I'm a mere sprog, born as I was in '68, but I do recall big boys in the early and mid 70's had a craze for racers with chunky over-fat touring or commuting tyres, and cow-horn bars. The basic silhouette was certainly there.
And of course, who can forget the Highparths etc, true off road go anywhere machines, not just downhill clunkers, that can trace their lineage back to the 70's. Indeed, I'd give my left nut for a Highpath, though i should think they cost a few quid these days. In terms of true off roading they were perhaps the first, but like the Neanderthals, their lineage died out and a different branch of Homo-Offroadus came to the fore.