This chapter discusses one of the fundamental facts in robin life, as in that of many other birds is territory. It determines whether natural selection is really the driving force behind evolution, as Charles Darwin thought. In autumn every male robin occupies a territory of about an acre, in which he spends most of his time, though he occasionally feeds outside it. A robin redbreast in a cage may, as Blake said, put all heaven in a rage; but, if like Mr. Lack's cage, it is thirty feet long, twelve wide, and six high, the robin is quite willing to breed in it, and is much safer than outside. Lack studied the robins in about 20 acres of Devonshire. Lack concludes that where cats and boys are common, about half the nests are destroyed, though most of the nests at Dartington were successful.