The ecological diversity and the differential cultural adjustments of particular populations to their effective environment both physical and natural, have led to the evolution of at least 77 major ethnolinguistic groups in the Philippine archipelago. These groups are compounded by their own respective subgroups numbering about 244 with their own variations of the central cultures. Ecotonal areas have also given rise to marginal populations where culture change is much more accelerated than the core areas.

The diversification is not only dispersed horizontally in the various regions, but also vertically, with respect to the different elevations of the habitation areas of the groups. This has become so since changes in elevations in the topography produce differences in climatologically affected flora and fauna. Various parts of the country, too, are affected differentially by the wind currents that flow over the archipelago seasonally, principal among which are the southwest monsoon, the northeast monsoon, the southeast and the Siberian current. Those that are affected directly by the monsoons exhibit distinctive flora; others that are not so affected develop differently. Ecological zones, too, differ in terms of elevations. The edge of the sea develops mangrove forests. Dipterocarp forests cover vast tracts of land. Higher up are the mountain forests characterized by tropical oaks. Beyond these are the temperate zone forests where the temperatures are brought down by the increased elevation. And much higher still are the mossy forests. Societies change since cultures adapt to the vagaries of the physical environment, adjusting their subsistence patterns to the relevant features of the environment. In all these, differentially developed ecosystems are niches where ethnic groups coevolved correspondingly different culture complexes.

Due to the generally homogeneous forms of ecosystems prevalent in some broad areas, and the relatively more increased interaction between ethnic groups that inhabit proximate areas, some patterning of culture may be seen in certain regions in the Philippines. Thus, the mountain regions of the Cordilleras of Northern Luzon have peoples that appear to be related in general aspects of their culture as the Ifugao, Bontoc, Kalinga, Ibaloy, Kankanaey, Apayao, Itneg, and Gaddang. In the Cagayan Valley, between the Cordilleras and the Sierra Madre Mountains, adaptation is again specialized giving rise to the cultures of the Ibanag, Itawis, and Yogad. Influenced by the Islamic movements and provided with a base Southeast Asian culture the southwestern part of the Philippines forms another generalized grouping of similar cultures: the Tausug, Maranao, and Maguindanao. The peoples of the central and eastern Mindanao are yet to exhibit another set pattern, like the Manobo, Mandaya, and T’boli. Central Philippines and the other lowland and coastal areas all exhibit a leveling of culture such that homogeneity is more the rule.

An enigma in itself is the widely distributed groups of Negrito who, in spite of isolation from one another, exhibit similar features in their culture. In the hinterlands are small groups that subsist largely through food-gathering activities. The similitude, however, is deceptive for each group is very well defined and distinct, differentiated in their resources and habitat and as far ranging in variations as their Austronesian languages.

More than geographic and environmental circumscription are the social boundaries that separate one group of people from another. From the basic biological unit of parents and children, the more sociologically operable unit composed of the household extends the concept of family, as the former forms the basic economic, social and ritual unit— the household. The composition of this unit is defined by each society and it may range from a single individual to more complex families composed of a number of nuclear members. In some societies, a household of only one member is considered an effective and operable unit so long as this single member fulfills all the obligations to the society of a family member, that is, it performs all the functions-subsistence, social, ritual, and others — usually attributed to a full-fledged family.

Usually, households are bound together into a more or less cohesive aggrupation based on kin relationships of some kind in varying degrees of distances in consanguinity or affinity, gravitating around the household of a senior member, e.g., households of children establishing postmarital residences about a parent of either side. Groupings like these are further increased in scale by the gathering of kindred, which greatly enhances the spread of sociological benefits horizontally among peer groups, as in the polarization of social groups in confrontational situations. The relationships between such groups, however, can redound into one of a more cohesive nature as alliances develop where the canalization of behavior becomes more of a pattern than a divergence. In such instances the emergence of a strong personality would weld such alliances into a political structure, some initially based on reciprocity and redistribution of benefits.

Ethnic groups become marked also by means of which inheritances are distributed among the members. While the general rule of kinship is an equal reckoning of affiliation on both parents, there are differences in the manner by which property is treated upon the death of parents. In the Cordilleras, for instance, it is the oldest child that inherits the property, but he is also under social sanctions to support his siblings. In much of the lowland areas the inheritance is more equally distributed among the offspring. This is so because in the highlands, arable land in the rugged environment is a premium commodity that cannot be continually subdivided and reduced down the line of descent, whereas in the lowlands this is not usually the case since agricultural land here is more expansive. Since social proximities and distances lead groups to invert into themselves to the exclusion of others, the environment in which they find themselves tends to be homogenous for all the members.

The manner by which the members adapt to the parameters of the environment in terms of subsistence technology is usually common to all. Thus, along the shoreline communities tend to be fisherfolk, and in the uplands the subsistence pattern develops along the lines of slash-and-burn cultivation, and so on. The domestic kind of economy practiced would be one where each household is both the producing and the consuming unit. Without the generation of a surplus in the production, there is little need for a market, if there is one at all, where the existence of specializations in the production of goods would lead to the need to trade for things one household does not produce.

Religion, too, is a powerful organizing principle that defines the edges of an ethnic group. The communities may be organized based on any number of parameters. One of this would be based on the circle of members that constitute a “parish.” The parishes of ritual specialists are sharply confined to specific groupings of individual households. The linkages may be based on kinship network or more intimate personal associations, or simply, the structure of the religion itself limits the membership.

In some areas in the Cordillera, for instance, the ritual specialist will only celebrate the rituals of a particular grouping of households whether or not these belong to a contiguous group. The membership is traced to the extent of the meat-sharing system that is part of the ritual feast that highlights a celebration. Outside the network of households and individuals that shared the meat of animals sacrificed, membership to the community stops. There are overlaps in particular meat-sharing networks. Those that do not belong to any of these networks will not be part of the ethnic group.