Above: Image by Rick Harris
Humans are a genetically diverse species, and sexual reproduction leads to many variations within any human population. For example, a trait such as hair colour can vary greatly. But genetic diversity is not just about physical appearance. Humans are also very different when it comes to metabolism, resistance to disease, and inherited genetic disorders.
Did you know? Cavendish bananas have a high dopamine content. Dopamine is a “feel good” chemical released by your brain.It is an entirely different story with Cavendish bananas, the generic yellow species you see in every supermarket. Unlike us, the Cavendish banana is asexual. Once a banana plant has produced its bunch, it is chopped down so a new plant can grow from its own shoots. This new plant is genetically the same as its parent. In fact, every single Cavendish in the world is genetically the same. The banana that you sliced into your cereal is exactly the same as the banana that someone in South Africa had for a snack.
The ancestors of the modern supermarket banana actually had large seeds throughout their flesh. But a mutation occurred in one of these ancestral bananas, causing it to become seedless. Since then, these Cavendish bananas have been selectively bred for seedlessness, which has now become the norm. The little black bits we see in bananas today are just the remnants of the seeds that were once present in virtually all bananas.
The Cavendish banana's lack of genetic diversity means they will all taste more or less the same. But it also means that when a deadly disease strikes, there are no genetic variations that might help some members of the species survive.
Did you know? Every once in awhile, a mutation in the form of a small, hard seed can be found in a Cavendish banana!In fact, before the 1950s, the most popular species of banana was the Gros Michel. Like the Cavendish, all Gros Michels were genetically identical. Unfortunately, they were afflicted by a fungal infection called Panama disease, named after its place of origin. The Tropical Race 1 strain of the disease caused a type of Fusarium wilt, which yellowed and wilted the leaves before killing the rest of the plant. Because all Gros Michels were genetically identical, they were all equally helpless when faced with this soil-borne disease.
With no resistance, total banana wipeout was imminent. Luckily, the Cavendish came to the rescue. Although inferior in taste, it had one advantage: resistance to the Tropical Race 1. Almost overnight, it became the new banana of choice.
Yet it looks as if the Cavendish may ultimately suffer the same fate as the Gros Michel. A new strain of Panama disease, called Tropical Race 4, has already wiped out entire plantations in Asia and Africa. Thankfully, the disease has yet to reach Central America, the main exporter of Cavendish bananas, But when it does, the Cavendish banana will likely be wiped out.
Waiting to take its place is the Goldfinger banana, a shorter species that is more time-consuming to grow. A Goldfinger might just end up in your morning cereal in the near future!
Can Science Save the Banana? (Julio Cordova, Steve Kirsky and Dan Koeppel, Scientific American) We Have No Bananas (Mike Peed, The New Yorker) Yes, We Will Have No Bananas (Dan Koeppel, The New York Times) The Sterile Banana (Fred Pearce, Conservation Magazine)
Kanazawa K, Sakakibara H. 2000. High Content of Dopamine, a Strong Antioxidant, in Cavendish Banana. Journal of Agricultual Food Chemistry. 48(3):844-848. Ploetz, RC. 2005. Panama Disease: An Old Nemesis Rears its Ugly Head Part 2: The Cavendish Era and Beyond. APSnet Features. http://www.apsnet.org/publications/apsnetfeatures/Pages/PanamaDiseasePart2.aspx Visser J, Gordon T, Fourie G, Viljoen A. 2010. Characterisation of South African Isolates of Fusarium Oxysporium F.SP. From Cavendish Bananas. South African Journal of Science. 106(3-4):1-6. http://www.sajs.co.za/sites/default/files/publications/pdf/154-1238-1-PB.pdf