A friend is reading a new book called Go Wild: Free Your Body and Mind from the Afflictions of Civilisation. It has inspired him to go a bit "paleo", diet-wise. It says, for instance, that humans were not meant to eat grains. I don't want to dis a book that could help people become more mentally and physically healthy, but the notion that human beings were somehow designed (by God? by Mother Nature?) to only ever eat or do certain things, and that these things were dictated in some heyday hundreds of thousands of years ago, comes up a lot, and smells a little like baloney to me.

Raw foodists claim we were not meant to eat anything cooked. Some vegetarian campaign groups are adamant the "natural human diet", as eaten by our ancestors, is herbivorous. Paleo dieters say we were designed to eat lots of meat and veg, and agree with the gluten-free clan that eating grains was never part of the master plan for human nutrition. Are any of them right?

Evolution lessons

Guess what? There was never any master plan for human nutrition. Evolutionary biologist Marlene Zuk, in her recent book, Paleofantasy, challenges misconceptions about evolution. We may be almost genetically identical to how we were 40-50,000 years ago, but it's not that simple. We are also, genetically speaking, 98% chimp and 35% daffodil. "How you use that DNA" must be taken into account, says Zuk. Evolution happens in fits and starts and we have changed plenty, she adds. Some populations developed the ability to digest lactose – the dairy sugar – after weaning (which no mammal had done before), about 5-7,500 years ago. This was a result of cattle farming, and the gene became common in, for example, northern Europe. Furthermore, "there are genes that control the production of amylase, an enzyme that breaks down starch, and populations with a long history of eating grains, such as in Japan, have more copies of amylase genes than people from other parts of the world, so it's clear there have been lots of genetic changes, over a relatively short period of time".

She also thinks it's unhelpful to view evolution as perfectionist, so statements such as "we were perfectly adapted to …" are guff. As the Nobel-prize-winning scientist François Jacob once said: "Evolution is a tinkerer, not an engineer." It takes what it has and jerry rigs it together so that it works at the time, says Zuk, "and it just has to be good enough".

The paleolithic diet

This eating programme permits meat, fruit and veg, fish, nuts and seeds, and eschews coffee, booze, starches (spuds are out), grains, legumes, "processed" food and dairy. Colorado State University scientist and paleo diet exponent Loren Cordain says that westerners now get 70% of their diet from four sources: refined grains, refined sugars, dairy products and refined vegetable oils. It is clear that the modern diet isn't working out for us, but why the dramatic U-turn to paleolithic? Because, the theory goes, when that period finally came to a close 10,000 years ago, we started farming and that's when our diets started to go pear-shaped. And Cordain holds to the notion that, genetically speaking, "we are basically stone agers living in the fast lane", and therefore our optimum diet is paleo.

However, anthropological pedants have pointed out that paleolithic hunter-gatherers' diets were many and varied according to where they wandered, and part of the secret of our success is that we have always been omnivores. Besides, says Zuk, "increasingly people are starting to think that early humans ate more grains than we originally assumed". She cites a 2010 study that found evidence in Europe of starch grains having been ground into flour and mixed with water 30,000 years ago. Furthermore, you can only really do the diet if you are wealthy. As Daniel Lieberman, Harvard professor of evolutionary biology, has it: "A) we can't feed the whole world on grass-fed beef, sorry, and b) there are still a lot of question marks around eating as much meat as you possibly can."

Raw food

"It is a return to the way we were designed to eat. Nature doesn't make mistakes; it gives each species everything it needs in order to thrive. If we were meant to eat cooked food, we would have been born with built-in ovens!" This is from the raw-food website fresh-network.com. Can it be true, I ask the eminent NHS consultant gastroenterologist David Sanders. The way to sort this out, he suggests, is to ask: "Do you develop a disease as a result of eating cooked food? The answer is no." Plus, cooking has the benefit of rendering meat safer to eat, and toxic foods edible, such as potatoes and kidney beans.

However, it is true that our genus, Homo, has been unable to cook food for most of its existence so far. "If you picture the two million years of Homo's existence on a 24-hour clock," says Cordain, "it wasn't until between 20 and 40 minutes to midnight that we could cook. So our genome was conditioned by vastly different foods." The raw foodists have a point then? "It's not a practical point, because we live in a completely different world," he says, "so we need to take the best of their world, utilise it, and leave the worst behind – which is eating raw meat."

Vegetarianism

We have always had small canine teeth and lacked strong claws, reason those who think humans are natural herbivores. But scientists can tell whether our ancestors ate meat by analysing their bones and, says Cordain, "in the bones we dig up from Africa from two million years ago, and from Neanderthals in Europe, and Homo erectus in Asia, there's not a single exception. They were all omnivores and ate a lot of meat. Zuk also mentions one anthropological theory: that before he were hunters, we scavenged other animals' prey.

Gluten free

Sanders, who is chair of the Coeliac UK Health Advisory Committee, says he is inclined to agree with the statement that our bodies aren't designed to eat gluten, or at least quite so much of it, which is why coeliac's disease, gluten allergy and intolerance are all on the rise. "A slice of bread has about 2.5g of gluten so you think that's what you've had, but then it's in your Mars bar, X, Y and Z – they've all got gluten in them." He doesn't follow a gluten-free diet, however, because he doesn't have any symptoms associated with it. These sorts of decisions are a personal calculation and come down to common sense.

Would you subscribe to a way of eating because it is billed as evolutionarily correct?