Microevolution in Cabbage

Brassica oleracea

Maybe you've heard this Latin epithet before, maybe you haven't. You've definitely eaten it though, unless you're the kind of person who avoids vegetables. A non-exhaustive list of cultivated crops in this species: broccoli, cauliflower, cabbage, bok choy, kale, brussel sprouts, collard greens, kohlrabi, and more. This particular species of plant in the Mustard family, Brassicaceae, originally lives on the rocky, limestone outcrops of Great Britain and France. It has since been proliferated and domesticated into God-knows how many forms of yummy veggies by cultures across the globe. Although all these different cultivars, like dog breeds, aren't different species per se, the microevolution this plant has undergone in the past couple thousand years under humanity's guiding hand is undeniable, staggering, and awe-inspiring... to me at least.

To the left, you'll see a nice summation of what was selected upon to form the various crop cultivars now existing of this versatile little plant's genome. I find this to be so representative of Darwin's prediction of microevolution because of how dramatic the consequences of selection for these specific traits were upon this single species of Brassica. I think it's fair to consider artificial selection by humans as tangential to selection that could have occurred from environmental factors. For example, if B. oleracea's environment had become particularly nutrient or water deprived, who's to say there wouldn't have been a selection on bigger stems for advantageous resource storage that would have resulted in a form similar to kohlrabi? It of course is speculation with regards to whether that would have happened or not but it's definitely a feasible possibility and not hard to imagine. Another example, perhaps a genetic group of individuals with a bit more tolerance for shade slowly colonize shadier areas of the environment and in the process larger leaves get selected for to catch more sunlight for photosynthesize under a theoretical tree-cover. Boom, kale. 

Interestingly enough, according to Quiros and Farnham, 2010, alongside human intervention in this genome, genetic "introgression" occurred from diverse wild forms of the plant which probably added spice to the breeding regiments of cultivated plants (which were grown in close proximity to these wild B. oleracea.) This introgression is deemed as potentially equally important in the microevolution of these cultivars as the human hand was. That is to say, I think this shows that there really was a solid "natural" potential for this microevolution (and eventually speciation) to occur without our assistance. This goes for many crop domestications, and animal domestications too, but artificial selection, in regards to microevolution, seems to me as the human hand bringing forth potential that nature had already instilled in organism lines. These microevolutionary changes could have happened (and did in the case of B. oleracea, as mentioned above) as a result of natural selection rather than artificial selection, simply based on the fact that we were able to make the change happen. Cabbage, everybody.

References:

Quiros C.F., Farnham M.W. (2011) The Genetics of Brassica oleracea. In: Schmidt R., Bancroft I. (eds) Genetics and Genomics of the Brassicaceae. Plant Genetics and Genomics: Crops and Models, vol 9. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-7118-0_9

https://botanistinthekitchen.blog/2012/11/05/the-extraordinary-diversity-of-brassica-oleracea/