Why humanity cultivates only a few plant species

For example, three companies (Apple, Samsung, Xiaomi) control two thirds of the global smartphone market, and four companies (CFM International, Pratt & Whitney, General Electric Aviation and Rolls-Royce) produce more than 80 percent of all jet engines installed on commercial aircraft. Domesticated plants are no exception to this common rule. Botanists have classified nearly 400,000 species of vascular plants, around twelve thousand of which are herbaceous plants that produce small but nutritious seeds; yet only a small fraction of these have been selected for agriculture. Just twenty species account for 75 percent of the crops cultivated annually, with two domesticated herbaceous plants — rice and wheat — providing 35 percent of the world's food energy.

Domestication is a process of targeted selection and gradual alteration of wild species in order to obtain plants or animals with characteristics better suited to satisfying human needs. It is a process that has been studied (starting from the descriptions Charles Darwin gave of the changes observed in cultivated plants) using a combination of different scientific methods, among which modern genetics and genomics are among the most productive. The final result of domestication is modified plants and animals whose survival and spread depend on the care provided by humans.

Almost all major crops were first domesticated between 13,000 and 5,000 years ago in at least seven different regions of the planet, beginning with wheat, sorghum, millet, rice, potatoes, chickpeas and peanuts (more than 9,000 years ago), followed by barley, maize, common beans, cassava and sugar cane (more than 6,000 years ago), and later soybeans, rapeseed, cowpeas and quinoa (more than 3,000 years ago).

Archaeologists, geneticists and biologists who have studied domestication have identified several noteworthy recurring characteristics, and the oldest domesticated plants show a greater number of these traits compared to more recently adopted varieties. The reason is that while some of these traits may have been acquired within a few decades, others required a millennium to become established. In wheat, rice, barley and soybeans, the most important change was the stronger retention of the grains (that is, a sturdier ear whose kernels do not spontaneously fall to the ground once ripe), and wheat, one of the two main staple cereal crops, developed significantly larger kernels, while maize and domesticated sunflowers reduced the number of leaves. But the most common traits of domestication are differences in taste (normally less bitter and sweeter than wild varieties) and the larger size of edible parts (larger seeds, fruits or tubers).

The fruits of domesticated plants display the most evident differences compared to their ancestors, whether it is the wild kiwi (small, with tougher skin and a sour taste, compared with the larger, softer and sweeter fruits of cultivated varieties) or any species of drupe: apricots, cherries, peaches and plums are much smaller, harder and less sweet in nature. Wild bananas are full of small, hard seeds, but in cultivated varieties we can barely notice them as dark specks at the center of the fruit. And seedless oranges (navel, Valencia and satsuma) make up a large share of the global citrus market. The most widespread consequence of all these alterations is reduced genetic diversity.

Among domesticated plants there are very few "cone-bearing" trees, namely conifers. Their resin-rich bark and pointed needles are not suitable for eating (although the needles can be used for an infusion), and the exposed seeds that remain on the upper part of the female cones detach as easily as they are difficult to collect. The price at which pine nuts — the seeds of the pine tree, an essential ingredient for making authentic pesto alla genovese — are sold in supermarkets is a sign of the effort required to harvest them.

About two thousand species (equal to half a percent of all vascular plants) have been fully or partially domesticated, and only two hundred of these have achieved significant regional or global distribution.