RowanasRowanas however makes an excellent point about running, in the comments. Since arms do extend beyond the hips, running can be performed with hands alone, albeit with a smaller stride - check his comment for the full idea.
This contrasts with the solutions that real-world humans of this era found, one of which was stalking mammoth. Having discovered that, inferior solutions or those harder to come up with would have been overlooked or just not used. While humans without legs would not be able to run behind mammoths throwing spears with their arms effectively, they can still stalk prey covertly in groups, trap it or use other techniques that for us are inefficient.
This would limit their food supply, assuming their approaches are inferior, which would limit the sizes of their populations and hence the growth rate of their species. But I don't think that it can be said to be definitively impossible to survive the hunter & gatherer phase, or to say that not having legs is a death sentence for a species of otherwise human capability.
Addendum by tepples
This contrasts with the solutions that real-world humans of this era found, one of which was stalking mammoth. Having discovered that, inferior solutions or those harder to come up with would have been overlooked or just not used. While humans without legs would not be able to run behind mammoths throwing spears with their arms effectively, they can still stalk prey covertly in groups, trap it or use other techniques that for us are inefficient.
This would limit their food supply, assuming their approaches are inferior, which would limit the sizes of their populations and hence the growth rate of their species. But I don't think that it can be said to be definitively impossible to survive the hunter & gatherer phase, or to say that not having legs is a death sentence for a species of otherwise human capability.
