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3. Learning to live with exotic sexual practices: How plant breeding systems limit domestication: Vanilla, Beans, Figs, Hops, Avocados, Papayas, Carrots

Warren, J. CABI PDF

3

Learning to live with exotic sexual practices

Why are there so many species of flowering plants? The answer to this question is still hotly debated. Since the time of Darwin one of the leading theories has argued that plants have speciated by becoming genetically isolated from each other as a consequence of their individual relationships with unique species of co-evolved insects which pollinate their flowers. Insect pollination ensures that populations of plants can be genetically as separated from each other as if they were growing on different islands in the Galapagos. In this chapter we will discover that the bizarre pollination process found in many plant species has made them challenging to domesticate. This is because the necessary insect pollinators are not available widely enough or abundantly enough to allow the potential crop to be cultivated away from its home range or in sufficient quantity.

Plants so often do the most amazing things that we take them for granted. Some trees have the ability to live for thousands of years. It is entirely possible that olives are still being harvested from trees that Christ picked fruit from more than two thousand years ago. Similar things may also be true of plants that reproduce vegetatively. Although lacking the majestic grandeur of a tree, crops that regenerate from tubers may also technically live for many hundreds of years; but you would not recognize a geriatric potato if you saw one. Over evolutionary time, some species of plant may significantly increase the number of chromosomes they contain, through doubling, hybridization, or just the duplication or splitting of single chromosomes. In other plants, the amount of genetic material they

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7. Classic combinations and recurring themes: Plant families that have been repeatedly domesticated: Grains, Legumes, Pumpkins, Spinaches

Warren, J. CABI PDF

7

Classic combinations and recurring themes

We have seen that the chance of a wild plant being domesticated is rather rare. However, a small number of plant families have independently provided us with important crops on several occasions. This chapter tries to identify what makes these families so special. It appears that each of these families produces seeds or fruits that are easily stored, or leaves that can be harvested over a prolonged season. In addition to this, it turns out that their nutritional properties and agricultural requirements perfectly complement each other.

It is said that humans consume every part of the pig, except for its squeak. Although the hog may be a versatile creature, the ways in which we utilize plants are far more varied. In spite of the fact that we routinely eat so few of the plant species that are available to us, we have found a seemingly endless list of ingenious uses for every plant product on offer.

We dig up roots and underground storage organs, while fruits and seeds are devoured with relish. Plant sap is tapped to turn into rubber, or poured over pancakes as maple syrup or fermented to make birch sap wine. More viscous plant secretions give us varnish, glues and violin resin. Unopened flower buds provide us with the very different flavours of cloves and capers plus the rather less exotic tasting cauliflower. The stigmas and styles of crocus flowers are harvested to give us the spice saffron, and nectar is plundered from agave flowers to produce a range of desserts. The bark of trees provides us with items as diverse as cork, cinnamon and materials for building canoes. We use fibres from cotton and linen to make fabrics that are dyed using plant pigments. The fluffy fibres that

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5. The weird and wonderful: Herbs, spices and crops with exotic phytochemicals: Wasabi, Chillies, Saffron, Herbs, Willow, Tobacco, Cannabis, Durians

Warren, J. CABI PDF

5

The weird and wonderful

Although we gain most of our calories from a remarkably short list of species, our spice-racks, and medicinal and recreational drug cabinets in contrast are stuffed with the plants that are rich in an amazing diversity of chemicals. This chapter describes a range of the more unusual plants that we consume and tries to answer: why are we repeatedly drawn to minor crops that burn our lips and befuddle our brains?

It can be argued that all plants with the exception of grasses can be considered to be poisonous. The cells of plants contain a vast array of weird and wonderful chemicals. The biological function of many of these within these plants remains uncertain. However, once inside the human body these compounds may act as powerful drugs, potentially enhancing our health by mopping up cancer causing reagents, or they may help kill disease-causing microorganisms. Alternatively nature’s apothecary may impair our well-being. Plants may cause our demise by rapid poisoning, or slowly cause our death over decades. Other chemicals derived from plants cause allergies, intense burning sensations and befuddle our minds.

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6. Accidents of history: The role of chance events in domestication: Strawberries, Wheats, Bananas, Citrus, Rhubarb

Warren, J. CABI PDF

6

Accidents of history

Some crops seem just too good to be true. How on earth did our ancestors manage to develop bananas that don’t contain seeds? Or hybridize unrelated species to produce totally novel crops? This chapter covers a number of crops that have been created by our habit of growing related plants together and thus enabling them to unintentionally cross-pollinate each other. We also discover that although mutations are incredibly rare in nature, if you grow enough plants generation after generation, this random process can hit the jackpot and be responsible for the creation of new crops.

Humans have been domesticating crops for around 10,000 years. But not until 1900 and the rediscovery of Gregor Mendel’s experiments with breeding peas, did we have any real understanding of the laws of inheritance. In fact, it was as late as 1676 when plant anatomist, Nehemiah

Grew addressed the Royal Society that we started to appreciate that plants actually indulge in sex. In other words, for the vast majority of agricultural history we have not really had much of a clue about what we have been doing. The process of domestication has been one of simply identifying the most desirable or just unusual plants and propagating them.

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4. Storing up trouble: Plants with storage organs: Cassava, Yams, Potatoes, Taro, Akees, Onions

Warren, J. CABI PDF

4

Storing up trouble

Why do so few crops provide us with most of our calories? It is remarkable that we eat very few species of the plants that are available.

However, it is even more astonishing that we gain most of the energy we need to survive from a tiny sub-set of these species. This chapter explores this conundrum and finds that energy rich plants tend to contain toxins, and perhaps surprisingly, therefore, some of our most important crops have a propensity towards being poisonous.

In our modern world it is easy to be blissfully unaware of the most important challenge that species face. Although the solution to this problem may now seem trivial, for most of our history we have shared this challenge with plants and animals alike. In solving this dilemma for themselves, plants have frequently also provided us with a solution, while simultaneously creating a whole new set of difficulties for us to deal with.

The conundrum is ensuring that you have enough food to survive through lean seasons. The evolutionary struggle to eat and avoid being eaten has been highly influential in determining which plants we have domesticated, with different groups of crops providing us with sustenance and others helping protect this food from other hungry species competing to consume the same stores.

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