In 1984, Graham Twigg published The Black Death: A Biological Reappraisal, where he argued that the climate and ecology of Europe and particularly England made it nearly impossible for rats and fleas to have transmitted bubonic plague. Combining information on the biology of Rattus rattus, Rattus norvegicus, and the common fleas Xenopsylla cheopis and Pulex irritans with modern studies of plague epidemiology, particularly in India, where the R. rattus is a native species and conditions are nearly ideal for plague to be spread, Twigg concludes that it would have been nearly impossible for Yersinia pestis to have been the causative agent of the plague, let alone its explosive spread across Europe. Twigg also shows that the common theory of entirely pneumonic spread does not hold up. He proposes, based on a reexamination of the evidence and symptoms, that the Black Death may actually have been an epidemic of pulmonary anthrax caused by Bacillus anthracis.