The religion and belief system of the Indus valley people have received considerable attention, especially from the view of identifying precursors to deities and religious practices of Indian religions that later developed in the area. However, due to the sparsity of evidence, which is open to varying interpretations, and the fact that the Indus script remains undeciphered, the conclusions are partly speculative and largely based on a retrospective view from a much later Hindu perspective. An early and influential work in the area that set the trend for Hindu interpretations of archaeological evidence from the Harrapan sites was that of John Marshall, who in 1931 identified the following as prominent features of the Indus religion: a Great Male God and a Mother Goddess; deification or veneration of animals and plants; symbolic representation of the phallus (linga) and vulva (yoni); and, use of baths and water in religious practice. Marshall's interpretations have been much debated, and sometimes disputed over the following decades.