The mechanisms by which some animals are able to achieve astonishing feats of migration have often eluded researchers because of the difficulty of designing suitable experiments.
Rapid speciation resulted from post-glacial hybrid contacts and polyploidy during population migration have often been reported and documented.
Because these interspecies crosses utilized intact pistils, it has been impossible to discern the roles of individual tissues; moreover, early blocks in pollen tube migration have often made it difficult to assess interactions at downstream stages, including those near ovules.
"While the issue of illegal migration has often been cited as the sole reason for the present state of affairs in Assam, the reality on the ground is far more complex.
In contemporary studies, the vast body of literature on 'renewed' European East-west migration has often focused on analysing stocks and flows, on migration patterns, contributions to labour migration and integration (Guild & Mantu, 2011; Gabriel & Pellerin, 2008; Menz & Caviedes, 2010; Engbersen, Leerkes, Grabowska-Lusinska, Snel, & Burgers, 2013).
Yet the demographic literature on fertility and migration has often neglected to account for variation in migration characteristics in developing countries and often uses a simple binary measure of migrant/non-migrant (e.g., Brockerhoff and Yang 1994; Chattopadhyay, White, Debpuur, et al. 2006; Omondi and Ayiemba 2005; Oucho and Gould 1993).
However, seasonal migration has often been regarded as an adaptive strategy to increase growth and survival and, thus, to maximize fitness, in seasonally fluctuating environments [3].
While the state's migration policies have often been criticized as reactive, major bills and laws on migrant rights that have passed has shown how migrants together with various civil society groups and stakeholders can influence policy and lawmakers.
Efforts to reconstruct human origins and migration patterns have often focused on phylogeographic studies of the paternally inherited Y-chromosome and the maternally inherited mitochondrial DNA [16] [18].
Within the context of the global economic crisis, migration and integration policies have often been perceived as being both unpopular and superfluous (EUROCITIES, 2015; Ponzo et al., 2013).
Their migrations to the country towns have often left Aboriginal families as stranded "fringe dwellers," a term with social as well as geographic connotations.
