London Taxi drivers are among the most highly trained in the world. Not only are they carefully screened for criminal offences and a clean driving record, they must know some 25,000 streets within six miles of Charing Cross Station in central London.

This is called “The Knowledge”.

The Knowledge does not come easily. A prospective cabby is given “The Blue Book”, a detailed listing of some 400 “runs”. A run is a trip between two well defined locations in London.

Its not possible to learn these runs simply by memorising them from the book, and in fact this is actively discouraged. Prospective cabbies must actually ride the streets of London on a scooter for anywhere between two and four years, gaining firsthand knowledge.

The prospective cabby must, upon request, be able to not only identify the quickest route to take a customer from point A to point B in London, but also name the major cross streets that are passed.

During their training prospective cabbies will make several 15 minute “appearances” before a Taxi Examiner. The Examiner will ask the cabby to answer a hypothetical question, such as “I’m at Picadilly Circus it is 5PM, and I’d like to go to the London Planetarium – what's our route?”.

And the prospective cabbie must answer in the following form, which is intended to ensure that she / he has not only travelled the route, but done so at different times of the day or night, and can visualise a route and think and plan ahead:

  1. Identify the location of the pick up point and the destination.
  2. Since some streets of London are one way only, the prospective cabby must begin the route by saying "leave on the left/right", This is so The Examiner will know the direction to be travelled.
  3. The prospective cabbie must then detail the route by naming every street travelled, identifying the direction of travel as well as any traffic diversions or one way streets.
  4. When arriving at the destination, the prospective cabby needs to give the passenger setting down position by saying " set down on the left/right", depending from which direction travelled.

As you can see, it’s pretty involved. The Examiner carefully tracks progress (or lack of progress), and can recommend that the prospective cabby repeat any run or a set of runs.

In addition to the aforementioned streets, cabbies must also know the location of all hospitals, police stations, courts, government buildings, train and underground stations, parks, as well as all tourist attractions.

It takes about four years to complete “The Knowledge”, at which point the prospective cabbie will have one more examination, determining if he or she will be licensed and can work – that is, pick up passengers in the streets.

Taxis in London are regulated by The Public Carriage Office, which was established in 1850. Following the Great Exhibition in Hyde Park, a public outcry about the ignorance of the city displayed by many cabbies led to the formal introduction of “The Knowledge of London” exams.

Today there are about 20,000 licensed cabbies in London. And having read this far, you might be wondering how brain mutations enter the picture.

Some researchers at University College London examined the brains of a large number of cabbies using magnetic resonance imaging (MRI), comparing the results with non-cabbies.

They focused their examination on the hipocampus, which is important for memory formation as well as the processing of spatial data.

They found that London cabbies had larger posterior hippocampi and smaller anterior hippocampi.

Also, researchers found these size differences apparently changed over time, suggesting that their training – “The Knowledge” – actually caused changes – mutations” - to the brain's physical structure.

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