Cool Jeffries quote I found: ‘When I retired back in 1904 a lot of experts claimed I was unbeatable - that I was just naturally so big and fast and tough and strong that there was no use expecting any other fighter to beat me. I never did agree with that. I was not a 'natural'. I was a 'made' fighter. The night I fought [Bob] Fitzsimmons for the title I was 24 years old, weighed better than 200lb, could run the hundred in under 11 seconds, and could do the standing high jump to the height of my shoulders. I fought from a crouch that made it hard to hit me where it hurt. Fitz was the greatest body puncher there was, but he wrecked his hands on me that night. I fought with my left hand extended, and I had a knockout in it that never travelled more than a few inches. But how much of that could you call natural? It was no more natural for me to run the hundred barefoot in 11 seconds than it was for any other 200-pounder. I'd worked for years to build up that speed. The crouch and that left hand weren't natural: I'd spent hundreds of hours of drilling, trying out this idea and that, sweating my head off and taking plenty of punches before I had them readied up for a man like Fitzsimmons. I trained like a horse. When I didn't train - well, I went in untrained against Jim Corbett once, and he boxed the ears off me for 23 rounds before I finally got to him. It wasn't just natural for me to lick the other boy. If I'd been a natural-born fighter I might have been a kiIIer in the ring - I had the strength of it. But thank God I didn't have that temperament. I only once went in the ring angry, wanting to hurt the other fellow. I only once tried to hit the other boy as hard as I could - and that time I missed. I worked out in training with the roughest fighters I could hire, but I never in my life knocked out a sparring partner, and never tried to. I fought only one preliminary in my career, and I got to the top in ten starts after that. The record book makes it look quick and easy - like I was some kind of ring wonder. But the work I did doesn't show in the book. I fought my first pro fight when I was 16 years old, and I put in eight years of the toughest kind of plugging before I got my shot at the title. The plugging don't show in the record book, but I did it.' https://www.facebook.com/share/p/184UzEN11d/?mibextid=wwXIfr
He certainly has all the signs of having been a physical outlier, that guy you see in the gym once in a very long while who was far stronger than he even looked (and Jeffries looked very strong), who could do things that just seemed ridiculously beyond what would be expected. That's a lot of raw material that could have been applied in any era, probably with a different style, different fighting approach. The learned part can be changed. The raw material can not.