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Duration:05:48
Uploaded:2019-10-14
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Not to deter you from eating your vegetables, but what if we told you that certain parts of your salads, like kale, broccoli, and cauliflower were all the same species?

Hosted by: Hank Green

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Sources:

https://pires.biology.missouri.edu/dogs-of-the-plant-world/
https://link.springer.com/article/10.1007/s10722-017-0516-2#Sec18
https://www.researchgate.net/publication/251322723_Origin_and_Domestication_of_Cole_Crops_Brassica_oleracea_L_Linguistic_and_Literary_Considerations_1
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lactuca-sativa
https://www.nature.com/articles/ncomms4930
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4279128/
https://www.nature.com/articles/ncomms13390
https://link.springer.com/chapter/10.1007/978-3-642-73520-2_11
https://www.jstor.org/stable/2482378?seq=1#page_scan_tab_contents
https://en.langenscheidt.com/german-english/kohlrabi
https://harvesting-history.com/the-kohlrabi/
https://www.sciencedirect.com/science/article/pii/S0960982295000728
https://www.nature.com/articles/s41438-018-0040-3
https://www.genetics.org/content/155/2/855
http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=26191
https://www.bolster.eu/spitskool-caraflex-f1-brassica-oleracea/p754
https://link.springer.com/article/10.1007/s10886-008-9429-z
https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.13015
https://www.sciencedirect.com/science/article/pii/S1674205218303836
[ intro ].

One of the most extraordinary things about dogs is how different they all are. Like, we took one wolfy species and made over 200 breeds from adorable wrinkly pugs to lanky, powerful greyhounds.

And we didn’t just do this kind of whole-body-tinkering with dogs. We’ve done it with plants, too. Just about all the fruits and veggies you can buy at the supermarket have been shaped by human breeding.

Most look totally different than their wild ancestors. But there’s one plant species that’s produced so many different varieties that it’s known to biologists as ‘the dog of the plant world’. You probably know it as kale.

And broccoli. And cabbage. And brussels sprouts.

T hat’s right, those are all the same species of plant. Foodie favorites like kale and cauliflower are just a couple of the cultivars, or human-modified and grown varieties, of Brassica oleracea. There are dozens more, from the logarithmic spiral of romanesco broccoli to the distinct, pointed shape of caraflex cabbage.

And you might think tons of variety is just what happens when humans selectively breed something for generations. But that’s not entirely true. After all, we’ve been growing and breeding lettuce for about the same amount of time, and yet, all lettuce varieties look pretty lettuce-y.

It turns out that B. oleracea is kind of a special plant. It was so transformable because it underwent some massive genomic event during its evolution. The story of why we have such a variety of this kind of plant starts millions of years ago.

Back then, an ancient Brassica ancestor did something quite remarkable— it tripled its genome. That massive genome was whittled back down to a more reasonable size by the time wild cabbage emerged as its own species about four million years ago. Still, it meant that wild cabbage ended up with a lot more genetic variation than your average garden plant.

You see, broccoli and kale and brussels sprouts don’t just look different. They’re very genetically distinct, too. And we’re not just talking little tweaks to genes.

In a 2016 paper, researchers sequenced the genomes of 9 different cultivars to construct the plant’s pangenome— the total genetic variation that exists in the species. And they found nearly 20% of the genes in that pangenome are only present in some varieties. So not only do cultivars have a lot of mutational differences, they also have whole genes that aren’t present in other members of their own species, even though they all came from the same wild cabbage.

That plant, as far as we can tell, originated in the coastal areas of southern and western Europe. We don’t know exactly when our species first grew and domesticated it, but genetic evidence suggests it may have been around 2000 B. C.

E. The earliest written records come from ancient Greece, and they suggest the first cultivars were leafy— veggies like kale and collard greens. And the Greeks weren’t the only ancient people who tinkered with wild cabbage.

Scientists are pretty sure that the plant was domesticated many times in several locations. Some of these domesticated varieties found their way back into the wild, became feral, and then were re-domesticated, adding even more to the species’ genetic diversity. And all that genetic diversity eventually allowed people to magnify different structural parts of the plant.

The variety we now call cabbage, for example, seems to have arisen sometime before the tenth century when people bred a kale-like plant to have larger buds on the tips of its stems. Brussels sprouts are also enlarged buds— the buds that grow all around the length of the stem. And scientists aren’t quite sure when the cultivar first emerged, but it was definitely being grown in Belgium by the end of the 18th century.

Then there’s kohlrabi, which literally means cabbage turnip in German— presumably referring to its bulb-like enlargement at the base of the stem. It’s not clear when it first came about, either, but historical literature suggests it was grown throughout Europe by the 1500s. Then there’s broccoli and cauliflower.

Both get their unique florets—the yummy parts we eat— from mutations to flowering genes. In broccoli, those mutations lead to a lot of flower buds packed tightly together. Cauliflower has a lot of tightly packed flowering structures, too, but most of them never actually flower.

Instead, the white, pre-bud flower tissue replicates itself as it grows, leading to the familiar, curd-like head. Since both have modified flowers, it’s thought that one came from the other, but it’s still not totally clear which came first. As of 2018, genetic research seemed to be leaning toward team broccoli.

In fact, scientists are still trying to piece together how we got all of these amazingly different versions of Brassica oleracea and in what order. Trouble is, the same genomic shuffling events which gave this species so much genetic diversity also make it challenging to figure out a precise timeline for these cultivars and their relationships to each other. Researchers are eager to figure out as much of that as they can, because it will also help them better understand how the different varieties tolerate different environments, resist different diseases, and produce different nutrients.

You see, by better understanding these nutritious, delicious, and fascinating dogs of the plant world, scientists just might figure out how to make our favorite crops more hardy, sustainable, and nutritious. If you think these flexible plants are incredible,. I bet you’ll like our episode on eight plants that have mastered the art of deceit.

And we’ve got so much more mind-blowing science to tell you about! We put out a new video here on SciShow every day. And if you click that subscribe button and ring the notification bell, you won’t miss a single one. [ outro ].