NRC Admits Mutation Not Sufficient Explanation for Evolution

I thought this was worth sharing:

On Page 8 of a Report from the National Research Council there is an interesting admission:

“Natural selection based solely on mutation is probably not an adequate mechanism for evolving complexity.”

Of course the report itself supports the concept of Darwinian evolution. But I think the admission that mutation is an insufficient mechanism is significant.
They invoke lateral transfer of genes as the alternate explanation:

“More important, lateral gene transfer and endosymbiosis are probably the most obvious mechanisms for creating complex genomes…”

Of course this begs the question; where did the genes come from that are being laterally transferred?
As far as I saw in the report, the authors only indirectly address this problem by speculating that viruses or “virus-like entities” with rapid mutation and replication rates were involved in early cellular organism evolution.

I thought this admission by a mainstream publication was significant. And a small step in the right direction.