A major outcome of multi-generational natal philopatry is genetic divergence and, ultimately, speciation. Without genetic exchange, geographically and reproductively isolated populations may undergo genetic drift. Such speciation is most evident on islands. For mobile island-breeding animals, finding a new breeding location may be beyond their means. In combination with a small population, as may occur due to recent colonisation, or simply restricted space, genetic drift can occur on shorter timescales than is observable in mainland species. The high levels of endemism on islands have been attributed to these factors.