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Subway evolution: What lurks below

About the author

Described by the Times as “the world’s most enthusiastic man” and the Daily Mail as someone whose “wit and enthusiasm can enliven the dullest of topics”,  Quentin is a broadcaster, film critic and author best known for presenting the UK's most listened to science programme, The Material World on BBC Radio 4 . It’s “quite the best thing on radio”, according to Bill Bryson. You can find him on Twitter at @materialworld

Railway tunnel, China (Copyright: Getty Images)

(Copyright: Getty Images)

The tunnels beneath our city streets are evolving and so are the life forms that live in them. It all sounds like the plot of a horror film, writes Quentin Cooper.

Down in the underground, things are evolving.   Not just evolving, going Wilde. It was good old Oscar who in 1889 came up with the much borrowed and adapted line “Life imitates Art far more than Art imitates Life”. If you want an example of such mimicry, look no further than Mimic.   

Remember Mimic, the late 90s Guillermo Del Toro film in which strange giant insectoids begin appearing in the Manhattan subway system? It turns out that it’s all the result of scientists’ misguided attempts at eradicating nasty disease-carrying cockroaches by genetically engineering a mutant bug to wipe them out.    The designer creature does the job, but then continues to evolve into something far more alarming. Which is what generally happens in movies anytime genes get tampered with.

In Del Toro’s hands Mimic is a preposterously entertaining thrill-ride with plentiful clever touches. The funny thing, though, is that a real-life version of the same story has been playing out in the same locations. Something which seems to have evolved in underground railway tunnels and that feeds on humans has managed to work its way up through Manhattan basements and air vents and out to the inhabitants of the Upper West Side. A lot of people have been attacked.    

Plot twist

When the invasion began in late summer 2010, it was soon clear than they were being caused by huge numbers of what CBS described as “extra blood thirsty” mosquitoes, but the real surprise was the finding that they were a type previously almost unknown in Manhattan. Culex pipiens molestus (the molestus bit being that they molest us more than ordinary mozzies) is more commonly known as the London Underground mosquito, a distinct species that was first identified in the city’s tube tunnels but which has now been found in many other subway systems across the world.    

The same creature diverging over time to develop an above ground form and a more dangerous close relative which ekes out its existence in tunnels below the surface has definite shades of the Eloi and Morlocks from HG Wells’ The Time Machine. Quite when and where this happened with the mosquito and its subterranean cousin isn’t clear. There is ample evidence of Londoners sheltering in underground stations during the blitz having been repeatedly bitten, but it wasn’t until around a decade ago that PhD student Katherine Byrne took the trouble to go down in the tube station at midnight and look for the insects once the trains had stopped running. 

She found plenty of pools of scummy water containing larvae, and by comparing them with mosquito larvae from up top was able – with her University of London supervisor Richard Nicholas – to establish that although outwardly similar, there were clear genetic and behavioural differences between the two varieties. For starters while the ones above ground hibernate in winter and usually only bite birds, the more troglodytic mosquitoes breed all year round in the warm tunnels and seem to have a particular appetite for human blood.  

There’s lots more to C. Molestus including the question of how they have spread from subway to Metro to Tube across the world.   But in the last few days there’s been a twist to the story that Guillermo Del Toro himself would have been proud of.  It seems the mosquitoes aren’t the only unexpected development shared between different underground rapid transit systems. The systems themselves are evolving, and evolving to become ever more alike.

A paper in the latest issue of the Royal Society journal Interface details how researchers at France’s National Centre for Scientific Research have carried out a mathematical analysis of 14 of the world’s largest subway systems. They discovered that despite differences of geography and economics and scale and a lack of co-ordinated central planning, they all appear to be converging on the same overall network structure. Some similarities are only to be expected – a core with lines branching off it may be obvious as well as functional, and later transport engineers are likely to have been influenced by the work of earlier ones – but there are others which are harder to explain.   Such as all the different subways where the distance from the city centre to its furthest station was twice the diameter of the system’s core. Or the total number of stations again and again being proportional to the square of the number of lines.

There are suggestions that at the very least this is evidence of urban evolution and self-organisation, and that it could even help us to build cities which have the capacity for self-improvement. Perhaps.  In the shorter term the idea of an ever-evolving network of tunnels sounds like a scary subterranean variant on the changing corridors and stairs of Hogwarts or the hotel in recent Dr Who episode The God Complex.   So is that art mimicking life or something deeper?

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