https://en.m.wikipedia.org/wiki/Jet_fighter_generations

Using the "generations" term like is used to define the different innovations of jet fighters, what generation number would you assign to the modern pistol, and what separates each generation?

I would think the ability to mount lights and lasers, suppressors and optics have had roles in advancing the stages, as would modularity. But would you lump all that together as one or would you separate them by the times each was introduced or became standard options?

Discuss

Eh.  Super debatable but maybe something like:

1) Luger, C96 etc (although you could also call these 2nd or 3rd Gen and start earlier or with other contemporaneous different designs)

2) 1911, BHP, etc

3) Walther P38, PPK, CZ75, SW59

4) Glock 17, HK USP, etc

4.5) rails, backstraps, red dots etc

Two. pre-metalic cartridge, and metallic cartridge. 
A subset of metallic cartridge is revolver and semi-auto. 
A subset of semi-auto is browning tilt barrel, and everything else. 

One could make a case for generations, but most modern guns are re-hashes of late 1800's, early 1900's guns. (or never built designs) 

Tech forum - Maynard

Blowback is first gen.
Then toggles, etc.
Browning link.
Browning style with ramp and locking shoulder in the ejection port.
Modular trigger assembly that isn't pinned to the frame.

Now where to put the HK P7? It's delayed by gas, so at least second generation. It has a unique cocking action, which could bump to third. And then how does the 1911 compare to the Walther P38 or Browning HiPower? Sorry, but its not the same generation, it's earlier and less sophisticated. For one, it actually uses a moving link instead of ramps, and it locks inside the slide with precision fitted slots instead of against a chamber shoulder into the ejection port.

A lot of these generational improvements are also about fabrication and manufacture. Guns are actually simpler now than they have been. And polymer frames can't be ignored. It comes down to the SIG P320 being the most advanced at present. At a bid price of $207 it's a very strong competitor - haven't heard of the 1911 being bid that low in a contract lately, it simply can't be with the extensive machining.

Looking forward to more input.

To look at pistol evolution as generations you will never get a good sense of how things progressed.  You would need to look at it more as a family tree of evolution because some incorporated one design and others followed other paths and some you can trace certain aspects to other pistols but others were complete revolutionary.

I'd start with gen 0, which featured all kinds of goofy operating systems, magazine placement, etc (think broom handles, lugers, borchart, etc) along with complicated assembly/disassembly. These guns were the proof of concept for what would follow.

Then I'd call gen 1 the age of the steel frame, basically starting with the 1911 and it's immediate precursors. Reliable, simple, effective handguns. Due to materials and manufacturing technologies, they are hard/expensive to make today, but these guns were revolutionary, and while obsolete, are not "that" obsolete. Still perfectly serviceable firearms. I suppose I'd put other guns like the higpower here, though you could arguably call it a new generation for the doublestack magazine. While still expensive to make and sharing a lot in common with the 1911, it is essentially the dawn of the modern wonder 9. I would also throw in the CZ75 and similar pistols. 

In my opinion, nothing has really changed since the Browning hipower and 1911 as far as the basic operation of the pistol. Even the evolution of striker fired guns dates way back. IIRC, the original prototype hipower was striker fired. I would say the main advancement for "gen 2" is materials science and manufacturing technology. We can now make guns that are as reliable as well built guns of yesteryear every single time, cheaply. I'd put the Glock 17 as one of the founders of this generation. I might also put aluminum framed guns in this category. The basic mechanics are the same operating principles as the 1911. 

I think gen 3 is the ability to put reliable optics, flashlights, lasers, etc on the guns. 

I would agree with a lot of this as well, and as others have mentioned nothing in pistol design is at all new. Striker fired has been around since around 1900, tilting barrel locking systems about the same. Polymer frames since the 1970's and bullseye shooters started mounting red dots in the 1980's. Beyond that using glock as the typical example, glock simply decided what were the most positive aspects of a multitude of designs and married those features to the companies pre existing mass production methods.
Having been in the game myself almost 1/2 a century now, personally I think the biggest leap forward in pistols is having a large number of pistol choices proven to run Reliably with high performance hollow point ammo. I still recall the days having a reliable semi was considered rare and one that was with hollow points equal to a golden egg

If you can step back from it and consider auto-loading handguns only, I think the answer will be similar to 'Madcaps'; basically you have pre and post-1911. Even the current rave of polymer-frame striker-fired pistols is not really anything new except for the use of polymers. The Luger was striker-fired. Even gas-delayed blowback actions, while innovative, are not really necessary. There's nothing really new under the sun. You have a metallic cartridge with a primer, propellant and a projectile. They all work the same way, the recoil knocking the slide back to remove the spent shell and cock the action while the recoil spring slams it home again to strip a fresh round off the magazine and shove it into the barrel chamber. Plus, nearly all the various types of actions and designs invented since about 1900 are still in production! You can't have 'generations' of anything with all the types still in production (notable exceptions are the Luger and its predecessors, which AFAIK are not being made anywhere at this time).

Four.