Researchers led by Robert Waterston compared the genomes of Caenorhabditis elegans and Caenorhabditis briggsae and report in PLoS Biology that chromosomal organization may affect an organism's fitness. By looking at these two strains of Caenorhabditis, whose most recent common ancestor lived about 100 million years ago, they discovered that their chromosomes shared a similar architecture – genes pretty much stayed on the same chromosome and only a few intrachromasomal rearrangements occurred.