Human evolution, was it all about starch?

salivary amylase gene copies and hydroxycarboxylic acid receptors

It’s still a bit of a mystery why the so-called Neolithic agricultural revolution was such a success. Why is it that grain culture spread so rapidly in so many places around the world? The various impacts on our ancestor’s health were, in general, pretty negative. People became shorter, they started to have repetitive strain injuries and a lot of dental problems, amongst other things. Despite this, grain-based agriculture spread far and wide and today these grains; wheat, rice, maize, oats, barley, etc are staple, dominant foods.

Could it all have to do with salivary amylase gene copies (AMY1)? This is the burning question. The more one has of these genes the better one digests starch, the amylase breaks it down to glucose. It seems that we already had, on average, 4 to 8 AMY1 copies per diploid cell 45,000 years ago. This was back when we were all hunter-gatherers and suggests that starchy foods were part of our diets. Our cousins, the Neanderthals and Denisovans, had multiple AMY1 copies too which would seem to indicate that getting our heads around some good starchy tubors, french fries and suchlike predates the split between us and our cousins. That was around 800,000 years ago so it’s been going on for a long time. Our oral microbiomes changed too, at least 100,000 years ago, shifting and adjusting as we ate more starch.

Then along comes the current inter-glacial period which saw atmospheric CO2 levels rise. Some plants more than others exploited the higher levels by developing bigger leaves and bigger seeds. Our ancestors noticed this and started to cultivate them and this was all helped along by our AMY1 gene copies. We started eating more starchy foods and our genes responded by producing more and more AMY1 copies. Europeans increased the number of AMY1 copies from around four to at least seven over the last 12,000 years. The period corresponds to the development of agriculture. This would seem to indicate that those people with higher numbers of AMY1 copies had better reproductive success, they had more kids who survived to reproduce and so on.

So hunter-gatherers had a better, more diverse diet and were healthier. Yet they were quick to adopt the new farming stuff that settlers from what is now central Turkey turned up with. One can’t help imagining a farmer-type encouraging a hunter-gatherer to stick his bison steak and a few wild onions in between two slices of bread. Perhaps the future of humanity at that time was decided by people making Kebabs, who can say? Whatever it was, and bear in mind that our ancestors were at least as keen of mind as we are and probably much more observant, they decided to put down their suitcases and become sedentary farmers. They probably wouldn’t have noticed the negative health impacts or perhaps didn’t associate them with the new dietary regime. What they did see was an easier way to survive and thrive, one to which they were already genetically adapted.

We were also, thanks to our third that burns like indigestion, adapted to eating fermented foods. Most species have two HCA protein receptors on the surface of their, we and the other Great Apes have three. When they are busy fermenting, lactic acid bacteria produce a metabolite called D-phenyllactic acid. This metabolite bonds to the 3rd receptor and sends a message to our immune systems that what we are eating is OK. This enables us to eat fallen fruits that have started to ferment. So the HCA receptors and the AMY1 copies led us along the road to Friday nights in the bar followed by a Kebab.

Whatever it was that encouraged our ancestors to change their diets we subsequently managed to do what we do so often. Take a good thing and make it bad. It looks like we were giving our starchy leftovers to our pigs and dogs as they also started to have increasing numbers of AMY1 copies on their diploid cells. Today we farm immense areas to feed livestock with starchy foods, cutting down virgin forests to increase these areas. The areas put to grain culture for direct human culture are equally vast. Nowadays we have diets that are dramatically less diverse than those of our hunter-gatherer ancestors and this is not good for our health. In economic theory bread is sort of weird, for normal goods as the price goes up demand goes down. This isn’t the case with bread, the price goes up yet demand stays more or less steady. Eventually, the price hits a certain level and people hit the streets and start protesting and overturning governments.

After some periods of relatively stable climatic conditions, we are now heading into unknown and rising waters. Our ancestors faced something similar although not so rapid, they wouldn’t have known what was causing the changes either, but we do. Temperatures increased, icepacks melted and sea levels rose. Tsunamis became more common and people had to move back and away from the disappearing coasts. Vegetation changed and spread northwards accompanied by the animals who could survive the still cold conditions. Over time our ancestors changed their way of life to become settled farmers. We are going to have to do something similar, perhaps in a few centuries’ time anthropologists will talk about the Neoplastic agricultural revolution. If so what would their research show? A radical and rapid change away from extensive synthetic chemical plow-based farming and an upsurge in all different types of agroforestry. When they analyze our dental plaque they will see that we moved away from grain dominance to eating more nuts and fruits. Perhaps they will be amazed at how we quickly diversified our diets and how our health improved. They’ll probably still find some traces of Friday night booze and kebabs though, if you’re going to have a Neoplastic agricultural revolution it’s got to be fun.

It may be that future archeologists will see traces of a rapid phase of de-urbanisation as people left sinking cities prone to frequent flooding and spread back into the countryside. Future people who research historical economies will write papers about how we moved to stable state, zero growth systems. Their peers studying historical demographics will win Nobel prizes for their research on how, as the global population declined, it came to hit a stable level. Working with the economists they will give conferences about stable population levels, stable state economies, and how they made everything better for all Humanity.

That would be nice.