Here’s a little history of saddle evolution, as summarized on the RP site.
I didn’t mention yet another reason I’m happy to promote info on the RP saddles. Here’s the policy of the company, they won’t sell you a saddle without you spending two weeks trying it out. This trial period is free, but you do need to pay for shipping if necessary. (You can lease it for longer if you need more time.)
I believe more companies are taking this or a similar approach these days, as more people are learning more about the science and art of saddle fitting. Never buy a saddle without a trial period, unless you’re willing to accept the risk that you may be stuck with a saddle that doesn’t fit, and have to resell it yourself. And remember, very importantly, that your horse may not tell you the first few days if it doesn’t fit. If the pressure spots aren’t too severe, if your horse is stoic, or if the pressure points are in different spots than the previous saddle, it may take a week or two of riding for soreness to show up.
All About Equine Massage 