That is a very good point. Pre-agriculture, we have to accept that plant food was simply  not as widely available all year round.
There is also a similiar argument used by Weston-Price advocates:- namely that since certain ancient hunter-gatherer tribes ate certain foods, that that fact made those very foods fully  acceptable to modern humans, conveniently forgetting the fact that in palaeo times, megafauna etc. existed that perished well before  the Neolithic era.

Humans who are desperate will eat almost anything, however unhealthy. For example, several tribes have regularly eaten plants rich in cyanide such as cassava as part of their diet.
Geoff



> Date: Fri, 1 Jan 2016 11:53:44 -0600
> From: [log in to unmask]
> Subject: Re: Paleo Fibre
> To: [log in to unmask]
> 
> Let me finish this thought with a bit of an extreme example.  Just because a particular population may have regularly ingested cyanide, doesn’t ipso facto make cyanide good for humans.  The paleo standard has always seemed to me to be the types and classes of foods that humans consumed over the vast majority of our time here on earth.  Individual populations may have adapted to a wider range, including certain grains for instance.  But it seems to me you can’t go wrong with that definition of the paleo standard.  How you then go on to define then what it is that we’ve eaten is of course the more interesting problem.  Did we eat a lot of fiber over the majority of our existence?  Dunno.  I kind of doubt it.  Seems to me we ate animal based food, concentrating on the fattiest bits we could get our hands on, and supplemented with plant based foods such as naturally low glycemic fruits and the occasional sprig of paleo parsley here and there when the body signaled it needed something in that parsley.  We didn’t hunt down the yucca plant and choose it over the bison liver.
>