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 practised hunting or slash-and-burn agriculture came into closer contacts with another group in the valleys which practised 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.

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

The Yang-shao culture takes its name from a prehistoric settlement in the west of the present province of Honan, where Swedish investigators discovered it.  Typical of this culture is its wonderfully fine pottery, apparently used as gifts to the dead.  It is painted in three colours, white, red, and black.  The patterns are all stylized, designs copied from nature being rare.  We are now able to divide this painted pottery into several sub-types of specific distribution, and we know that this style existed from c. 2200 B.C. on.  In general, it tends to disappear as does painted pottery in other parts of the world with the beginning of urban civilization and the invention of writing.  The typical Yang-shao culture seems to have come to an end around 1600 or 1500 B.C.  It continued in some more remote areas, especially of Kansu, perhaps to about 700 B.C.  Remnants of this painted pottery have been found over a wide area from Southern Manchuria, Hopei, Shansi, Honan, Shensi to Kansu; some pieces have also been discovered in Sinkiang.  Thus far, it seems that it occurred mainly in the mountainous parts of North and North-West China.  The people of this culture lived in villages near to the rivers and creeks.  They had various forms of houses, including underground