Parallel adaptive origins of digestive RNases in Asian and African leaf monkeys

Nat Genet. 2006 Jul;38(7):819-23. doi: 10.1038/ng1812. Epub 2006 Jun 11.


Similar morphological or physiological changes occurring in multiple evolutionary lineages are not uncommon. Such parallel changes are believed to be adaptive, because a complex character is unlikely to originate more than once by chance. However, the occurrence of adaptive parallel amino acid substitutions is debated. Here I propose four requirements for establishing adaptive parallel evolution at the protein sequence level and use these criteria to demonstrate such a case. I report that the gene encoding pancreatic ribonuclease was duplicated independently in Asian and African leaf-eating monkeys. Statistical analyses of DNA sequences, functional assays of reconstructed ancestral proteins and site-directed mutagenesis show that the new genes acquired enhanced digestive efficiencies through parallel amino acid replacements driven by darwinian selection. They also lost a non-digestive function independently, under a relaxed selective constraint. These results demonstrate that despite the overall stochasticity, even molecular evolution has a certain degree of repeatability and predictability under the pressures of natural selection.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptation, Physiological
  • Amino Acid Sequence
  • Amino Acid Substitution
  • Animals
  • Colobinae / genetics*
  • Colobinae / metabolism
  • Colobus / genetics
  • Colobus / metabolism
  • Evolution, Molecular
  • Gene Duplication
  • Humans
  • Molecular Sequence Data
  • Pancreas / enzymology
  • Phylogeny
  • Ribonucleases / genetics
  • Sequence Homology, Amino Acid
  • Species Specificity


  • Ribonucleases

Associated data

  • GENBANK/DQ516063
  • GENBANK/DQ516064
  • GENBANK/DQ516065