C.C. Uhlenbeck made a distinction between two components of Proto-Indo-European, which he called A and B (1935a: 133ff.). The first component comprises pronouns, verbal roots, and derivational suffixes, and may be compared with Uralic, whereas the second component contains isolated words, such as numerals and most underived nouns, which have a different source. The wide attestation of the Indo-European numerals must be attributed to the development of trade resulting from the increased mobility which was the primary cause of the Indo-European expansions. Numerals do not belong to the basic vocabulary of a neolithic culture, as is clear from their absence in Proto-Uralic (cf. also Collinder 1965: 112) and from the spread of Chinese numerals throughout East Asia. Though Uhlenbeck objects to the term “substratum” for his B complex, I think that it is a perfectly appropriate denomination.