1. Most Bananas in the World Are the Single Cavendish Variety
While bananas are sold cheaply in supermarkets around the world all year, most of them belong to a single variety called "Cavendish." [2] Even more surprising is that these Cavendish bananas do not produce seeds. Instead, they are propagated by cutting off part of the stem and planting it. [2] This means that Cavendish bananas worldwide are essentially a collection of clones with nearly identical genes. [2] When a group of living things consists of individuals that are genetically almost the same, that group carries a major weakness. In the past, this weakness caused an entire banana variety to suffer great damage and lose its place as the main choice.
2. Gros Michel Was the Main Banana Before Cavendish
Cavendish became the world’s main banana relatively recently. Before that, a different variety called "Gros Michel" was eaten worldwide. [1] However, in the 1950s, a disease called "Panama disease," caused by a fungus in the soil, struck Gros Michel plantations in Central America one after another. [1] Gros Michel was weak against this disease and suffered heavy damage. By the 1960s, exporters gave up on this variety and switched to Cavendish, which was considered tough at the time. [1] Thus, the bananas we eat today are mostly a "second generation" variety chosen to replace the former main one.
3. Cavendish Now Faces the Same Problem as Gros Michel
Ironically, Cavendish, chosen to replace Gros Michel, has the same weakness because it is also a clone grown from stem cuttings. Since the 2000s, a new type of Panama disease infecting Cavendish has been found. [2] This new Panama disease was first found in Colombia in 2019, in Peru in 2021, and in Venezuela in 2023. [3] Between 2018 and now, the number of countries and regions reporting damage from this disease has increased from 16 to 23. [3] Latin America is one of the world’s top banana-exporting regions. If this disease spreads, it could greatly affect farmers’ livelihoods and the global banana supply. [3] Cavendish holds the same weakness as Gros Michel. But why is being "genetically identical" such a big weakness?
4. Why Genetic Sameness Makes a Species Weak
The Ministry of the Environment in Japan explains that genetic differences within the same species determine "whether that species can adapt to changes in its surrounding environment." [5] If individuals within the same species have slightly different genes, some may happen to have strong traits against new diseases or environmental changes. This increases the chance that the species as a whole will survive. Conversely, if all individuals in a group have the same genes, one disease that exploits that weakness can wipe out the entire group at once.
History has already shown this lesson with a huge sacrifice. In 19th-century Europe, potatoes were grown by planting tubers from the previous year, not from seeds. As a result, cultivation was biased toward certain high-yield varieties, and genetic differences were almost non-existent. [4] In the Andes region of South America, where potatoes originated, there was a custom of mixing several potato varieties in one field, but this diversity was lost in Europe. [4] In 1845, a disease infecting potatoes spread in Europe. In Ireland, where there were few strong varieties, the damage was especially severe. It is said that 800,000 to 1,000,000 people died from disease and hunger during this "Potato Famine," and over 2,000,000 people moved out of the country. [4] The same weakness seen in bananas is recorded in human history on a much larger scale.
5. Biodiversity Has Three Levels, Not Just Species Count
The "genetic differences" we have looked at so far are just one of three levels that the term "biodiversity" refers to. The Convention on Biological Diversity, created in 1992, views biodiversity at three levels: "ecosystem diversity," "species diversity," and "genetic diversity." [5][6] "Species diversity" is the easiest to imagine; it refers to how many different kinds of living things are in a certain area. [5] "Ecosystem diversity" refers to the variety of ecosystems that exist depending on the environment, such as forests, rivers, tidal flats, and coral reefs. [5] "Genetic diversity" refers to the richness of differences among individuals within the same species, as we have seen. [5]
If we only look at the number of species in an area, we cannot see the danger held by groups like Cavendish bananas, which exist as a variety but have lost genetic diversity. Protecting biodiversity means protecting not just the number of species, but also the diversity within each species, and the diversity of ecosystems woven together by species, living things, and the environment.
6. Looking for Variety in Supermarket Fruits and Rice
Next time you go to a supermarket, look at the apple, mandarin orange, and rice sections. You should notice that even for the same fruit or crop, several varieties are lined up, such as "Fuji" and "Shinanogold" apples, or "Unshu mandarin" and "Dekopon." This is one form of the diversity remaining in cultivated plants that support our food. If you find several plants or animals of the same kind in a garden or park, compare their leaf shapes, flower colors, and sizes. You might notice that each one is slightly different. That visible difference is a clue to the genetic diversity that is thought to be the power protecting the kind.