Emergence biases in molecular evolution

Biases in molecular evolution can significantly influence evolutionary trajectories. They have been described in a variety of contexts such as development and mutation, but not for the emergence of new and observable molecular activities. Here, we formalize the term, emergence bias, as the molecular predisposition that, upon mutation, biases a genetic sequence towards or against manifesting new or latent functions or phenotypes. These biases have been observed in previous studies for the emergence of promoters, enhancers, and de novo proteins, but never formally characterized as such. In this Perspective piece, we describe these studies and synthesize their findings through the prism of a unifying term, emergence bias, to provide support for this new concept, and speculate on its molecular underpinnings. We believe that emergence biases may play an important role in evolution by canalizing which functions can and cannot emerge.