Before revision:  As biological cells are inherently mass-conserved systems, our results provide a key concept to understand the ubiquitous occurrence of actin waves in cells, explaining why they are so common, and why their dynamics is robust and long-lived.
After revision:  As biological cells are inherently mass-conserved systems, our results provide a key concept to understand the ubiquitous occurrence of actin waves in cells, suggesting why they are so common, and why their dynamics is robust and long-lived.