Evolutionary genetics is the study of how evolutionary changes occur due to genetic variations. It includes topics such as the evolution of genome structure, the genetic basis of speciation and adaptation, and genetic change in response to selection within populations. Evolutionary genetics is the broad field of studies that resulted from the integration of genetics and Darwinian evolution, called the modern synthesis. This field attempts to account for evolution in terms of changes in gene and genotype frequencies within populations and the processes that convert the variation with populations into more or less permanent variation between species. Four evolutionary forces (mutation, random genetic drift, natural selection, and gene flow) acting within and among populations cause micro-evolutionary change and these processes are sufficient to account for macro-evolutionary patterns, which arise in the longer term from the collective action of these forces