Sociologist: Climate and geology determine where human industry can be established. Drastic shifts in climate always result in migrations, and migrations bring about the intermingling of ideas necessary for rapid advances in civilization. The sociologist's statements, if true, most strongly support which one of the following? ['Populations settle in every place where human industry can be established.', 'All shifts in climate produce a net gain in human progress.', 'Climate is the primary cause of migration.', 'A population remains settled only where the climate is fairly stable.']