ABSTRACT The land-use mosaic (i.e. the juxtaposition of cultures giving evidence of social groups) is quite obvious for Epipalaeolithic, especially for its "mesolithic" part. It existed before in all periods. Synchronical cultures are different in the style of débitage and tool manufacturing, often in the pro- portions of the latter, sometimes in specific tools. J. Walzak (1997) shows that the difference between the Middle Ardennian debitage and the Middle Tardenoisian debitage is the result of precise striking, within a similar "chaîne opératoire" of tangential percussion; the Tardenoisians would strike close to the edge, and produced lots of bladelets; the Ardennians were less precise and obtained more flakes and blades. That explains the Fépin style, which is typical of Ardennian, and its differences with the Tardenoisian's Coincy style. Retouched flakes, blades and bladelets are one functional category, their proportions derive only from those obtained by debitage. The only significant difference between both cultures is in the proportions of manufactured, therefore wanted, pointed armatures in each of them. Should that choice correspond to the use by the Ardennians of supply-ways which did not need arrows, or the use of several armatures per arrow by the Tardenoisians, anyway only the choice of the hunting implements determined the technical variants of flint debitage. The same kind of determination can be found at the Beaugencians' with a different style. The Limbourgians' preference for endscrapers, the use of prismatic tools by several cultures surrounding Beaugencian, show that there were other factors about the common tools and emphasize that the Mesolithic cultures had a far greater diversity than Magdalenian groups, in which hunting armatures were more unvarying, and even than Aziloid groups. The time mosaic (the succession of flint and bone technics, which were called "cultures" or "civilisations" improperly) is made of unceasing changes, some of them being more important and coarser than others. All these changes were progressive, correlative (within each regional group) and indépendant (in either group). Minor changes, more perceptible because they were slower, changed the industries without modifying the essential balance, because they did not upset the basic technics. For example the Tjonge- rians who left the Magdalenian style of debitage and provided rough blades, more suitable for the new dart pattern: the end (tools) came before the means (manufacturing technics). The great changes in industries, originating the names (Aurignacian, Gravettian, Solutrean, Magdalenian), were caused by capital choices in a field of first importance, hunting: changing from bone points, made with burins, to flint points (burins disappeared then, the increasing of endscrapers was only apparent), and reciprocally. Here again, the choice of hunting implements determined the composition of the lithic industry, the other social life elements varied sometime else. Whenever it followed some great invention, the "explosive" development of the new ways might appear as an advanced stage of use, therefore some intrusion from outside. The time mosaic in the Upper Palaeolithic had no other origin that those changes happening locally through successive choices or (and) inventions, in the same context as hunting with javelins or spears, which is the true definition of the Upper Palaeolithic. We do not know the reasons of the changes in the early Upper Palaeolithic, when never one of both patterns prevailed thoroughly, later the invention of spear- throwers was essential. The re-invention of the bow put an end to that technical cycle, and gave birth to a more efficient one, which also went through important changes later. The deep-lying causes of all these changes are not the climatic changes. That old postulate was often proved to be wrong, and was never confirmed. Examining carefully the beginnings of each change sometimes shows that they occured before the climatic variation which they were supposed to depend on (should they have induced them ?). It was still the case in a recent study (of a high level in other respects) in which indices and proves are mistaken, without any attempt to find the generality of the facts nor analyse the moment they began. Inventing under the permanent pressure of the environment was the genuine mechanism of that cultural evolution. Though, some discoverers were not followed, because the social corps were unable to understand and adopt new devices, which disappeared: 4000 years for the spearthrowers, 8000 for bows, spans of time far longer than those of the social effects of invention (500 to 1000 years for those periods). The average brains had not yet evolved enough. Then the fundamental cause of the changes was in the biological brain of our species going on evolving.