Carrots!

I was extremely pleased when I learned that my daughter's homework was to assemble a set of facts about the carrot. How little I ever learned about food and farming at school – despite the fact that food and farming keeps us fed, that farmers have a greater impact on our landscape than anyone else, and that food and farming is the largest single sector of the UK economy. One of my intellectual heroes, Thoreau, would have approved of a little girl of age seven taking a break from spelling and mental arithmetic to study the humble carrot.

I naturally found myself telling my daughter a story that tried to explain each of the things that make carrots distinctive, in terms of the ecology and evolution of the wild carrot from which they were bred. Going over Wikipedia, we could see how each apparently isolated fact – for example, that carrots can be stored for months in the fridge – makes complete sense, once you understand what the wild carrot evolved to do. Similar stories could be told of any one of our important food plants. More importantly, the ecological understanding embodied in those stories could help us ensure a sustainable global supply in coming decades and centuries.

But back to the carrot. In contrast to many of the crops grown in the UK, the carrot, or at least its relative the wild carrot, is native to the UK, so I'm already on its side. The wild carrot has evolved to take advantage of 'disturbances' – patches of bare ground that are naturally opened up by anything from a large tree coming down in a forest, to a landslip, to a flood, to a river or stream shifting its course, to an animal scraping up the soil. When such a disturbance happens, it causes a temporary break in the dominance of long-lived (perennial) plants, and opens up an opportunity for short-lived, fast-growing plants that can complete their life cycle, from seed-to-seed, before the perennials close in again. Annual plants complete the cycle in just one year. But the wild carrot is slightly slower, taking two. This makes it a 'biennial'. The strategy of a biennial is to get well established in the first year, just like an annual. But later in the year, when an annual would be diverting all of its productivity to producing seeds, a biennial diverts its productivity to an energy store, most commonly a swollen root. The above-ground part of the plant dies off completely at the end of the first growing season. But the root survives. In year two, a biennial uses the energy in the store to quickly build up a new plant above ground, in order to get a very rapid leg up on the competition. This enables it to capture most of the resources during that second year (goodbye annuals), and then produce a truly massive output of seeds – some of which are lucky enough to land in the next disturbed patch so the process can begin again.

So we can immediately explain some things about carrots. Why does the carrot make a swollen root at all? It's a store of energy to get a leg up on the competition in the following spring. Why do carrots store so well in the fridge? Because the root has evolved to survive in the cold winter soil for months on end. Everybody knows that you can create a new carrot plant just from a little carrot top. Why? Because in nature, this very thing happens at the beginning of the second growing season.

But the list doesn't end there. An unprotected store of energy, available in the middle of winter, is highly attractive to all kinds of enemies, from insects to fungi, mammals and bacteria. Therefore, the carrot has evolved to fill the root with various chemicals that make it much less attractive, even toxic, to those enemies. These chemicals give carrots their characteristic colour and flavour. Interestingly the wild carrot, and old varieties of the domesticated carrot, are smaller, darker, and stronger tasting than modern varieties. As with most crops, in modern times we have bred out most of the carrot's natural defenses, and with them most of the flavour, in order to increase the yield. As a result, we now need to apply artificial chemicals to keep down those same enemies.

I also find it interesting that, according to Wikipedia, carrots were first domesticated for their leaves and seeds, rather than their roots. I assume that the carrot was picked for this purpose because, if you could find some of the roots, you could easily plant them and get a guaranteed good harvest above ground. As any vegetable gardener can tell you, the larger the seed, the easier the plant is to grow, and growing plants from swollen roots, as we do with potatoes, is the easiest of all. This may also explain why we didn't eat the roots. That would require growing plants from seed, which is hard. Carrot seeds are small (a greater number of smaller seeds means a greater chance of the getting to the next patch). But if you grow it from a root the carrot plant considers that it is now in growing season two, and diverts its productivity to leaves and seeds. I also wonder whether the roots of those very old varieties were so well chemically protected that they were simply unpalatable? This would be an additional reason to grow them for their seeds rather than their roots.

Now, the nutritional status of the Earth's ten billion or more inhabitants over coming decades is not going to hinge on the carrot. But the story of the carrot is a reminder that all of our crops are descended from plants that evolved and survived in the wild for aeons before we humans ever cultivated them. The next green revolution, which unlike the last one is going to be about increasing yields without increasing energy and material inputs, will depend on understanding this ecological history, and how to build upon it, for example through genetic modification, new farm technology, and new holistic methods to managing the farm ecosystem. Of course, the second green revolution will mostly be driven by people who are children now. Good job they’re already learning about carrots.

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