In unpublished work, P. E. Cowan finds Rattus rattus, like R. norvegicus, to be markedly neophobic. These commensal species have been compared with two Australian congeners, R. fuscipes and R. villosissimus, both largely independent of man and neither neophobic in the laboratory conditions in which they have been tested. The typical new object reaction, first clearly described in investigations of rats as pests, is perhaps a product of natural selection in man-made environments. But there is no universal rule: the commensal house mouse, Mus musculus, displays, instead of typical neophobia, a capricious and unpredictable kind of behavior […]