Figure 1.

Selective pressure drives the evolution of the biological clock. The biological clocks of various organisms are derived from the selection pressure given by the natural environment. Various selection pressures are the main driving force that drives the biological clock to become more complex and refined. Since the Great Oxygenation Event (GOE) began 3 billion years ago, the biological clock has become more and more complex and manifests in different forms on different species. From the post-translational oscillation (PTO) mechanism to the transcription–translation negative feedback (TTFL) mechanism, the overall biological clock system of life reflects the trend of step evolution.