Computer Simulation of Sympatric Speciation with Penna Ageing Model

The common ancestors of today’s humans and today’s chimpanzees presumably lived several million years ago. Then, due to genetic mutations and/or changes in the environment, the population split into the ancestors of humans and the ancestors of chimpanzees. Such a separation of one species into two is called “speciation”. It is easily explained if the two populations live in separate environments, like one on an island and the other on a continent, making the mating of males from one population with females from the other population impossible. This effect is called allopatric speciation. More difficult to explain is sympatric speciation, where the two populations continue to live in the same environment but nevertheless cease to mate each other [1]. A recent computer model [2] in the physics literature also cites biological examples, serving as a background also for our paper. We concentrate here on models with age-structured populations [3, 4, 5] and in particular use the Penna bitstring model [6, 7], which is the presently most widespread model to simulate biological ageing. We deal only with sexual reproduction where two populations are defined as being different species if the mating from different populations produces no viable offspring. The next section shortly explains this Penna model and then presents the minimal modifications which we found necessary to get sympatric speciation. A more realistic model involving three pairs of bitstrings instead of only one is discussed in the following section. We end with a short summary.