Let's unpack whether the question centers around nature vs. nurture or in plain terms the question would be, did we have enough time for human genes to take on the characteristics that are prevalent today in the obesity/T2D/Metabolic Syndrome epidemics that are rampant worldwide? They weren't common 50-60 years ago or before as we examine human history.

Paleo advocates have history supporting them in the sense that human agrarian systems and eating grown or raised foods have been around only for about 10,000 years, a minute time in humanoid evolution. Anyone familiar with human genetics understands that it takes many generations for genes to change and adapt (mutate). Based on environmental factors which include food, stress exposure, and toxin exposure among other things that can influence genetic change, it's reasonable to posit that these dietary changes started to contribute to health issues. To say 10,000 years is too short of a time for human genetic adaptation is an understatement. This is illustrated very well in the documentary "The Perfect Human Diet."

However, there is another dynamic that can cause changes among humans from generation to generation. That dynamic is called epigenetics where changes happen at the cellular level or "on or after" genes. It's been found that these changes at the cellular level including DNA methylation can in fact be passed on to subsequent generations. What's happening here is that while the human gene sequence takes an extremely long time to change, epigenetic characteristics at the cellular level have the influence of turning on or off genetic traits. These can be good or bad. Bruce Lipton's book, "The Biology of Belief" clearly explains epigenetics.

It goes to reason that since the human diet has changed very recently (10,000 years), it's very likely that the foods produced by humans and the accompanying eating lifestyles (eating timing, food availability and quantity) are very different than in Paleo times. As we've improved our food growing and manufacturing capabilities, we have also produced very harmful foods and eating habits. The consequences resulting in the epidemics mentioned earlier have been rapid and severe. That's why I believe it's very plausible that humans are better off when eating traditional whole foods and not eating all the time. Sugar? In the past, only during short windows of seasonally available foods was sweet stuff in the form of fructose available. Same for above-ground vegetables and fruits. Today, sugar is plentiful and we have super sugar concoctions as well. Sometimes when health issues arise so rapidly over a generation or two, one needs to ask, "What has changed?" Well, this is a pretty good summary of the potential root cause. Is it healthier to emulate Paleo eating? I'd be happy with an eating lifestyle similar to that in the first half of the 1900s (excluding refined grains and oils) before the engineering of different types of hardier, easier to grow wheat and grains, but a Paleo eating lifestyle certainly works very well for many and is a major improvement compared to today's standard diet.