Fifteen hundred years is ample time in which to lose mutual comprehension. Iceland was colonized by the Norwegians at the end of the ninth century AD. Today's Icelanders, with considerable effort, can understand people from the Scandinavian peninsula, but the Scandinavians hardly understand the Icelanders. A thousand years is the minimum time span for a language to change so much that it becomes incomprehensible.

We chose to do this work mathematically, which has the advantage of precision but is not always appreciated by readers. It is perhaps for this reason that anthropologists have not shown much interest in these models, unlike economists, for example, for whom the use of mathematics poses no problem. However, one could reach the same conclusions by using just a bit of common sense.

Fifteen hundred years is ample time in which to lose mutual comprehension. Iceland was colonized by the Norwegians at the end of the ninth century AD. Today's Icelanders, with considerable effort, can understand people from the Scandinavian peninsula, but the Scandinavians hardly understand the Icelanders. A thousand years is the minimum time span for a language to change so much that it becomes incomprehensible.

Specific units - such as memes are intended to represent have meaning when there is essential discontinuity between categories. Such convenient discontinuities are found in atoms, elementary particles, genes, and DNA.

Mathematics may be the only exception in the sciences that leaves no room for skepicism. But, if mathematical results are exact as no empirical law can ever be, philosophers have discovered that they are not absolutely novel - instead, they are tautological.