Historical clue formulations

• Existence — 2021-03-08
• Human ___ — 2017-04-10
• Organism — 2016-06-28
• Entity — 2015-03-22
• Life form — 2015-02-25
• Existence — 2014-11-11
• Extraterrestrial, e.g. — 2014-08-30
• Human or alien — 2014-06-01
• It's a state — 2014-01-31
• Subject for the philosopher Heidegger — 2013-12-01
• Human ___ — 2013-11-28
• Essence — 2012-05-30
• It's alive — 2010-04-23
• Life form — 2007-07-24
• It's alive — 2006-09-19
• With 69-Across, song from 20-Across — 2005-03-22
• Existence — 2003-02-04
• Extraterrestrial, e.g. — 2001-10-25
• Living thing — 2000-02-15
• Human or alien — 1999-12-23
• Life form — 1999-05-09
• Any one of God's creatures — 1999-01-11
• Existence — 1997-12-15
• Existence — 1996-04-17
• Since, colloquially, with "as" — 1996-02-18