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Book Summary: The Book of Humans: A Brief History of Culture, Sex, War and the Evolution of Us

Author: Adam Rutherford

Substory: Farming Ants

We excel at the use of tools to extend our reach beyond the limitations of our physical forms. These abilities are almost all taught rather than inherent, but are built upon biological foundations that allow these skills to develop. As we have seen of the animals that use technology, some skills are learnt, some are biologically encoded. But none comes close in sophistication. There are a couple of other characteristics worth examining that are truly part of our culture, and that may have apparent equivalents in other animals. Neither is a tool as such, but both are examples of humans extending their abilities by profoundly manipulating their environment. Both require tool use, and both are fundamentally important to humankind.

The first is agriculture. We have seen examples of organisms exploiting inanimate objects, and in the case of the sponging dolphins, one animal using a second to hunt for a third. There is another technique that we use to feed ourselves, in which we cultivate other organisms to harvest a food product. In humans, we call this farming. Agriculture changed humankind irreversibly and set the foundations for the current era. Over a short period of time, we went from being hunter-gatherers to being farmers who nurtured our own food and, in doing so, set in motion the wheels from which civilisation would emerge. Agriculture has been the dominant industry and technology for around 10,000 years. When it emerged, we see the evidence of new cereal crops being bred, rye in Mesopotamia, einkorn in the Levant. We see the domestication of wild boars and sheep in multiple locations around Europe and Asia. Within a period of 1,000 years or so after the retreat of the last Ice Age, the origins of farming spring up wherever there are humans. No longer would people need to track seasons or migrating animals to secure food. Permanent bases could be established, and crops stored for fallow years. Farming requires planning and foresight, to anticipate what will grow, how and when. This in itself drives technological innovation; pots for storage, colanders for processing food, ploughs and spades for tilling the earth. The overall effect is the centralisation of a valuable commodity, and that draws in more people. Economic disparity is created, and trade follows close behind. Because it was more stable, this changing lifestyle became dominant over foraging pursuits, and the practices were handed down and taught in and among families growing into communities.

Farming changed our bones and genes too. Our genomes reflect our changing diets more swiftly than many traits, and we can see the switch in agricultural lifestyles within our DNA, the classic example being in milk drinking. In Europe and in recent European emigrants, we drink milk throughout our lives. For most people on Earth today and historically, drinking milk past weaning is the source of all sorts of tummy troubles, as the enzyme required to break down a particular milk sugar called lactose works only during infancy. But at some point, around 7,000 years ago, probably in north-west Europe, people developed a mutation in the gene for that enzyme which meant that its function persisted throughout their lives. We had been husbanding dairy animals before this, and probably eating soft cheeses from their milks (processing milk into cheese removes the lactose sugar, so cheese can be consumed by anyone without effect), but not drinking their raw milk. After this mutation, combined with our farming practices, we had a new source of protein and fat, one for which we controlled the means of production. Its advantage to us is obvious, and it was selected not solely by nature but by the combination of our lives and the organisms we had crafted together. Now it is scored into our DNA.

I mentioned in a footnote on here that no organism has ever existed independently of others (while challenging the notion that a virus is not classified as being alive). That is certainly true, just as predators rely on prey, and ecosystem food webs are delicately balanced networks of interdependence. Agriculture is different. It is the industrial process of symbiotic cultivation, in the sense of being systematic worked labour in order to generate a grown product. The goats we milked 7,000 years ago were being shaped by domestication, and now they are what we made them.

Agriculture has been an essential cultural development that propelled us through history and into civilisation. We are not the only farmers though.

Leaf-cutter ants are famed for trotting along in television documentaries carrying colossal sections of foliage that they have snipped from a plant. However, the leaves are not the food they seek; what they want is a product made inside the cells of fungi from the family Lepiotaceae that they have crafted too, not directly, but by mutually beneficial evolution – the ants nurture the fungus, the fungus feeds the ants. Just like tilled soil, the leaves act as a substrate on which the fungus grows, which provides the ant colony’s essential food.

There are around 200 species of leaf-cutter ants that do this, and it’s been part of their existence for more than twenty million years. They are obligate fungal cultivars, meaning they fully depend on this activity, just as we do on farmed food. The dependence is mutual too: the fungus grows filaments called gongylidia, which are packed with nutritious carbohydrates and lipids, so that the ants can harvest them more easily to feed to the queens and larvae. Gongylidia don’t exist outside of fungal-ant agriculture.

There’s a further outrageous layer to this symbiosis. The leaf beds are prone to infection by another fungus, which the ants weed manually (actually, with their mandibles). But they also carry Pseudonocardia bacteria on their bodies and in specialised endocrine glands. These bacteria produce an antibiotic which attacks the fungal infections. This is an astonishing description of mutualism on many levels: an animal farming a fungus, using bacteria as a pesticide, each dependent on the others. Evolution is terribly clever, and we have a lot to learn from ants.