A study of the physical types has shown that each group considered is made up of heterogeneous elements.  Pigmy blood is everywhere evident, but aside from this there is a well-marked brachycephalic and a dolichocephalic element.  With the latter is a greater tendency than with the first for the face to be angular; the cheek bones are more outstanding, while there is a greater length and breadth of the nose.  Individuals of each type are found in all the groups considered, but taken in the average, it is found that the Ilocano and Valley Tinguian fall into the first or round-headed class, the Bontoc Igorot are mesaticephalic, while between them are the mountain Tinguian and Apayao.

Judging from their habitat and the physical data, it appears that the Igorot groups were the first comers; that the brachycephalic Ilocano-Tinguian arrived later and took possession of the coast, and that the two groups have intermarried to form the intermediate peoples.  However, a comparison of our Luzon measurements with the people of southern China and the Perak Malay leads us to believe that the tribes of northwestern Luzon are all closely related to the dominant peoples of southern China, Indo-China, and Malaysia in general, in all of which the intermingling of these types is apparent.

The dialects of northwestern Luzon, while not mutually intelligible, are similar in morphology, and have a considerable part of their vocabularies in common.  Here again the Igorot is at one extreme, the Ilocano and Valley Tinguian at the other, while the intervening groups are intermediate, but with a strong leaning toward the coast tongue.

Considering, for the moment, the Bontoc Igorot and the Tinguian, it is found that both have certain elements of culture which are doubtless old possessions, as, for instance, head-hunting, terraced rice-fields, iron-working, a peculiar type of shield, and a battle-axe which they share with the Apayao of Luzon and the Naga of Assam.

A part or all of these may be due to a common heritage, at any rate, they help to strengthen the feeling that in remote times these peoples were closely related.  But a detailed study of their social organizations; of their ceremonies, songs, and dances; of their customs at birth, marriage, death, and burial; of their house-building; as well as the details of certain occupations, such as the rice culture, pottery making, and weaving, indicates that not only have they been long separated, but that they have been subjected to very different outside influences, probably prior to their entry into the Philippines.