Unconstrained mutation predicts everything and is useless

In his 2001 book Science and Selection, David Hull proposed that prefixing variation with "blind" or "random" was unnecessary:

In sum, statements about the sorts of variation that function in selection processes need not include any reference to their being "blind," "random," or what have you. All of the terms that have been used to modify "variation" are extremely misleading. Hence, we see no reason to put any adjective before "variation" in our definition of selection.

While "blind" and "random" are unfortunate word choices, one can't allow completely unconstrained mutations in evolutionary models - or else they lose all predictive value. If mutation is a completely unconstrained process literally: anything goes.

As far as I can see, Donald Campbell got this issue right long ago - but used the unfortunate term "blind" to describe it. Campbell basically said that variation was generated on the basis of existing knowledge. Since then he has been much misunderstood on this topic, due to a poor choice of terminology.

Alas, while technically correct, the idea of generating variation on the basis of existing knowledge doesn't help modellers very much. Most modellers of evolutionary dynamics typically stick with undirected mutations, which often work pretty well, and are simple to model.