Their highest peaks exceed 4,000 meters.

Their passes, while crossable in summer, are blocked by snow and ice for significant portions of the year.

The valleys between the major ranges are often narrow, steep-sided, and difficult to traverse.

The terrain is fundamentally different from the broad plains of northern and central Europe, where populations could and did move freely in all directions.

The research team’s finding that Ötzi’s genome showed the effects of genetic isolation — less hunter-gatherer ancestry than most other contemporaneous European populations, less mixing with the populations to the north and west — suggests that the Alpine topography had a measurable genetic effect.

Communities living in Alpine valleys had less contact with communities outside the Alps than the populations of the surrounding lowlands had with each other.