All the ones I know have advanced most with practice and life experience above all, not formal instruction. And by far not all who have received instruction are doing well (producing work in high demand) post-instruction.
All the artists, writers, etc. I know who have advanced the
fastest did so by getting formal instruction (a BFA or MFA, or going to a music conservatory or equivalent drama school). The only exception among those I know is one who pursued the old fashioned version of that, namely, apprenticing with an accomplished artist in Italy. Getting intensive training is to the arts what spending 2-3 years living and working or studying in a foreign country is to language learning.
It's total immersion and it enables far more development than you're likely to get in the same time period any other way.
Just read one of the many recent obituaries of Peter O'Toole to see what a few years at the Royal Academy of Dramatic Arts did for him. It took a penniless teenager with only two or three years of formal schooling (of ANY kind, including elementary school), who came from "the criminal classes" as he put it (a poverty-stricken ghetto--his dad was a grifter and several of his childhood friends spent their adult lives in prison, some for murder), and turned him into one of the most polished, sophisticated, talented stage and film actors of his generation.
And I'm sure O'Toole had classmates whose careers didn't fare nearly as well, just like many people with BFAs, MFAs, conservatory degrees, etc. But I also know plenty of engineers whose careers are average at best.
That's just the nature of life: in any field, some people will meet with spectacular success, some will fail, and most will do about average. At least an artist with formal training is qualified to become a teacher of their art--and is that not a perfectly respectable career?
My initial wording was 'how many society can support." At one time, we could support no artists or scholars of any kind because everyone had to work on acquiring food and shelter. There was simply no man-hours left after hunting, gathering, and protecting children from sabertooth tigers.
Jrez is correct on this. When exactly was this, do you think, that homo sapiens didn't have artists? There's a growing body of evidence that even Neanderthals made art, at least later in their history, and Cro Magnons (aka anatomically modern humans, who appeared in Europe about 43,000 years ago) have been using pigments and carving non-functional things (i.e., making art) for as long as we've existed.
"Extremely old, non-representational ornamentation has been found across Africa. The oldest firmly-dated example is a collection of
82,000 year old Nassarius snail shells found in Morocco that are pierced and covered with red ochre.... The oldest known representational imagery comes from the Aurignacian culture of the Upper Paleolithic period. Archeological discoveries across a broad swath of Europe (especially Southern France, Northern Spain, and Swabia, in Germany) include over two hundred caves with spectacular Aurignacian paintings, drawings and sculpture that are among the earliest undisputed examples of representational image-making. The oldest of these is a 2.4-inch tall female figure carved out of mammoth ivory that was found in six fragments in the Hohle Fels cave near Schelklingen in southern Germany. It dates to
35,000 B.C.E."
http://smarthistory.khanacademy.org/origins.html"Prehistoric dots and crimson hand stencils on Spanish cave walls are now the world's oldest known cave art, according to new dating results—perhaps the best evidence yet that Neanderthals were Earth's first cave painters.... At
more than 40,800 years old, "this is currently Europe's oldest dated art by at least 4,000 years," said the study's lead author..."
http://news.nationalgeographic.com/news/2012/06/120614-neanderthal-cave-paintings-spain-science-pike/"Pendants made from these [eagle] claws have been found at numerous sites in France and Spain spanning nearly 60,000 years. Some of the latest Neanderthal sites turned up modified and sometimes pierced tooth and bone pendants and other art objects."
http://www.nytimes.com/2013/05/03/opinion/global/Who-Are-You-Calling-a-Neanderthal.html