specifics of the Genesis story, Maimonides suggested that Adam initially had offspring who were "animal[s] in human shape and form", and only afterwards had offspring who were fully human in terms of intelligence and judgment. Similarly, Nahmanides suggested that God initially created man as a walking humanoid creature, and only afterwards instilled with this creature a human level of intelligence and understanding. Rashi, while his commentary on the verses describing the days of creation teaches them as literal days, brackets his discussion of Genesis ch. 1 with comments stating that the entire world was created at once, with no duration of existence before Adam being specified. Kabbalistic discussion of eras before Genesis Many classic Kabbalistic sources mention Shmitot—cosmic cycles of creation, similar to the Indian concept of yugas. According to the tradition of Shmitot, Genesis talks openly only about the current epoch, while the information about the previous cosmic cycles is hidden in the esoteric reading of the text. Isaac ben Samuel of Acre (13th century), a prominent kabbalist and disciple of Nahmanides, calculated based on this theory that the Universe is about 15 billion years old. Since (he reasoned) shmitot existed before man was created, time before Adam and Eve must be measured in divine years, not human years. Psalm 90:4 says, "For a thousand years in thy sight are but like yesterday when it is past", thus one divine day equals 365,250 (assuming a 365.25-day year) human days. Like Livnat Ha-Sapir, he held that we are in the seventh shmita, each of which lasts 6000 years. Overall, then, Isaac calculated the age of the universe at Adam's creation to be 7 * 6000 * 365,250 = 15,340,500,000 years. In his commentary on the Torah, Rabbi Bahya ben Asher (11th century, Spain) concludes that there were many time systems occurring in the universe long before the spans of history that man is familiar with. Based on the Kabbalah he calculates that the Earth is billions of years old. Jewish views in reaction to Darwin With the advent of Charles Darwin's evolutionary theory, the Jewish community found itself engaged in a discussion of Jewish principles of faith and modern scientific findings. Post-1800 Kabbalistic views of compatibility Rabbi Elijah Benamozegh, an Italian Kabbalist, changed his position over time with respect to evolutionary theory. His views went through three stages, corresponding to his engagement with ideas of transmutation in three key works,