John Conery's research, published in Science, suggests population effects in genome complexity.

The November 21 issue of the leading journal Science includes the following article, jointly authored by Professor John Conery.
THE ORIGINS OF GENOME COMPLEXIMITY
Michael Lynch, Indiana University and John S. Conery, University of Oregon

Abstract:

Complete genomic sequences from diverse phylogenetic lineages reveal notable increases in genome complexity from prokaryotes to multicellular eukaryotes. The changes include gradual increases in gene number, resulting from the retention of duplicate genes, and more abrupt increases in the abundance of spliceosomal introns and mobile genetic elements. We argue that many of these modifications emerged passively in response to the long-term population-size reductions that accompanied increases in organism size. According to this model, much of the restructuring of eukaryotic genomes was initiated by nonadaptive processes, and this in turn provided novel substrate for the secondary evolution of phenotypic complexity by natural selection. The enormous long-term effective population sizes of prokaryotes may impose a substantial barrier to the evolution of complex genomes and morphologies.