Updated: Jun 21, 2018
If you've got 20 minutes to spare, listen to this radio interview with Marlene Zuk - an evolutionary biologist.
She takes a very common-sense and factual approach to 'Paleo' diets and lifestyle.
I believe that you should, in broad terms, eat as you've evolved to eat; so natural, unprocessed foods. However, be wary of claims made about how you should 'eat like a caveman' that have very little scientific and academic basis and simplify something that is far from simple. Some of the claims that I have come across are just stupid and seem to have come from someone who has watched the Flintstones and concluded that they're an human evolution expert!
The claim that you shouldn't consume dairy products is a good example of claim that isn't 'stupid', but is a gross generalisation. Many human populations have been able to digest lactose (the sugar in dairy products) for thousands of years - to be able to digest lactose beyond childhood would have been an evolutionary advantage for nomadic peoples. For many of us, there is nothing wrong with dairy. In my case, milkshake is my magic recovery drink!
Why eat strictly 'Paleo' (i.e. like some mysterious and generic pre-agricultural revolution human) when the science shows that humans have gone through major dietary adaptations in the last 10,000 years? If you can stomach dairy products and grains, go ahead and consume them in moderation.
I'm not an expert, but I would say that the biggest differences between our diet and the diet (broadly speaking) that we have evolved for is availability and quality. In the last century, food availability has increased and much of that food is poor quality, highly processed and hyper-palatable. So we are basically eating more crap food. If you can control quantity and quality (it's not always easy), you've got it sussed. Focus on these fundamentals and don't let gimmicky diets lead you astray!