As I wrote previously, you don't have to believe in evolution. It's not the belief or confidence in it that helps you out, anyway. What makes the difference is acting as though it were true, along with hypothesizing or educated guessing what was probably true for us, over eons, then simulating and modeling a life to capture those advantages for yourself.
It's worked for me and plenty of others, has generally been a blast and natural, and most importantly, affords us a life way going forward that can remain a blast, and natural. This is the essential beauty of it. I think diets would be a lot more effective for a lot more people if they could honestly look forward to living that way for the rest of their lives. Can you imagine living on the Dean Ornish chubby-face diet, for life?
But, in order to really capture the advantages and become your own authority, you do need to at least understand what it is that the theory of evolution postulates. And here's something along those lines. Carl Zimmer takes a look at the 20-year (and running) experiment by biologist Richard Lenski. The notion of evolution, most simply, says that every now and then a genetic mutation produces a benefit rather than a detriment, and that over huge swaths of time, these add up. Detrimental mutations (most of them are) just run their course, but beneficial ones give an organism an edge, either in competition for existing food sources, competition for mates, or — and probably most powerful of all — ushering in entirely new food sources. The latter is the subject of the article.
More but: you can actually see this work, provided you can use organisms that reproduce fast enough. For Lenski, that involved using E. coli bacteria, with which he's been able to run through 44,000 generations. Counting human generations as 30 years in length, this is roughly equivalent to 1.3 million years of human evolution.
Lenski started off with a single microbe. It divided a few times into identical clones, from which Lenski started 12 colonies. He kept each of these 12 lines in its own flask. Each day he and his colleagues provided the bacteria with a little glucose, which was gobbled up by the afternoon. The next morning, the scientists took a small sample from each flask and put it in a new one with fresh glucose. And on and on and on, for 20 years and running.
Based on what scientists already knew about evolution, Lenski expected that the bacteria would experience natural selection in their new environment. In each generation, some of the microbes would mutate. Most of the mutations would be harmful, killing the bacteria or making them grow more slowly. Others would be beneficial allowing them to breed faster in their new environment. They would gradually dominate the population, only to be replaced when a new mutation arose to produce an even fitter sort of microbe.
Lenski used a simple but elegant method to find out if this would happen. He froze some of the original bacteria in each line, and then froze bacteria every 500 generations. Whenever he was so inclined, he could go back into this fossil record and thaw out some bacteria, bringing them back to life. By putting the newest bacteria in his lines in a flask along with their ancestors, for example, he could compare how well the bacteria had adapted to the environment he had created.
Today, those bacteria breed 75% faster than their ancestors. That's not all.
Out of the blue, their bacteria had abandoned Lenski's glucose-only diet and had evolved a new way to eat.
At about 31,000 generations, some E. coli evolved to eat citrate in addition to glucose, giving them a huge edge. You can read the article for all the details, because that's not really my principal point.
…in generation 31,500, they made up 0.5% of the population. Their population rose to 19% in the next 1000 generations, but then they nearly vanished at generation 33,000. But in the next 120 generations or so, the citrate-eaters went berserk, coming to dominate the population.
This rise and fall and rise suggests that the evolution of citrate-eating was not a one-mutation affair. The first mutation (or mutations) allowed the bacteria to eat citrate, but they were outcompeted by some glucose-eating mutants that still had the upper hand. Only after they mutated further did their citrate-eating become a recipe for success.
You may think this a stretch, but that sounds a lot to me like the advent of human agriculture, only with a twist. Now, human technology is not "evolution," but a consciously guided by-product of it. It's not natural selection.
Looking around, tens of millions of people are on a path to destruction. If we were still evolving naturally, i.e., with no means of controlling or altering our environment except to move to someplace else, then we might expect to either adapt on large scale to eating grains, or they would so debilitate us that grain eaters would eventually go extinct, as did two lines of hominid vegetarians. Instead — and thankfully so I should add — we strive to overcome the issue in a deliberate, medical way. That link right above is both frightening and amazing. We're clearly now engineering our own evolution, for better or worse.
But you don't need to risk all that.