Hey!

Unfortunately, I am only an undergraduate student and I don't have expertise in that particular section of anthropology past introductory level. But the University of Alabama does have an online glossary for anthropology and this may be a good start for you.

www.as.ua.edu/ant/glossary.htm

tribe-A relatively small group of people (small society) who share a culture, speak a common language or dialect, and share a perception of their common history and uniqueness. Often refers to unstratified social groups with a minimum of (or no) centralized political authority at all, organized around kinship lines. (Hunter and Whitten, 1982)

a territorial population in which there are kin or nonkin groups with representatives in a number of local groups. (Ember and Ember, 1999)

ethnicity-The characteristic cultural, linguistic, and religious traditions that a given group of people use to establish their distinct social identity -usually within a larger social unit. (Hunter and Whitten, 1982)

Ethnicity is a multifactorial concept including, but not limited to, cultural constructs, genetic background, ecological specialization, and self-identification (Crews and Bindon, 1991).

Maybe you should start by looking up those authors. Good Luck!

If I understand correctly, there are tribal societies in which tribes prefer to select mates from outside the tribe, such as by trading females.
The larger society could be more-or-less genetically homogeneous as a result of this, even if the tribes have different laws, religious practices and linguistic variants.

i am a armchair anthropologist...when i read your post this is how it broke down in my mind.
i am part cherokee indian.supposedly. its hard to trace that sort of thing if you are not of european descent here in the us.
but you will notice that the tribe called 'cherokee' ranged throughout most of the southeast us, from about virginia heading on into sc,and ga,not so much florida. they were a large group of native americans sharing similar cultures,language and beliefs.when the europeans arrived and the fighting began& the drifting towards the midwest,smaller tribes ( what was left of them ) fleeing from from the ensuing slaughter and loss got sucked into the 'cherokees'...because they ( the cherokee ) were large enough to hold back the tide for a short while.
but even within the group of 'actual ' cherokees ' there where differences.the tribe was large enough to have them,such as the so called differences between southern Italians and the northern ones.
and no doubt these people were very similar,having very small differences.genetically, they were probably the same.
but they belonged to different 'tribes'...
you probably did not get much difference in skin color,height,build,hair texture,ect.
so the cherokee would be a ethnic group.while the creek indians would be a 'tribe',too small to be a culture all to itself.but still different from the larger ' cherokees'
no doubt the cherokees on the beach were different from the cherokees living in the appalachian mountains.
if i don't make sense,ignore me...i am on my third glass of wine.
hugs,
voudou

Perhaps you could use the ethnicity of Judaism for a measure. There is one ethnicity, labeled Jew. And there are twelve recognized tribes who all have a slightly different set of tribal rules within the original ground rules of the whole group.