But humanity did not everywhere remain in this stage. In Asia they found animals that could be tamed and propagated in captivity. The wild buffalo cow had to be hunted down; the tame cow gave birth to a calf once a year, and also furnished milk. Some of the most advanced tribes--Aryans, Semites, perhaps also Turanians--devoted themselves mainly to taming, and later to raising and tending, domestic animals. The segregation of cattle raising tribes from the rest of the barbarians constitutes the first great division of social labor. These stock raising tribes did not only produce more articles of food than the rest of the barbarians, but also different kinds of products. They were ahead of the others by having at their disposal not alone milk, milk products, and a greater abundance of meat, but also skins, wool, goat's hair, and the spun and woven goods which the growing abundance of the raw material brought into common use. This for the first time made a regular exchange of products possible. In former stages, exchange could only take place occasionally, and an exceptional ability in manufacturing weapons and tools may have led to a transient division of labor. For example, unquestionable remains of workshops for stone implements of the neolithic period have been found in many places. The artists who developed their ability in those shops, most probably worked for the collectivity, as did the artisans of the Indian gentile order. At any rate, no other exchange than that within the tribe could exist in that stage, and even that was an exception. But after the segregation of the stock raising tribes we find all the conditions favorable to an exchange between groups of different tribes, and to a further development of this mode of trading into a fixed institution. Originally, tribe exchanged with tribe through the agency of their tribal heads. But when the herds drifted into the hands of private individuals, then the exchange between individuals prevailed more and more, until it became the established form. The principal article of exchange which the stock raising tribes offered to their neighbors was in the form of domestic animals. Cattle became the favorite commodity by which all other commodities were measured in exchange. In short, cattle assumed the functions of money and served in this capacity as early as that stage. With such necessity and rapidity was the demand for a money commodity developed at the very beginning of the exchange of commodities.