title: The evolutionary position of nematodes.
abstract: BACKGROUND
  The complete genomes of three animals have been sequenced by global research efforts: a nematode worm (Caenorhabditis elegans), an insect (Drosophila melanogaster), and a vertebrate (Homo sapiens). Remarkably, their relationships have yet to be clarified. The confusion concerns the enigmatic position of nematodes. Traditionally, nematodes have occupied a basal position, in part because they lack a true body cavity. However, the leading hypothesis now joins nematodes with arthropods in a molting clade, Ecdysozoa, based on data from several genes.
  
  
  RESULTS
  We tested the Ecdysozoa hypothesis with analyses of more than 100 nuclear protein alignments, under conditions that would expose biases, and found that it was not supported. Instead, we found significant support for the traditional hypothesis, Coelomata. Our result is robust to different rates of sequence change among genes and lineages, different numbers of taxa, and different species of nematodes.
  
  
  CONCLUSIONS
  We conclude that insects (arthropods) are genetically and evolutionarily closer to humans than to nematode worms.
authors: Astrobiology Research Center and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA. jeb322@psu.edu
authors: Jaime E
authors: JE
authors: Blair
authors: Kazuho
authors: K
authors: Ikeo
authors: Takashi
authors: T
authors: Gojobori
authors: S Blair
authors: SB
authors: Hedges
mesh_terms: D000818:Animals; D015982:Bias; D017173:Caenorhabditis elegans / Q000145:classification* / Q000235:genetics*; D004331:Drosophila melanogaster / Q000145:classification / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D010802:Phylogeny
chemical_list: D009687:Nuclear Proteins