Tag: Evolution

Agriculture and Artificial Selection: Domestication through the Lens of Cabbages

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Did you know that kale, cauliflower, Brussels sprouts, and many other cabbages are all part of the same species, Brassica oleracea? If that interests you, join us for a deep dive on domestication and artificial selection!

Domestication and agricultural selection are a huge part of our daily life, from our fur, feather, scale, or leaf babies to food and clothing. Continue reading if you want to learn more about how they came to be that way!

A bit of history

We first domesticated plants (most likely non-intentionally at first) around 13,000-11,000 years ago in the Fertile Crescent. Some of the first crops include wheat, barley, flax, and legumes. These plants started as wild, and over long periods of time, artificial selection changed them into the crops we know today.

However, domestication is not synonymous with agriculture; agriculture is dependent on domesticated species, but domestication does not automatically lead to agriculture.

Animals were not all domesticated in the same place or at the same time. The current scientific consensus points to multiple points of origin: for example, dogs are thought to have been domesticated around 12,000 to 10,000 BCE in modern-day Iraq. Other archeological finds let us think that they might have been domesticated more than once: dated from 10,000 to 7,000 BCE in England, Palestine, Japan, and the US. Some scientists even proposed dates as early as 33,000 years ago (Freedman and Wayne 2017).

A map of the domestication places of the main domesticated animals and crops. Among the most notable: the difference between Old World and New World farm animals and plants, cats in Egypt, overlaps between the Fertile Crescent, Europe, and Asia.
Probable domestication places of the main domesticated animals and crops. Figure from Michael Park’s Introducing Anthropology, 4th ed. 2008, p.237 (Note, this is an older map, and the scientific consensus has changed since it was drawn.)

Most farm animals (sheep, goats, pigs, and cattle) are thought to have been domesticated around 6,000 BCE in Mesopotamia.

Domestication of everything and anything?
Not all species, animal, plant, or other, are suitable for domestication. The wanted characteristics are: hardiness, social behavior, herd dynamics, utility, easy reproduction, and manageable husbandry. The last two criteria in particular let us to select which individuals are permitted to breed. Thus allowing us to select for traits we would like to see in the offspring, which is the guiding principle behind artificial selection (Driscoll et al. 2009).

Domestication is a gradual, multigenerational process in which humans selectively breed animals for specific functions and benefits. It is also characterized by a mutual (but not equal) advantage in the form of protection and care extended to the selected individuals, as well as increased numbers and range (although in plants it can interfere with seed dispersal).

Domestication is a lineage-level process that impacts the genetic material of the population, whereas taming only brings behavioral modifications at an individual level.

Did you know? Humans are not the only domesticators; 3 separate insect groups each domesticated fungi, some as far back as 30 million years ago!

And what about cabbages?

B. oleracea probably originated from the Eastern Mediterranean region, and the earliest physical evidence of domestication points to around 3,000 years ago. Modern crop cultivars mostly come from Europe or Asia.

Suitable habitat for Brassica cretica, probable ancestor of modern domesticated B. oleracea varieties. This habitat is mostly found in the coastal and island regions of Greece and Cyprus.
Suitable habitat for Brassica cretica, probable ancestor of modern domesticated B. oleracea varieties during the late Holocene (4,200 years ago to present). Figure 3C from Mabry et al. 2021.

From the original wild Brassica oleracea, multiple different traits have been selected for by humans (passive): enlargement of leaves for kale, proliferation of lateral buds for Brussels sprouts, enlarged flowers and arrested development for broccoli, etc.

Early artificial selection targeted whole traits. But nowadays, it works mostly at the gene level, using marker-assisted selection and genomic selection. Both methods allow for quicker selection of desirable individuals, thus accelerating the creation of new varieties.

Mini-Game! “Associate crops to their signature trait!” (Answers at the bottom of the article)

License: Created in https://BioRender.com

Brussels sprouts are a good example of modern artificial selection. Until quite recently, they were bitter and less sought after. But in the 1990s, a Dutch scientist, Hans van Doorn, selectively cross-bred modern high-yielding plants with historic, less bitter-tasting varieties. These new Brussels sprouts were less bitter and sweeter, but retained the high-yield abilities of the modern varieties.

We humans started domesticating plant and animal species some 10 to 15,000 years ago. This ever-ongoing process changed its methods over time, from only trait selection to genetics, but the principle stays the same as for our ancestors!

Mini-game answer (click me!)

A = 3
B = 4
C = 2
D = 1

Lexicon

  • Cultivar: a cultivated plant variety or strain that retains artificially selected traits when cultivated and propagated.
  • Variety (agriculture): a population of plants that may occur naturally; they also present specific and stable traits.

Sources

Rabbithole starter