AbstractA new model for population growth as a branching process is described. It requires knowledge of the population's age‐specific survivorship and fecundity curves. The total population size at any time is calculated by summing across all branches of the tree representing the population's lineage and thus the model also allows the lineage of the developing population to be traced. Use of the model is demonstrated by a hypothetical example. The model could be of particular value in tracing the phylogenetic development of populations and/or specie