a lot of 'probably' in there.
Yup, there's never certainty in science. There's also uncertainty in your and my guesses. It will be interesting to see what future scientific investigation reveals.
I'm not suggesting for a minute that they grazed on grass. But while hunting or foraging, chewed on especially spring grasses, just as I and many other's have done,,
Do you mean that probably not a lot in the way of grass blades was wholly grazed/consumed, instead just the occasional chewing/sucking of some grass stalks here and there, and the food focus was more on the tubers and possibly also the seeds? If so, I agree that that's more likely--especially the tubers, it seems, based on the research I cited above and other research and the experience of myself and others.
I still have not seen evidence that any fibrous material with sugar or starch, making it to the large intestine isn't food for these bacteria, just as grass does for cows. That is why I've said several times, that pieces of lettuce, seaweed, corn, carrot, the fibrous parts of oranges or other fruits, nuts, etc. anything with starchy fiber potentially can feed these fatty acid producing bacteria. If you know from literature or experience otherwise, please let me know. And suspect anyone not strictly trying to go as close to Zero Carb as possible are being provided quite a host of foods for their guts.
By "sugar", do you mean fruits? I believe the primary fermentable prebiotic they contain is pectin. Sugars themselves (sucrose, glucose, fructose, galactose, maltose and lactose) are not normally classed as prebiotics, as they are mostly digested in the mouth, stomach and small intestine, rather than the colon.
Do you mean that there are other prebiotics beyond resistant starch (RS isn't yet technically classed as a prebiotic, but for simplicity's sake I'll use that term for all foods that feed gut bacteria), such as inulin, that are also converted into butyrate? If so, I agree with that and I've indicated that myself in the past. It was never about just RS and all the prebiotics are hypothesized to be beneficial in one way or another, even those that don't contribute to butyrate production. Whether they all are or not and to what degree is not written in stone and is a matter for future further investigation.
It seems that RS may have been especially impactful among prebiotics for me and hundreds of other LC Paleo dieters because it's the one that tends to get most thoroughly excluded in such diets. That doesn't mean that the others aren't also important, just that they don't tend to get excluded as severely, from what I've seen, and they also don't tend to be as controversial. Ironically, the passionate backlash against RS only served to further draw attention to the topic at multiple blogs and forums. The primary source of the passion seems to be the word "starch," which seems offputting to many VLCers, perhaps because "starch" was so thoroughly demonized in the past (and another major uproar occurred when Paul Jaminet started using the term "safe starches"--he was criticized by a host of LC gurus, despite himself advocating a LC diet). As a result, at times the voluminous discussion about RS may seem like RS is the sole focus, but that was never the intention.
Hope that clears things up some.
Interestingly, yet another prominent LCer has started writing positively about RS and other prebiotics--Dr. William Davis, author of Wheat Belly:
http://www.wheatbellyblog.com/2014/07/fertilize-garden-called-bowel-flora/He joins, Mark Sisson, Tom Naughton, Richard Nikoley, Paul Jaminet, Norm Robillard, Chris Kresser, Dr. Jack Kruse, Prof. Stephan Guyenet, Melissa McEwen and other current and former LCers (I think they all at least tried LC or VLC at some point in their lives, if I'm not mistaken) who have written at least something positive about prebiotics. As these and other folks write more and more positive stuff about prebiotics and more and more positive reports are shared at their blogs and elsewhere, and more and more research is published showing benefits from prebiotics and that they were included in ancestral diets, I'm noticing less and less negative comments about RS and other prebiotics from the fans of these folks and LCers in general. I'm not expecting Dr. Ron Rosedale, Dr. Richard Bernstein or Ray Peat (who's not a LCer, but seems to have a basically low opinion of prebiotics) to follow suit any time soon, though, but who knows, anything can happen. Heck, even Jimmy Moore said he's going to try experimenting with RS.
No doubt, more folks will also go overboard with RS and other prebiotics, as seems to happen with everything.