One way around the problem in (1) is to find a mate that also had an identical chromosomal fusion event. But Valentine and Erwin imply that such events would be highly unlikely:
"[T]he chance of two identical rare mutant individuals arising in sufficient propinquity to produce offspring seems too small to consider as a significant evolutionary event."
(Erwin, D..H., and Valentine, J.W. "'Hopeful monsters,' transposons, and the Metazoan radiation", Proc. Natl. Acad. Sci USA, 81:5482-5483, Sept 1984)
From the article:
Viable mutations with major morphological or physiological effects are exceedingly rare and usually infertile; the chance of two identical rare mutant individuals arising in sufficient propinquity to produce offspring seems too small to consider as a significant evolutionary event.
Hysterical! Luskin is talking about chromosomal fusion and claims Erwin and Valentine say it's unlikely, but Erwin and Valentine are talking about mutations of structural and regulatory genes - not necessarily the same thing! Even more interesting is the gist of the article itself. Erwin and Valentine's article is actually concerned with the origin of morphological novelties - specifically whether "...microevolutionary substitutions involving structural genes..." can be considered a plausible mechanism for morhphological novelties. They say no. Then they suggest an alternative based on horizontal trnasmission of genes via viruses:
Mutations associated with viruses that preferentially insert at specific loci are hardly random; furthermore, a population infected by such a virus would possess numbers of individuals with frequently identical mutations.
A little later in the same article:
Viral transmission of genetic material may also involve the horizontal transmission of new genes or gene variants, enabling them to spread through a population in much less time than fixation requires.
Both of which totally undermine the point of Luskin's quote. Even more interesting is their application of the idea of horizontal and vertical transmission of genes to the Cambrian radiation - but I'll leave that to the reader.
