Species and nations have a lot in common. What, for example, is a german? The tribe has a shared and guttural means of communication that interrupts intercourse of most kinds, but the attribute is equivocal, for austrians speak the same language. Since 1913, the country has defined its own citizens by descent, by German blood (whatever that might be). It includes within the realm the remnants of the Saxon diaspora (many of whom - Romanians included - cannot speak german at all), but cuts out children born in Berklin of Turkish parents. Until the fall of the Berlin wall, indeed, a geographical barrier made many of the nation's citizen more alien to one another than Westerners or Easterners were to the French or the Poles. A century ago German identity itself meant little, as there were only Prussians, Bavarians and Rhinelanders, political entities of their own, each now reduced to variants within a greater Teutonic whole.

The problem of how to define Germans, or any nation, arises because the question is ambiguous: does it turn on shared appearance and behaviour, on geography, or on descent? Is a country an historical entity, or should it be indentified only on criteria that apply today? How much can frontiers be allowed to leak before a nation loses its essence? When will Germans be seen as Europeans, as Prussians have become German?

Such problems of identity turn on natural variation, the raw material of evolutionary change.