Humans have domesticated over 1000 plant, animal, fungal and bacterial species, some just for their good looks

What is domestication? Michael D. Purugganan. Trends in Ecology & Evolution, May 6 2022. https://doi.org/10.1016/j.tree.2022.04.006

Highlights

. The study of domestication has seen enormous strides in recent years, but the concept of domestication has been unclear.

. The core nature of domestication is as the coevolution between domesticator and domesticate.

. Evolutionary and ecological studies with both human-associated domestication and non-human domesticators can help us understand the nature of this phenomenon.

Abstract: The nature of domestication is often misunderstood. Most definitions of the process are anthropocentric and center on human intentionality, which minimizes the role of unconscious selection and also excludes non-human domesticators. An overarching, biologically grounded definition of domestication is discussed, which emphasizes its core nature as a coevolutionary process that arises from a specialized mutualism, in which one species controls the fitness of another in order to gain resources and/or services. This inclusive definition encompasses both human-associated domestication of crop plants and livestock as well as other non-human domesticators, such as insects. It also calls into question the idea that humans are themselves domesticated, given that evolution of human traits did not arise through the control of fitness by another species.

Keywords: mutualismcoevolutionhuman domesticationinsect farmingperi-domesticatesweedscommensalsagricultural originsornamental species

Are humans domesticated?

The question of whether humans are domesticated has a long history and Darwin considered this question briefly in Descent of Man [65]. The idea of human domestication, especially the concept of ‘self-domestication’, has gained momentum in recent years based on the assertion of similarities in traits between humans and domesticate mammals, including evolution of smaller body sizes, shortening of the face and a reduction in tooth size, reduced sexual dimorphism, and a reduction in cranial capacity [66., 67., 68., 69.]. More importantly, these morphological changes are accompanied by a decrease in reactive aggression and increase in docility and prosociality [68,69]. Finally, the concept of self-domestication has been extended to include bonobos [70].

Invoking the term ‘self-domestication’ as applied to humans (and bonobos) is problematic. Darwin dismissed the idea of human domestication, as he understood that humans had not been subject to the control of its fitness, which is one of the critical hallmarks of domestication [65]. Moreover, the idea of self-domestication is untenable, since domestication as a biological concept is rooted in a mutualistic interaction with another species. Finally, defining domestication based on shared phenotypic similarities is also fraught with problems, given that such similarities could also arise outside the context of domestication [71,72].

While there are some trait similarities between H. sapiens and domesticate animals, in humans these do not appear to have evolved as a direct result of the mutualistic interaction with domesticate species. Such phenotypic similarities may arise from parallel/convergent evolution [71,72], possibly associated with secondary effects of the domestication process (for example, increased population density or sedentism) [68,69] but arguably do not directly spring from the human/crop, human/livestock, and human/pet mutualisms. Those who have remarked on these similarities need to explore other mechanisms to explain these evolutionary convergences.

Concluding remarks

Here, I have attempted to provide a broad but rigorous biologically centered definition of this unique phenomenon. In this overarching biological conception, domestication has the following critical elements. It is: (i) an evolutionary process, (ii) arising from mutualistic ecological interaction, (iii) involves constructing an environment where there is control of the fitness of one species by another, (iv) occurs so that the domesticator can garner resources and/or services from the domesticate, (v) leads to fitness benefits that accrue to both partners, and (vi) is agnostic to the interacting species. The pace of domestication is governed by the strength of the selection exerted by the domesticator (and the environment it provides) and the genetic and ecological characteristics of the target domesticate.

This definition has the advantage that it is grounded in evolutionary and ecological concepts, first recognized by Darwin [52,53] and later on championed by others [7,10,14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25.]. Like any definition, it struggles for both inclusivity and exclusion and there may well be cases that present some ambiguity. Indeed, domestication has understandably come to mean many other things and undoubtedly its varied usage will continue. It is expected, however, that the biologically oriented view presented here can provide a more precise conceptualization of domestication, help sharpen discussion of cases as they arise, and focus attention on major issues surrounding fundamental aspects of this phenomenon (see Outstanding questions). With a comparative, evolutionary, and ecological framework [1,2,10,16,19,26,27,73], there is an opportunity to understand the nature of this coevolution and the dynamics of this unique mutualism.

Outstanding questions

What are the ecological and evolutionary pathways that lead to domestication?

To what extent do the partner species rely on the mutualism for their survival and reproduction?

Does every individual domesticated organism have to impart a fitness benefit to the domesticator?

How do we determine whether a species is domesticated?

In human-associated domestication and subsequent diversification, what are the relative roles of conscious versus unconscious selection?

How do we understand domestication and selection for aesthetic traits?