Bekhorot 4: Wilderness First-borns

A new mishnah! Establishing additional exemptions for the first-born donkey offerings. The initial exemptions took place in the wilderness, and exempted the Levites, because the people themselves were going to be exempted. But other - kosher - animals were still subject to the laws of the first-born (cattle, sheep, and goats). But why are the Levites exempt from the first-born son and the first-born donkey, but subject to the regular, other animals' first-borns? Also, the first-born sanctification seems to have first taken place in the wilderness -- or were they not? (A dispute between R. Yochanan and Resh Lakish) Note the original role of the first-born (people), before the kohanim were selected for their role. Then, the sanctification of the first-borns made a different kind of sense.