The indefinite pronouns of a language are derived from generic nouns.  This is the case in English, in which the indefinite forms "somebody/someone" and "something" clearly derive from generic nouns denoting "person" and "thing."

<br><br><b>Reference</b><br>
Haspelmath, Martin. 2008. Indefinite Pronouns.
In Haspelmath et al (2008), chapter 46. Available online at <a href="http://wals.info/feature/46">
http://wals.info/feature/46</a href>.
