ies of textual transmission, I imagine that animating the sequence would result in what looks like an exploding firework whose initial burst gives rise to a series of other bursts which in turn gives rise to yet more bursts, and so on, expanding ever outwards. If this is a good analogy, what agents are to blame for driving the fragments apart? The culprits are the copyists.
 Whether by chance or design, copyists introduced novel readings. Once there was a choice of readings, copyists began to choose among those that were already known in their sphere. It seems that typical copyists preferred to choose among existing readings rather than to create novel ones. This is not to say that a copyist would never amend the exemplar's text, especially when faced with an apparent difficulty or corruption. However, there is evidence to suggest that normal practice was to choose among existing readings. For example, the UBS4 apparatus of Hebrews shows that the number of readings in a variation unit follows a certain pattern:
 Here, the number of readings in a variation unit is usually two, perhaps three or four, but seldom more. If copyists were creating new readings all the time then one would expect the frequency of variation units with more than a few readings to be greater.
 Given that the main outcome of the copying process was to reproduce known readings, what determined which ones would be chosen at a particular place and time? If readings had a high mobility then copyists in far flung places would be aware of them and so be able to select them in preference to others. These “viral” readings would then spread throughout the population of texts with ease. If, on the other hand, readings were not so mobile then the preponderance of those available for selection would be local ones. If this was the case then one would expect geographically localised species of text to arise. Regardless of the mobility of readings, the particular reading chosen when the copyist knew there were alternatives was a matter of scribal psychology: whatever reading was best adapted to be selected by the scribe had the best chance of being reproduced.
 The question of whether local texts were likely to form during a particular phase of textual history then comes down to the question of how mobile readings were at the time. This, in turn, rests on the question of how mobile the vectors of the viral readings were, namely the manuscripts. Epp shows that during the first few centuries of the Christian era, letters and documents could be transported far and wide with surprising speed. Nevertheless, I suggest that the principle of least effort, which is useful for understanding many human enterprises, would make it preferable to pick up a nearby exemplar rather than send for an exotic one when a copy had to be made.
 What then? Were manuscripts so mobile as to make the development of local texts unlikely? It seems that MDS maps provide a clue and at the same time give us reason to revisit a theory of the text which has fallen out of favour. The following figure shows a two-dimensional projection of the classical MDS result obtained from the Hebrews data:
 Strangely enough, there seems to be a correspondence between this map and a physical map of the Mediterranean:
 A number of broad correlations between textual clusters and early Christian population centres emerge when the MDS and physical maps are compared:
Members of the “Western” cluster (e.g. Old Latins and Vulgate) are to the west.
A great cloud of witnesses spreads across an arc encompassing the north-eastern and eastern shores of the Mediterranean. This cloud includes a number of witnesses whose textual locations correspond to their suspected geographical provenances, such as Chrysostom, the Byzantine standard text, and the Syriac versions.
The “secondary Alexandrian” cluster (A, C, 33, etc.) corresponds to Egypt.
 If the correlation between textual clusters in MDS maps and physical locations of Christian population centres around the Mediterranean rim is more than coincidental then MDS maps can be used 