Some scholars trace the origins of natural science as far back as pre-literate human societies, where understanding the natural world was necessary for survival.[5] People observed and built up knowledge about the behavior of animals and the usefulness of plants as food and medicine, which was passed down from generation to generation.[5] These primitive understandings gave way to more formalized inquiry around 3500 to 3000 BC in the Mesopotamian and Ancient Egyptian cultures, which produced the first known written evidence of natural philosophy, the precursor of natural science.[6] While the writings show an interest in astronomy, mathematics and other aspects of the physical world, the ultimate aim of inquiry about nature's workings was in all cases religious or mythological, not scientific.[7]

A tradition of scientific inquiry also emerged in Ancient China, where Taoist alchemists and philosophers experimented with elixirs to extend life and cure ailments.[8] They focused on the yin and yang, or contrasting elements in nature; the yin was associated with femininity and coldness, while yang was associated with masculinity and warmth.[9] The five phases – fire, earth, metal, wood and water – described a cycle of transformations in nature. Water turned into wood, which turned into fire when it burned. The ashes left by fire were earth.[10] Using these principles, Chinese philosophers and doctors explored human anatomy, characterizing organs as predominantly yin or yang and understood the relationship between the pulse, the heart and the flow of blood in the body centuries before it became accepted in the West.[11]

Little evidence survives of how Ancient Indian cultures around the Indus River understood nature, but some of their perspectives may be reflected in the Vedas, a set of sacred Hindu texts.[11] They reveal a conception of the universe as ever-expanding and constantly being recycled and reformed.[11] Surgeons in the Ayurvedic tradition saw health and illness as a combination of three humors: wind, bile and phlegm.[11] A healthy life was the result of a balance among these humors.[11] In Ayurvedic thought, the body consisted of five elements: earth, water, fire, wind and empty space.[11] Ayurvedic surgeons performed complex surgeries and developed a detailed understanding of human anatomy.[11]

Pre-Socratic philosophers in Ancient Greek culture brought natural philosophy a step closer to direct inquiry about cause and effect in nature between 600 and 400 BC, although an element of magic and mythology remained.[12] Natural phenomena such as earthquakes and eclipses were explained increasingly in the context of nature itself instead of being attributed to angry gods.[12] Thales of Miletus, an early philosopher who lived from 625 to 546 BC, explained earthquakes by theorizing that the world floated on water and that water was the fundamental element in nature.[13] In the 5th century BC, Leucippus was an early exponent of atomism, the idea that the world is made up of fundamental indivisible particles.[14] Pythagoras applied Greek innovations in mathematics to astronomy, and suggested that the earth was spherical.[