A simple mechanism could underlie the growth and self-replication of protocells -- putative ancestors of modern living cells -- suggests a study publishing September 3 in Biophysical Journal. Protocells are vesicles bounded by a membrane bilayer and are potentially similar to the first unicellular common ancestor (FUCA). On the basis of relatively simple mathematical principles, the proposed model suggests that the main force driving protocell growth and reproduction is the temperature difference that occurs between the inside and outside of the cylindrical protocell as a result of inner chemical activity.