Taxonomy (the technique of classification is a science, but in practice, it becomes a lot trickier. Recall only a couple years ago when Congress notoriously chose to classify pizza in school lunches as a vegetable item. This was a convenient classification because pizza provided a grain serving and was smeared with tomato sauce—tomatoes being a vegetable as well. Or are they? In a case that reached the Supreme Court, despite clear definitional evidence that tomatoes are indeed fruit (they grow from the seed of a flowering plant), decided that the tomato was a vegetable, and therefore that the tomato would be treated under vegetable tariffs. All this because even back in 1893 (the case was called Nix v. Hedden, by the way), the tomato was used in cuisine as more vegetable than fruit. Practicality trumped orthodoxy, and it became, legally, a vegetable.
For religions, taxonomy can not only be a matter of tariffs and health standards, but of sin. The books of Leviticus and Deuteronomy contain dietary guidelines for that many Jewish faiths follow. More specifically, the Bible forbids consumption of certain foods made from grains like wheat, barley, and oats on Passover. When Jewish communities, through trade, encountered new grain-like foods such as rice and corn, they decided that those two applied under the Biblical laws, even though they were not outlawed.
The ultimate example, though, comes courtesy of the Catholic Church in the 17th century. With missionaries spreading across the New World and discovering all sorts of new foods (like—hey!—corn and tomatoes). These new foods also included, particularly for French-Catholic trappers in Canada, beavers. Though hunted primarily for their pelts, beaver meat was also a part of both Native and European pioneer’s cuisine.
But when it came to Lenten season for Catholic practioners, they were barred from eating meat, ostensibly including beaver. With lobbying from the Quebecois Church, Catholics applied this deft analysis: since beavers occupied the rivers and streams of North America, they fall under the category of fish, and therefore could be consumed during Lent. And thus, mammalian swimmers (including, for South American Catholics, the capybara) became fish.
Huzzah! Yet another theological problem solved by the deft thinkers of 17th century Rome. Anyway, they seem to be pretty cute animals, check out a couple baby beavers below.
“When the Catholic Church decided beavers were fish,” Jason G. Goldman, Salon via Scientific American