Whenever two or more unusual traits or situations are found in the same place, it is tempting to look for more than a coincidental relationship between them. The high Himalayas and the Tibetan plateau certainly have extraordinary physical characteristics, and the cultures which are found there are also unusual, though not unique. However, there is no intention of adopting Montesquieu's view of climate and soil as cultural determinants. The ecology of a region merely poses some problems faced by the inhabitants of the region, and while the problems facing a culture are important to its development, they do not determine it.
    The appearance of the Himalays during the late Tertiary Period and the accompanying further raising of the previously established rages had a marked effect on the climate of the region. Primarily, of course, it blocked the Indian monsoon from reaching Central Asia at all. Secondly, air and moisture from other directions were also reduced.
    Prior to the rising of the Himalays, the land now forming the Tibetan uplands had a dry continental climate with vegetation and animal life similar to that of the rest of the region on the same parallel, but somewhat different than that of the areas farther north, which were already drier. With the coming of the Himalayas and the relatively sudden drying out of the region, there was a severe thinning out of the animal and plant population. Then ensuring incomplete Pleistocene glaciations had a further thinning effect, but significantly did not wipe out life in the area. Thus after the end of the glaciations there were only a few varieties of life extant from the original continental species. Isolated by the Kunlun range from the Tarim basin and Turfan depression, species which had already adapted to the dry steppe climate, and would otherwise have been expected to flourish in Tibet, the remaining native fauna and flora multiplied. Armand describes the Tibetan fauna as not having great variety, but being "striking" in the abundance of the particular species that are present. The plant life is similarly limited in variety, with some observers finding no more than seventy varieties of plants in even the relatively fertile Eastern Tibetan valleys, with fewer than ten food crops. Tibetan "tea" is a major staple, perhaps replacing the unavailable vegetables.
    The difficulties of living in an environment at once dry and cold, and populated with species more usually hospitable climates, are great. These difficulties may well have influenced the unusual polyandrous societies typical of the region. Lattimore sees the maintenance of multiple-husband households as being preserved from earlier forms by the harsh conditions of the Tibetan uplands, which permitted no experimentation and "froze" the cultures which came there. Kawakita, on the other hand, sees the poly andry as a way of easily permitting the best household to become the head husband regardless of age. His detailed studies of the Bhotea of Tsumje do seem to support this idea of polyandry as a method of talent mobility is a situation where even the best talent is barely enough for survival.
    In sum, though arguments can be made that a pre-existing polyandrous system was strengthened and persevered (insofar as it has been) by the rigors of the land, it would certainly be an overstatement to lay causative factor of any stronger nature to the ecological influence in this case.  What are the "unusual traits or situations" referred to in the first sentence?