While it is quite reasonable to assume that humans have been manipulating and cultivating crops for food for a long time, researchers at University College London (UCL) in the United Kingdom have recently been able to give us an idea of just how long we’ve been at this.
Dorian Fuller and Charlene Murphy of UCL have recently conducted a study which indicates that the domestication of the legume horsegram (Macrotyloma uniflorum), may have occurred from as early as 1200 BC.
Horsegram is a bean commonly eaten in Northern India.
How Did They Do It?
Results indicate that the domestication of horsegram seeds took place at least as early as the 2nd millennium BC. It seems that the coating thickness became fixed around the early AD period.
The team from UCL made use of the Diamond Light Source Synchrotron facility in order to measure the thinning of seed coatings in archaeological seed samples.
A synchrotron is a source of high energy X-rays. The X-rays are produced by steering an electron around a storage ring using bending magnets. This radiation can then be “tapped off” at end-stations called beamlines, where the X-rays can be used to study the structural properties of various materials. Visit Diamond’s website to learn more about how a synchrotron works.
Seed coating thickness can tell researchers a lot about if a plant is domesticated or wild. Thinner seed coatings indicate domestication, since this thinner coating allows for faster germination when a seed is watered.
High-resolution X-ray Computed Tomography
Germination marks the beginning of the growth of a plant from a seed.
The team made use of a technique called high-resolution X-ray computed tomography (HRXCT) at the I13 beamline of the Diamond Light Source to image and subsequently measure seed coatings of a sample set of seeds.
Seed Coating Thickness
By using a beamline at the Diamond Light Source, the research team was able to image their samples without damaging them. It should be noted that there are other methods which allow for the imaging of seeds without damaging them. However, these techniques can only image a single spot of the seed.
This means that researchers are unable to get an idea of what the seed looks like as a whole easily. HRXCT, on the other hand, allows for the entire seed to be imaged.
In total, the team looked at 12 seeds. They found that they were able to group them as wild or domesticated based on the thickness of their coatings. They classified wild seeds as having coatings thicker than 17 micrometres, and domesticated seeds as having coatings between 10 and 15 micrometres.
A micrometre is 100 000 000 smaller than a centimetre.
Their results indicate that the domestication of horsegram seeds took place at least as early as the 2nd millennium BC. It seems that the coating thickness became fixed around the early AD period.
What Does This Research Mean
This research gives us important insights into the history of crop domestication. This was also the first time that the HRXCT technique was used to image archaeological seeds. This opens up the opportunity to look at the history of other types of seeds, essentially broadening our agricultural knowledge.