In the old city of Rigilusburgh, as the legend says, the finest warriors were trained day and night to protect the city. Among them, and as always, there were cowardly and brave soldiers. The brave dreamt of future battles where they would fight with honour, while the coward were quite happy to stay around, showing off and pretending they were eager to go to war. The brave were calm by nature and did not need anyone to tell them what to do, but some insecure cowards came around, and the courage of the brave was such, and the energy of their speech was such, that the coward became brave just by listening to them. However, the brave lived a solitary tough life, and sometimes that was too much to bear. Over-weighed by worries and inexistent battle, they became cowards themselves, and came back to find refuge in the crowd.
One day, because of the prosperity of the city, the soldiers were forced to expand and colonize new territories. They all started together, the brave and the coward, but at the very front of the army, where there were not that many warriors, the brave found themselves alone, some of them becoming cowards, the others finding it difficult to convince others. This allowed the coward to gain advantage. However, close to the front there were still some brave soldiers who tried to call for the ones who were behind them, and made them speed up a bit, because they still could see the new territory, free of human activity, free of cowards.
Regrettably, at some point, the cowards took so much advantage, that the foremost brave soldier could not see the new territory any more, it was all full of cowards. That was a sad day. There was no point in trying to call the others to find a land he could not see. At that point, he decided to slow down and regroup with the other brave soldiers in order not to disappear completely. From that moment on, the brave advanced slowly inside the mass of cowards, trying to convince as many of them as possible, and trying not to become cowards themselves.
Suddenly, the danger came, the enemy gates were reached, and then all the cowards that had thought too much of themselves died easily at their enemies’ hands. They called for the braves, they begged for them to come, but they were far behind, and the Rigilsburgh soldiers died, and the city knew nothing about them.
It was only after some time that the brave slowly caught up and finally found the enemy. All their cowardly friends were piled up at the gates while the enemies laughed from above. That offence ought to be avenged, and it would be indeed. They were brave soldiers from Rigilsburgh after all. They grouped, they fought, they took their bows and arrows, their shields and swords, and the heads of the enemies were rolling down the walls before the night came. The brave soldiers took the wall and saw what laid in front of them. A land infested with enemies, a land for the braves to conquer, and endless battle to fight.
As the braves defeated the enemy, a few cowards joined them after the wall, but most of the territory was still dangerous, and the bodies at the wall put most of them off, so it was only a few of them that were not coward enough to join the brave, and waited there for the moment to become brave themselves, to live in this land of endless battle.
The Science behind the Story
This story, and part of the following explanation, are included in my PhD thesis, published by the University of Edinburgh in 2013. Only a few minor corrections have been added.
I worked on a project that involved the propagation of bacteria that were either susceptible to an antibiotic (coward) or resistant to it (brave). There is a mechanism by which this resistance can be transferred from a resistant bacteria to a susceptible one. It is called horizontal gene transfer, and it involves an exchange of genetic material between individuals of the same generation. In the story this process is represented by the brave convincing the coward.
Sometimes the resistance to the antibiotics is lost, or a brave soldier becomes a coward. This process happen without interaction with other cowards (when the soldiers feel alone). The motion of the warriors correspond to the diffusion of the bacteria, while the growth in the new territory corresponds to bacteria multiplication.
At the very front of the army, the process of brave soldiers becoming cowardly is more intense than the convincing of cowards, and as a result the cowards win advantage. However, there are some brave soldiers in front of the coward mass, and that is why they pull the rest of the brave population, calling for them. Or in scientific terms, the resistant bacteria drag the others forward so long as they are not overtaken by the majority of the susceptible ones.
Nevertheless, the moment the braves are overcome by the cowards front, they slow down and all the brave population goes at a slower speed. This corresponds to the propagation of resistant and susceptible bacteria without any antibiotics barrier.
Finally, when the antibiotic barrier/the enemy is reached, it is only the braves who can continue, and now expand at a much larger speed, happy to fight and live in the new environment, free of cowards. However, there are some cowards who still join them in a small quantity. The susceptible bacteria or the cowardly soldiers would not be able to live in this dangerous environment by themselves, but a few of them survive on the shadow of the braves.
For more on the science of the story, see also the original research paper.
Drawing by Iantresman at en.wikipedia [Public domain], via Wikimedia Commons. PD-US.Source: William Howitt, John Cassell, John Cassell’s Illustrated History of England: From the earliest period to the reign of Edward the Fourth., Editor: John Frederick Smith, Publisher W. Kent and Co., 1857. Page 6.