@Article{roberts-1998a,
  author         = {Gilbert Roberts and Thomas N. Sherratt},
  title          = {Development of cooperative relationships through increasing investment},
  year           = {1998},
  volume         = {394},
  month          = {July},
  pages          = {175--179},
  read-status    = {short-list},
  journal        = {Nature},
  hardcopy       = {no},
  key            = {roberts-1998a}
}