There's of course something going unmentioned in all this. Despite a wildly different rationale and back-story, the practical everyday dietary reality of doing the Paleo diet is very similar to the Atkins diet. The weight-loss, then, should not be surprising. And many of the "criticisms and concerns" levied against Atkins ought to be considered relative to the Paleo diet as well. There are unfortunately no conclusive long-term studies on either diet, and the long-term effects of low-carb diets are not truly understood. All the positive evidence for Paleo is first-person and anecdotal, but we're left to wonder how something that feels so healthy, and make so much historical sense, could be wrong.
There are plenty of unresolved criticisms of Paleo that need to be examined. First and foremost is that while Paleolithic-era humans may have been fit and trim, their average life expectancy was in the neighborhood of 35 years. The standard response to this is that average life expectancy fluctuated throughout history, and after the advent of farming was sometimes even lower than 35. It's only in recent modern history, with the advent of nutrition, that life expectancy has soared. The contemporary Paleo diet, we are told, is the best of both worlds.
But the jump in life expectancy occurred not over the last decade of two, in the age of food science. It happened over about a hundred years. It was the result of advances in agriculture that increased the world-wide supply of food, eliminating malnutrition. People have survived into their 90s and beyond on very simple and traditional diets of pasta, bread, vegetables, and small portions of meat. It seems that lumping all "processed foods" into one group is a fundamental mistake. There are ancient processed foods like bread and pasta, and there are relatively new processed foods like potato chips and hot dogs. The latter, along with fast food, sugary sodas, and the like (sometimes referred to as the American diet) are to blame for the current obesity epidemic and many of our society's food-related health problems.
More to the point, the contemporary approach to Paleolithic eating ignores what must have been the overriding reality of actual Paleolithic people: the scarcity, inconsistency, and lack of variety of their diet. It's absurd to think you're eating like Paleo-man if you're having filet mignon one day, lobster the next, and duck the next, while also consuming eggs and a supermarket's worth of vegetables, nuts, and berries. Paleolithic diets surely varied by region, but mostly they probably consisted of a few staple foods, with periods of abundance and not infrequent periods of scarcity.
There is no question that we should eat more fresh and unprocessed foods. But if there's a charge to be levied against carbohydrate-heavy foods like bread and pasta, it's that they make it easy for us to eat way too much, not that they're bad in and of themselves. (Sugar, however, may be another story altogether.) So the Paleo diet's dictum to eat as fresh as possible is shared universally with all modern sane eating guidelines. Its rationale for avoiding traditional carb-heavy foods falls apart under scrutiny. And it's success at producing weight loss and health may have more to do with portion control than anything else. But perhaps the deepest cut was a "US News comparison" of 20 diets (including Atkins, veganism, the Mediterranean diet, and Jenny Craig) that ranked Paleo dead last on criteria like nutrition, ease of following, weight loss, and safety.