Plant and animal domestication has altered the evolutionary history of humans as well as a considerable number of extant species. Despite our understanding of the patterns of domestication improving, the evolutionary and agricultural effects of such processes exemplify the extent to which human activity is modifying whole environments and the species they encompass.
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Agricultural history and origins of domestication
A domesticated species is defined as a species bred in captivity under human control, who influence its food supply and reproduction, thus being a distinct process from taming wild-born animals.
Domestication played a considerable influence in human history, as it is hypothesized that domesticating plant was the reason humans transitioned from nomadic to agricultural practices. Although only 14 large mammals have been domesticated throughout agricultural history, it is estimated that over 2,000 plant species have been modified through human cultivation.
Worldwide, domesticated livestock contributes to 60% of all mammal biomass on earth, with humans contributing 36%, and wild species only representing 4%. Such skewed biomass generates many ecological and environmental issues, which were discussed in a 2002 review by Jared Diamond in the Nature journal.
The review elaborates on the complex history of domestication, focusing on key questions such as the reason underlying the limited number of domesticated species. For instance, of the 200,000 wild species of higher plants, approximately 100 were domesticated successfully. Moreover, the author also discusses the rarity of domesticated large mammals, using examples such as the zebra to illustrate the difficulty in breeding certain species.
The benefits and repercussions of domestication for humans
For human populations, domestication is fundamental to establishing long-term sources of food and resources, which was a turning point in early human evolution. Current evolutionary theory suggests domestication emerged in several geographic areas throughout ancient history. Combined with the range of species now considered domesticated, this indicates that there are multiple advantages to domesticate animals and plants.
For instance, domesticated plants and animals not only act as a stable source of resources but can also contribute towards other elements of human life such as protection and warfare, but also social status and attractiveness.
However, early patterns of domestication in both plants and animals suggest that agricultural producers breed species primarily that can sustain higher pest and environmental stress.
Nevertheless, the domestication of plants and animals also generated negative repercussions for human populations. For example, domestication is well recognized to have been the most significant cause of animal-borne diseases.
Domestication allowed for denser human populations to aggregate due to the stability of resources, providing an ideal environment for diseases to transmit and to evolve faster in comparison to diseases originating from wild species. Instances of such consequences occurred with the emergence of measles and tuberculosis, originating from cattle, as well as influenza, which originated from pigs and ducks.
The domestication of plants and animals, therefore, contributed to human evolution by providing a greater number of resources but also by generating many consequences that are still relevant in contemporary societies.
The direct effects of domestication for species
Domestication has influenced many aspects of organism life history including the behavior, genetics, demographics, and geographic range of many species.
The alteration of traits is particularly well documented in modern livestock when comparing them to their wild ancestors. Chickens were selected to be larger, wild-caught cattle to be smaller, and sheep to lose their kemp but avoid shedding their wool so humans can use it. In aquatic species, trout have been selected to have smaller brain sizes to avoid losing valuable energy that could be used for growth.
The human desirability of traits of value, therefore, directed the strategy and thus lineages involved in the domestication of many species.
This is particularly true in dogs, which were the first domesticated animal and display some of the most extensive range of morphological traits across breeds despite being a single species. Dogs were initially used for protection and have evolved alongside humans, resulting in many complex interactions such as the understanding of human facial expressions and vocal patterns.
However, despite being the first domesticated species, recent evidence revealed additional unforeseen complexity to patterns of domestication. The study from December 2020 published in the Journal of Ethnobiology showed that dogs evolved stronger bonds towards female human individuals. This indicates that dog-human coevolution was disproportionately influenced by the relationship with women, suggesting further complexity within patterns of domestication that are yet to be revealed.
The indirect effects of domestication in species
Genetically, domestication can often lead to many changes in evolutionary lineages including the demise of species through population bottlenecks caused by a reduction in the genetic diversity of lineages.
Domestication can also affect non-target organisms. Because the phenotype of domesticated organisms differs from their wild counterparts, organisms that interact with domesticated species experience altered selective pressures to adapt to these novel phenotypes.
This occurred in Colias butterflies, which shifted host types to accommodate for the newly cultivated legumes used in agricultural production. This shift resulted in genetically distinct populations that now depend on different host types with separate evolutionary trajectories.
Another occurrence was studied by Frank Messina in 2004, who documented the host shift of the wild seed beetle Callosobruchus maculatu. Results showed that the competitive environment between larvae after shifting to the domesticated cowpea plant affected the phenotype and ultimately the survival of this species.
Moreover, a 2018 study showed that human impacts affected the demography and genetic diversity of plant species even before their use for cultivation. Using the whole-genome resequencing data of extant plant species to determine the history of plant domestication, researchers suggested that humans affected species primarily through ecological and reproductive modifications.
In plants, the accelerated domestication of species through molecular techniques such as CRISPR will expand the plant types currently used in domestication. For animals, the growing diversity and abundance of species used as livestock or the pet trade will further contribute to the effects of domestication. Ultimately, domestication is a process illustrating the influence and impacts of human activity across lineages of both domesticated and non-domesticated species.
- Chambers, J., Quinlan, M. B., Evans, A., & Quinlan, R. J. (2020). Dog-Human Coevolution: Cross-Cultural Analysis of Multiple Hypotheses. Journal of Ethnobiology, 40(4), 1. doi: 0.2993/0278-0771-40.4.414
- Diamond, J. (2002). Evolution, consequences, and future of plant and animal domestication. Nature, 418(6898), 700–707. doi:10.1038/nature01019
- Gaut, B. S., Seymour, D. K., Liu, Q., & Zhou, Y. (2018). Demography and its effects on genomic variation in crop domestication. Nature Plants, 4(8), 512–520. doi:10.1038/s41477-018-0210-1
- Messina, F. J. (2004). Predictable modification of body size and competitive ability following a host shift by as seed beetle. Evolution, 58(12), 2788–2797. doi:10.1111/j.0014-3820.2004.tb01630.x
- Turcotte, M. M., Araki, H., Karp, D. S., Poveda, K., & Whitehead, S. R. (2017). The eco-evolutionary impacts of domestication and agricultural practices on wild species. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1712), 20160033. doi:10.1098/rstb.2016.0033