is the evolution of the genus Gallus, the second is the emergence of the domestic fowl from its progenitor(s) within the genus Gallus, and the third is the appearance of the large number of present day breeds and varieties. These three phases occupy very different time spans. The origin of life on earth is estimated to have occurred about 3000 million years ago, whereas the genus Gallus probably dates from about 8 million years (Helm-Bychowski & Wilson, 1986). The domestication of the fowl in the region of the Indus valley is believed to have occurred by 2000 BC (Zeuner, 1963), but more recent archaeological evidence shows that a much earlier domestication occurred in China c. 6000 bc (West & Zhou, 1989). The origin of most of the present day breeds and varieties dates from the last century, although a few are considerably older. Figure 1.1 illustrates the phases of evolution up to that of the genus Gallus, in relation to other significant events. In this chapter these three phases are considered in turn giving some of the supporting evidence for each stage in evolution.