Limits and constraints to crop domestication 

Markus G. Stetter, 2020

 

The domestication of plants and animals was one of the most significant changes in human history. A managed cultivation of crops allowed a sedentary lifestyle and the division of work, which freed capacities to develop modern societies.

The change from a wild plant to a crop required substantial morphological and physiological adaptation. Crops with similar uses display similar trait changes, which are summarized in the domestication syndrome (Hammer, 1984). For grain crops, loss of seed shattering, increased seed size, and loss of seed dormancy are major domestication traits (Fig. 1). Crops that combine most domestication traits and consequently are well adapted to agroecological environments can be considered fully domesticated, while those that only display a few crop traits may be considered as incompletely domesticated. Although hundreds of grain crops have been cultivated by humans for millennia, most plants show only few of the domestication traits rather than the full syndrome (Meyer et al., 2012). Consequently, only a small fraction of the over 2000 crops that we know today are fully domesticated. Even crops that were of high importance for early cultures display only a minor fraction of the domestication syndrome. Studying the signals of incomplete crop domestication in minor crops could reveal the limits and constraints of crop selection and unlock the potential of novel crops for sustainable food production. 

Here, I review the evidence of potential genetic limits and constraints that altered the path of crop domestication. I present potential genetic features that might have favored the rapid full domestication of certain plant species and hindered the complete domestication of others. My examples and conclusions are mostly based on annual grain crops because their domestication syndrome is well defined and overlapping. Yet, most of the concepts also hold true for tuber, root, fruit, and vegetable crops, although more domestication traits are based on human preferences (i.e., flavor and color) for these crops.

 

Paths to full domestication. The genetic makeup of the ancestors of major crops allowed them to progress straight on the path to domestication. Other plant species had to take detours on the path and are consequently less domesticated today. The detours taken differ among crops, and constraints are not independent. The order and number of detours are specific to each crop.

 

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