The word sapiosexual describes one who is attracted to intelligence. And while it's formed from Latin roots (sapiens + sexual), it appears to be a very new word.
Google Ngram has no record of the word prior to 2008 (the most recent search available).
The Online Etymology Dictionary doesn't know about it.
Wiktionary offers half a dozen quotes, the earliest one from a usenet post in 2005, and all others post-2010.
What is the earliest known usage of this word?
Best Answer
Below is an excerpt from the usenet link the OP provided:
Thu, 20 Oct 2005, 10:43:13
Newsgroups: alt.polyamory
It's clear that the term sapiosexual was already well known and used among ‘geeks’ in 2005.
The © 1999-2015 Urban Dictionary ® entry has proved to be useful benchmark. It is dated December 05, 2002
Nine months earlier, on March 14 2002, a blogger called Jadine left the following entry on Live Journal; a social-network cum blogging platform, created in 1999.
The user mentioned by Jadine is Torin/Darren WhoEver (aka Wolfieboy), who started using Live Journal September 5th, 2001. Is this the same Darren Stalder from Urban Dictionary? It would appear to be so.
March 15 2002, 12:24:00
[Emphasis mine]
EDIT:
I've done my best to triple-check everything. The entry dated March 14 2002 is the earliest instance of the expression sapiosexual I found on the web.
For example, if you narrow the search dates between 1/1/1999 and 12/31/2000 Google yields only one result, a blogger on tumblr. But Tumblr was launched in 2007. Changing the dates between 1/1/2000 and 12/31/2001, produces links ALL dated January 31 2001 and they are either from tumblr, pinterest, twitter, pinsta accounts etc. None of these social networks existed in 2001. Note the link I posted is found on page 14 of Google.