Therein lies the inherent flaw with the Paleo Diet - it's near impossible to tell what our ancestors ate that far back, or even if it's even relevant.
Depending on who you choose to believe, we were either all out there hunting mammoths and wooly rhinos and living off what was basically BBQ food, or we were eating lots of fruits and grains. Then adding to this, there is a school of though that suggests genetic variance happens very slowly and we are physically the same as we were 100,000 years ago.
What we do know is that in the period roughly between 10,000BC and 6,000BC, we definitely started cultivating the staples - wheat, barley, rice etc.
We also know that populations can diverge very quickly and that advantageous mutations also happen quickly. The common example to cite here is alcohol. Historically, if you were European, your water intake would come from an alcoholic drink as the alcohol removed toxins from the water. If you were east Asian, your water intake would come boiled water, which also obviously has the toxins removed.
As a result, it is well documented that a substantial chunk of the East Asian population do not process alcohol in the same way that Europeans do, leading to a phenomena called Asian Flush (or more properly, alcohol flush reaction). The obvious conclusion is European populations had a selection pressure which meant those who could process booze well would survive. Asian populations didn't have the same selection pressure and so the gene sequence required is less widespread.
Don't worry, all this is leading somewhere....
...similarly, once people started eating grains (whenever that was), almost certainly those who had the gene to produce amylase were the most successful in surviving. The fact we produce amylase should be evidence enough that people have eaten carbs for millennia and even if the 'original' humans didn't, that's irrelevant. The point is, we can. As a side note, the fact that if you put starch in your mouth it near instantly turns into sugar should be something to think about for people with diabetes.
None of this, however, changes the basic biological fact. There is absolutely nothing in a carbohydrate that cannot be obtained from another food source. Carbohydrates are literally just energy and nothing else. Yes, certain carbohydrate sources will have vitamins in them but interestingly, the bulk carbs (bread, rice, potatoes) offer next to no nutritional value beyond energy - certainly when you compare them to say, broccoli or beans.
Therefore provided a person's diet contains all the vitamins they need and the energy they need, I would imagine they could safely not eat carbohydrate and suffer no ill effects as a result. How practical this is, is another matter.
If we want to get really philosophical about this, carbs are why we have civilisation. Carbs are an energy dense food source, which means you don't have to go out hunting all the time to find a rabbit to eat. If you've got a secure food supply that gives you all the energy you need, you have more freedom to do other things. And that's when people start doing things like putting a big rock on top of some round logs and giving it a push, and finding out what happens when you squidge some clay together and leave it in the fire for a bit.
So in that roundabout way, eat however many carbs works for you. For some it's none. For some it's plenty. You don't need them, but you don't necessarily need to cut them out either.
