The origin of rice is not yet known; according to some scholars, rice was first cultivated in the area of present Burma and was perhaps at first a perennial plant.  Apart from the typical rice which needs much water, there were also some strains of dry rice which, however, did not gain much importance.  The centre of this Tai culture may have been in the present provinces of Kuangtung and Kuanghsi.  Today, their descendants form the principal components of the Tai in Thailand, the Shan in Burma and the Lao in Laos.  Their immigration into the areas of the Shan States of Burma and into Thailand took place only in quite recent historical periods, probably not much earlier than A.D. 1000.

Finally there arose from the mixture of the Yao with the Tai culture, at a rather later time, the Yueeh culture, another early Austronesian culture, which then spread over wide regions of Indonesia, and of which the axe of rectangular section, mentioned above, became typical.

Thus, to sum up, we may say that, quite roughly, in the middle of the third millennium we meet in the north and west of present-day China with a number of herdsmen cultures.  In the south there were a number of agrarian cultures, of which the Tai was the most powerful, becoming of most importance to the later China.  We must assume that these cultures were as yet undifferentiated in their social composition, that is to say that as yet there was no distinct social stratification, but at most beginnings of class-formation, especially among the nomad herdsmen.

[Illustration:  Map 1.  Regions of the principal local cultures in prehistoric times. Local cultures of minor importance have not been shown.]

6 The Yang-shao culture

The various cultures here described gradually penetrated one another, especially at points where they met.  Such a process does not yield a simple total of the cultural elements involved; any new combination produces entirely different conditions with corresponding new results which, in turn, represent the characteristics of the culture that supervenes.  We can no longer follow this process of penetration in detail; it need not by any means have been always warlike.  Conquest of one group by another was only one way of mutual cultural penetration.  In other cases, a group which occupied the higher altitudes and practiced hunting or slash-and-burn agriculture came into closer contacts with another group in the valleys which practiced some form of higher agriculture; frequently, such contacts resulted in particular forms of division of labour in a unified and often stratified new form of society.  Recent and present developments in South-East Asia present a number of examples for such changes.  Increase of population is certainly one of the most important elements which lead to these developments.  The result, as a rule, was a stratified society being made up of at least one privileged and one ruled stratum.  Thus there came into existence around 2000 B.C. some new cultures, which are well known archaeologically.  The most important of these are the Yang-shao culture in the west and the Lung-shan culture in the east.  Our knowledge of both these cultures is of quite recent date and there are many enigmas still to be cleared up.