In populations with a seed-bank, individuals can temporarily become dormant and refrain from reproduction until they can become active again. The repository of all dormant individuals in the... Show moreIn populations with a seed-bank, individuals can temporarily become dormant and refrain from reproduction until they can become active again. The repository of all dormant individuals in the population is called the seed-bank. Seed-banks are observed in many taxa, including plants, bacteria and other micro-organisms. Typically, they arise as a response to unfavourable environmental conditions. In this thesis we study the effect of a seed-bank on the genetic diversity in a population. The individuals in the population carry one of two gene types, live in colonies and can be either active or dormant. Active individuals can migrate between the colonies, resample and become dormant. Dormant individuals can only become active: they do not migrate and they do not reproduce themselves. The model is described by a system of interacting Fisher-Wright diffusions. Analysing this system of interacting diffusions, we show that the seed-bank enhances the genetic diversity in a population. If the individuals can become dormant for long enough times, the seed-bank can even prevent that a gene type becomes extinct. Show less
In this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time.... Show moreIn this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time. Representative samples of individuals from such populations are studied, focusing on individual opinions expressed on various topics, present in multivariate empirical data that had been previously collected, mainly via social surveys. We propose and exploit new methods for analyzing such data, relying on mathematical notions specific to statistical mechanics and information theory, but also on agent-based models/simulations of opinion/cultural dynamics driven by social influence. These methods provide new insights about how human culture is organized. They provide indications that cultural structure has universal properties, independent of the geographical region and of the set of survey questions. Furthermore, these properties suggest that culture is shaped around a small number of "rationalities", while also having a certain hierarchical organization that is robust to social influence dynamics. Finally, we propose a method of filtering the noise in the data, which seems to allow for the identification of cultural modules that are not visible otherwise. However, we also show that visible modules may well be just artifacts of survey design. Show less
