Mathematical model pushes back crop development by 10,000 years

Washington, September 20 : A new mathematical model has shown how plant agriculture actually began much earlier than first thought, pushing back crop development by 10,000 years.

A team led by Dr Robin Allaby from the University of Warwick in the UK developed the model.

Until recently, researchers believed 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, with the new study.

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, which was 18,000-15,000 years ago.

Other studies 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.

Using computer simulations, the new model that showed that over time, a cultivated population of crops 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.

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.

This mathematical model is 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.

According to Dr Robin Allaby, "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."

ANI