Historically, Nairs lived in large family units called "tharavads" that housed descendants of one common female ancestor. These family units along with their unusual marriage customs, which are no longer practiced, have been much studied. Although the detail varied from one region to the next, the main points of interest to researchers of Nair marriage customs were the existence of two particular rituals—the pre-pubertal "thalikettu kalyanam" and the later "sambandam"—and the practice of polygamy in some areas. Some Nair women also practiced hypergamy with Nambudiri Brahmins from the Malabar region.