Research out of the USA is questioning our knowledge of how the earliest crop plants were ‘tamed’ and domesticated
The story of how ancient wolves came to claim a place near the campfire as humanity’s best friend is a familiar tale (even if scientists are still working out some of the specifics).
In order to be domesticated, a wild animal must be tamable – capable of living in close proximity to people without exhibiting dangerous aggression or debilitating fear.
Taming was the necessary first step in animal domestication, and it is widely known that some animals are easier to tame than others.
But did humans also favour certain wild plants for domestication because they were more easily ‘tamed’?
Research from Washington University in St Louis calls for a reappraisal of the process of plant domestication, based on almost a decade of observations and experiments.
The behaviour of erect knotweed, a buckwheat relative, has WashU paleoethnobotanists completely reassessing our understanding of plant domestication.
Natalie Mueller, assistant professor of archaeology in Arts & Sciences at Washington University, said: “We have no equivalent term for tameness in plants, but plants are capable of responding to people. They have a developmental capacity to be tamed.”
Her work with early indigenous North American crops shows that some wild plants respond quickly to clearing, fertilising, weeding or thinning.
Plants that respond in ways that make cultivation easier or more productive could be considered more easily tamed than those that cannot.
She added: “If plants responded rapidly in ways that were beneficial to early cultivators – for example by producing higher yields, larger seeds, seeds that were easier to sprout, or a second crop in a single growing season – this would have encouraged humans to continue investing in the co-evolutionary relationship.”
This capacity to express different traits and characteristics in response to the environment is called plasticity, and not all species are equally plastic.
Mueller advised: “Some plants respond quickly and obviously to cultivation and care. I think ancient people would have noticed that they could double their yields just by thinning out dense stands of plants.
“This is one of the simplest and most common gardening techniques, but it has many important effects on the development of plants.”
Mueller’s study focuses on work with a plant called erect knotweed, a member of the buckwheat family that was domesticated by indigenous farmers in eastern North America.
The domesticated sub-species is now extinct; humans don’t eat it anymore. But Mueller and others have previously uncovered caches of seeds stored in caves, charred plant remnants in ancient hearths, and even the seeds of erect knotweed in human faeces, clear evidence that this species was once consumed as a staple food.
Mueller, who studies lost crops, has spent years growing erect knotweed and other crop progenitors in experimental gardens, including at Washington University’s environmental field station, Tyson Research Center.
She hasn’t always been successful with growing the plants she collects in the wild. In that way, Mueller can relate to the early farmers who similarly experimented with plants to discover their potential. Her efforts have often been stymied by seed dormancy, a common feature among wild plants.
With erect knotweed, Mueller experienced a breakthrough of sorts. Based on four seasons of observations, Mueller determined that growing wild plants in the low-density conditions typical of a cultivated garden (i.e. spaced out and weeded) triggers plants to produce seeds that germinate more easily.
This makes the harvests easier to plant successfully the next time around, eliminating a key barrier to further selection.
She said: “Our results show that erect knotweed grown in low-density agroecosystems spontaneously ‘act domesticated’ in a single growing season, before any selection has occurred.”
Think of it as the plant equivalent to that first wolf who, though still a wild animal, sat down with its human friend around the fire. This is a behavioural shift, rather than an evolutionary one, but it allows new evolutionary pathways to open up.
Process of domestication
Mueller believes there is a bias in domestication studies toward viewing this changeability, or plasticity, as noise that is getting in the way of attempts to explain evolutionary change. Instead, this paper argues that we need to understand the development and behaviour of wild crop relatives in order to explain the evolutionary process of domestication.
She said: “Because we lack the practical experience with crop progenitors that ancient people had, these effects of the environment on plant development have gone mostly unnoticed and understudied.”
Her findings could have applications for developing new food crops; there is no reason why we have to be limited to the plants that our ancestors domesticated thousands of years ago.
Some researchers have been calling for de novo domestication – selecting wild plants with desirable characteristics and intentionally domesticating them. It may make sense to start looking to wild plants that are easily tamed as potential crops that could be developed for the future, Mueller said.
She concluded: “You can’t explain plant domestication if you only consider the behaviours of humans, because domestication is the result of reciprocal relationships between multiple species that are all capable of responding to each other.”
The research is published in PLOS ONE.
Image 1: Erect knotweed
Image 2: Research from Washington University in St Louis calls for a reappraisal of the process of plant domestication, based on almost a decade of observations and experiments. The behaviour of erect knotweed, a buckwheat relative pictured here, has WashU paleoethnobotanists completely reassessing our understanding of plant domestication.
Both images © Natalie Mueller/ Washington University in St Louis.