Until recently researchers say the story of the origin of agriculture was one of a relatively sudden appearance of plant cultivation in the Near East around 10,000 years ago spreading quickly into Europe and dovetailing conveniently with ideas about how quickly language and population genes spread from the Near East to Europe. Initially, genetics appeared to support this idea but now cracks are beginning to appear in the evidence underpinning that model
Now a team led by Dr Robin Allaby from the University of Warwick have developed a new mathematical model that shows how plant agriculture actually began much earlier than first thought, well before the Younger Dryas (the last “big freeze” with glacial conditions in the higher latitudes of the Northern Hemisphere). It also shows that useful gene types could have actually taken thousands of years to become stable.
Up till now researchers believed in a rapid establishment of efficient agriculture which came about as artificial selection was easily able to dominate natural plant selection, and, crucially, as a consequence they thought most crops came from a single location and single domestication event.
However recent archaeological evidence has already begun to undermine this model pushing back the date of the first appearance of plant agriculture. The best example of this being the archaeological site Ohalo II in Syria where more than 90,000 plant fragments from 23,000 years ago show that wild cereals were being gathered over 10,000 years earlier than previously thought, and before the last glacial maximum (18,000-15,000 years ago).
The field of Archaeobotany is also producing further evidence to undermine the quick development model. The tough rachis mutant is caused by a single recessive allele (one gene on a pair or group of genes) , and this mutant is easily identifiable in the archaeological specimens as a jagged scar on the chaff of the plant noting an abscission (shedding of a body part) as opposed to the smooth abscission scar associated with the wild type brittle rachis.
Simply counting the proportion of chaff types in a sample gives a direct measure of frequency of the two different gene types in this plant. That study has shown that the tough rachis mutant appeared some 9,250 years ago and had not reached fixation over 3,000 years later even after the spread of agriculture into Europe was well underway. Studies like these have shown that the rise of the domestication syndrome was a slow process and that plant traits appeared in slow sequence, not together over a short period of time.
Genome wide surveys of crops such as einkorn and barley that in the past that have suggested a single origin from a narrow geographical range, supporting the rapid establishment view, have long been in conflict with other gene studies. The most notable conflict is in the case of barley for which there is a large body of evidence that suggests more than one common ancestor was used in its development.
These challenges to the fast model of agricultural development need a new model to explain how and why the development was so slow and demonstrate why artificial selection of just one plant type does not have the expected quick result. This computer model has now been provided by Dr Robin Allaby and his team at the University of Warwick, the Institute of Archaeology, University College London, and Manchester Interdisciplinary Biocentre has outlined the new mathematical model in a paper published in Proceedings of the National Academy of Sciences USA 2008 and in a summary article in the Biologist (2008 55:94-99).
Their paper entitled The genetic expectations of a protracted model for the origins of domesticated crops used computer simulations that showed that over time a cultivated population will become monophyletic (settle into one stable species) at a rate proportional to its population size as compared various gene variations in the wild populations. They found this rate of change matched closely the 3000 years it took the tough rachis mutant to become established.Ironically, this process is actually accelerated if there is more than one
This mathematical model also more supportive of a longer complex origin of plants through cross breeding of a number of attempts at domestication rather than a single plant type being selectively bred and from a single useful mutation that is selectively grown quickly out paces the benefits natural selection
Dr Robin Allaby says:
“This picture of protracted development of crops has major implications for the understanding of the biology of the domestication process and these strike chords with other areas of evolutionary biology.”
“This lengthy development should favour the close linkage of domestication syndrome trait genes which may become much more important because linked genes will not be broken up by gene flow – and this makes trait selection and retention easier. Interestingly, as more crop genomes become mapped, the close linkage of two or more domestication syndrome genes has been reported on several occasions.”
“This process has similarities to the evolution of ‘supergenes’ in which many genes cluster around a single locus to contribute to one overall purpose.”
“We now need to move this research area to a new level. Domestication was a complex process and can now be viewed more legitimately as the paragon of evolutionary process that Darwin originally recognized. There are many interacting factors involved that we know about operating on a wide range of levels from the gene to the farmer and climate – the challenge is to integrate them into a single story.”
Peter Dunn | alfa
Climate change, population growth may lead to open ocean aquaculture
05.10.2017 | Oregon State University
New machine evaluates soybean at harvest for quality
04.10.2017 | University of Illinois College of Agricultural, Consumer and Environmental Sciences
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research