So with man. If his natural powers of increase were exercised without check, it is only a question of time when the globe itself would be too small for the numbers of human beings, even though equipped with the most effective means of cultivation. In point of fact, population has almost always pressed on the available means of subsistence. The only important exceptions are found in new countries, when opened up to colonists who have brought with them the superior methods of exploitation developed in more advanced civilisations. Thus the history of the human race is largely the record of a struggle for the means of subsistence caused by the pressure of population. Not that the population is necessarily dense. Some of the most thinly scattered peoples have had the greatest difficulty in making a living, simply because the available means of subsistence were exceptionally scanty, as the North American Indians, and above all in the continent of Australia before its settlement by Europeans. The study of human history shows that if the population was small, it was not owing to any defect in the natural powers of increase of human beings. It will be seen that the Malthusian theory rests on two great facts: (1) on the physiological fact, viz. that all human beings are capable of indefinite increase; and (2) on a natural economic fact, that the means of subsistence are not capable of a corresponding indefinite increase, the ultimate reason of this being nothing else than the limited size of the planet on which we live. The inevitable result is the struggle for existence. The Darwinian theory of the struggle for existence has the widest application to human society and human history. This struggle has gone on through a great variety of stages. In the earliest phases of human history it generally resulted in the extermination of the vanquished, and was often associated with cannibalism. As society advanced from the hunting and pastoral into the agricultural state, the victors saw that it would be their interest to spare the vanquished that they might enjoy the benefit of their labour as slaves. In this way began the institution of slavery, on which ancient civilisation rested. The warlike tribes that overturned the Roman Empire found that they could more easily and conveniently utilise the labour of the vanquished under the various forms of serfdom. In modern times free workers, destitute of capital, are ready under a system of competition to perform the labour of society for a wage that renders them the customary subsistence.