Almost everything known about Zou Yan comes from a short biography Sima Qian included in the Shi ji, written roughly a century after Zou Yan's own lifetime around 305 to 240 BCE. It describes a scholar of the Jixia Academy in the state of Qi who examined the waxing and waning of yin and yang so thoroughly that he produced essays running past one hundred thousand words, none of which survive. Sima Qian credits him not with a single argument in the manner of Mencius or Han Feizi but with a comprehensive system: combining yin and yang, the paired principles of shade and light, rest and activity, with wuxing, the five phases of wood, fire, earth, metal and water, into a unified account of natural change and, from it, a theory of how ruling dynasties rise and are in turn displaced in a fixed cyclical order.
That last claim mattered politically as much as philosophically. A dynasty that could show its own phase properly followed the one before it, in the sequence the theory predicted, gained a kind of cosmological legitimacy rhetoric alone could not supply, and rulers across the Qin and Han courts competed over which phase their own house represented.
The Han dynasty's bibliographic treatise classed the Yin-Yang school as one of six schools of thought, set alongside the Confucians and the Daoists rather than beneath either, a measure of how seriously Zou Yan's system was taken in its own era even though it left behind no order of disciples and no surviving school text of its own. Zou Yan is also placed at the Jixia Academy, the same milieu credited with the rise of Huang-Lao Daoism, which is part of why the school's categories came to shape Chinese cosmology, medicine and calendrical practice long after Zou Yan's own name had faded from active argument.