The practices of "thalikettu kalyanam", the polyandrous "sambandhams", and also the existence of large "tharavads" declined during the nineteenth century, as did that of hypergamy. Monogamy and small nuclear family units became the norm, as they were elsewhere in the country. This process occurred more rapidly in some areas than in others, and in Central Kerala the traditional systems still lingered as late as the 1960s, although hypergamy had largely disappeared everywhere by the 1920s. A possible reason for the various rates of change across the region lies in the extent to which the various agrarian local economies were dominated by the Nairs.