According to -- http://en.wikipedia.org/wiki/Michael_Shermer -- Michael Shermer wrote this in his 2002 book Why People Believe Weird Things: "I became a skeptic on Saturday, August 6, 1983, on the long climbing road to Loveland Pass, Colorado after months of training under the guidance of a 'nutritionist' with an unaccredited Ph.D."
However, according to -- http://www.advunderground.com/interviews/2007/shermer0107.php -- this exchange took place earlier this year between Logan Kaufman and Michael Shermer:
Logan: "When did you first become what you would consider a skeptic? Was there a defining moment or did your general philosophy evolve with time?"
Michael Shermer: "No particular defining moment, but an evolution over time of my critical thinking skills, honed by scientific training, applied to more and more topics."
So, I guess Shermer's "critical thinking skills" have indeed undergone an "evolution over time."
However, according to -- http://www.advunderground.com/interviews/2007/shermer0107.php -- this exchange took place earlier this year between Logan Kaufman and Michael Shermer:
Logan: "When did you first become what you would consider a skeptic? Was there a defining moment or did your general philosophy evolve with time?"
Michael Shermer: "No particular defining moment, but an evolution over time of my critical thinking skills, honed by scientific training, applied to more and more topics."
So, I guess Shermer's "critical thinking skills" have indeed undergone an "evolution over time."