Gensim API implements a combination of the genetic algorithm (https://en.wikipedia.org/wiki/Genetic_algorithm) and some assumptions regarding expected fluctuations in traits not specifically linked to genetics e.g. height. This allows gensim to realistically simulate actors in simulations breeding with one another and slowly evolving as they do so. A child's traits are usually a combination of their parents with the aforementioned flucuations where applicable. That being said, according to the genetic algorithm there is a 0.6% chance for a random mutation to occur. This random mutation is currently just a change in an existing trait but I would like to add the ability for new traits to emerge such as sexual desireability etc.