"For more than 50 years, men and women around the world have reported sights in the sky that are strange to their experience and understanding. Inasmuch as many of these sights appeared to be solid objects having impressive performance, they have become known as Unidentified Flying Objects (UFOs) or, colloquially, flying saucers. Their positive identification is one of the major public scientific challenges of the era, with a significant number of these sights so far defying all reasonable efforts at classification."

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It is clear, from these considerations, that the three methods of classifying mankind-that according to physical characters, according to language, and according to culture-all reflect the historical development of races from different standpoints; and that the results of the three classifications are not comparable, because the historical facts do not affect the three classes of phenomena equally. A consideration of all these classes of facts is needed when we endeavour to reconstruct the early history of the races of mankind.

— Franz Boas