> Why do we no longer have Renaissance men/women today, contributing to the sciences, philosophy and the arts? What did we lose?

A lot of the low-hanging fruit has already been claimed, and it's very difficult now for amateurs to make discoveries in mathematics and physics. There are people today doing amazing research, it just takes a career and a team (and in many cases expensive equipment) to do so.

If by "Renaissance men/women" you mean "well-versed/engaged in many topics", well, you just need to open your eyes. There are many folks like this now, likely millions. It was a bit more of a rarity a few hundred years ago, so it was much easier for these individuals to be documented/preserved.

The more complex (advanced) a society becomes, the more specialized its individual members have to become so the longer it takes to produce a unit for a specific function (basic education of people now takes 18 years of their life). With the exponential increase in scientific output (http://pespmc1.vub.ac.be/POS/turchFigs/IMG.FIG14.1.GIF) it becomes ever harder for an individual to keep up with multiple fields (in fact, I suspect that as soon as a field becomes _too_ big it automatically branches into new fields because of this).

It would have been possible to read every book in existence on mathematics in a lifetime in the 17th century, but not in the 21st century.

I'd wager that there weren't all that many renaissance men/women back in the day either, but some of the ones that were there are now well known.

In any case, there are plenty of people contributing in a wide array of fields who are alive today. How about Franklin Story Musgraves, who has academic degrees in six different fields, including medicine, computer programming and literature. He also went into space for NASA no less than six times, served in numerous conflicts while he was in the air force, was briefly employed as a mathematician for Kodak, practiced and taught clinical medicine and is/was a consultant for Disney. I found him with the briefest of google searches for "modern renaissance men" :)

https://en.wikipedia.org/wiki/Story_Musgrave