> Can you have PhD in arts or post modern philosophy? Does that require high IQ?
Yes, and yes for the latter. Philosophy is my own field, and while I would be much more comfortable making this assertion of analytic philosophers, post-modern (I'll assume you really mean 'continental') philosophers are still very smart people.
Since you aren't doing any research, I will do just a little, and point out that philosophy PhDs tend to have been philosophy majors, and philosophy majors tend to have extremely high GRE scores, and the GRE is extremely correlated with IQ; philosophy majors are #1 and beat every other major when it comes to the Verbal and Analytic Writing sections - surely not the work of people of average intelligence - and rank 15th out of 50 in math scores (ahead of majors such as biology, accounting, architecture and others; being beaten by various engineering, physics/astronomy, and math majors): http://www.ncsu.edu/chass/philo/GRE%20Scores%20by%20Intended...
> Not every book from back then survived.
Yes, but many catalogues (the Suda eg.) and quotes have survived. The survival rate and biases introduced by history can, and have been, estimated. (The latest one I heard about used statistics about the survival of works of the Venerable Bede, but I can't find the citation in a quick google.) The bias is not orders of magnitude, though it hits some authors badly (Sophocles's prize-winners, eg.) as one would expect from a random process.
Yes, and yes for the latter. Philosophy is my own field, and while I would be much more comfortable making this assertion of analytic philosophers, post-modern (I'll assume you really mean 'continental') philosophers are still very smart people.
Since you aren't doing any research, I will do just a little, and point out that philosophy PhDs tend to have been philosophy majors, and philosophy majors tend to have extremely high GRE scores, and the GRE is extremely correlated with IQ; philosophy majors are #1 and beat every other major when it comes to the Verbal and Analytic Writing sections - surely not the work of people of average intelligence - and rank 15th out of 50 in math scores (ahead of majors such as biology, accounting, architecture and others; being beaten by various engineering, physics/astronomy, and math majors): http://www.ncsu.edu/chass/philo/GRE%20Scores%20by%20Intended...
> Not every book from back then survived.
Yes, but many catalogues (the Suda eg.) and quotes have survived. The survival rate and biases introduced by history can, and have been, estimated. (The latest one I heard about used statistics about the survival of works of the Venerable Bede, but I can't find the citation in a quick google.) The bias is not orders of magnitude, though it hits some authors badly (Sophocles's prize-winners, eg.) as one would expect from a random process.