Anomalies and the Eve effect in the asexual Penna model

The Penna model of evolutionary ageing is an influential model of mutation accumulation and selection, where an individual's genomic information is represented by a binary bit string. One key parameter of the model is the death threshold, T, the number of diseases any particular individual is able to endure. We show, by combined computer simulations and analytical formulation, that certain anomalies emerge in the asexual Penna model for T>1, which may lead to the so-called Eve effect. We characterize these anomalies and their associated demographic distributions. We argue that this anomaly is similar in nature to the well known first-passage problem.