In the search for a cure for colour blindness scientists have potentially stumbled upon the secret to extending the visible spectrum of the human eye. We can all see ultraviolet reflections from white or other fluorescing surfaces and IR cameras let us “see” infrared on the plethora of police documentaries… but the naked eye has its limits. Other creatures naturally possess a wider perception; many reptiles, birds, fish, arachnids and insects are tetrachromatic and seeing ultraviolet (UV) in addition to the red, green and blue we can see. Some birds (notably pigeons) and butterflies have five colour receptors – making them pentachromatic and the carp family including the humble goldfish can see infrared which scatters less in murky water.
We are trichromatic (though our genes show this was not always the case) detecting a tiny part of the electromagnetic spectrum which we arrogantly call “visible light” via three types of cone shaped receptors on the retina: L-cones for Long wavelength light (Red, orange, yellow), M-cones medium wavelengths (green) and S-cones for short wavelength (blue). Each of these is paired with a protein called an opsin which reacts when light hits the cone (photoreceptor) – they are, quite logically called L-opsin, M-opsin and S-opsin.
In September 2009 research was published in the journal Nature (Vol. 461) which details the genetic addition of the missing photoreceptor protein to the dichromatic retinas of red-green colour blind monkeys. The male squirrel monkeys used in the experiment are naturally dichromatic and only had M and S cones present on their retinas, no L-cones or or L-opsin protein gene. Using a touch screen with the Ishihara bubble patterns we’re all used to seeing at the opticians the monkeys were given rewards whenever they got the correct answer – they were unable to see diagrams intended to test for perception of reds.
The monkey’s retinas were injected with a virus containing a gene to produce L-opsin and after 20 weeks, despite the lack of L-cones, they began to see the diagrams for red-green perception. This raises some fascinating possibilities, first and foremost a cure for a condition which prevents people from pursuing certain careers where the colour blind are excluded. It has also caused scientists to revise their views on neurological “plasticity” (the ability of the brain to adapt to new stimuli) since previous experiments seemed to indicate only the very young exhibited this trait – but these were adult monkeys. Somehow the presence on the L-opsin has altered the data from the existing receptors and the brain has found a way to extract additional information from the new data stream.
Most intriguing of all, however, is the thought that if a dichromatic creature can gain a third colour, then a trichromatic one could regain the fourth colour lost during the evolutionary process. You seen there are actually two S-opsins – one for blue (SWS2) and one for violet and UV (SWS1). What would happen if a human could produce both of these? How would the world look – you’d need very dark sunglasses for a start! The UV dyes from bank dye packs and Smart Water sprays would make it impossible for thieves to move among us unnoticed as the super cops would be among the first to receive the enhancements. It’s worth making the distinction here between the reflection of UV light which we can’t see and fluorescence which we can. Fluorescence is the emission of visible light in response to light of a different wavelength – what you see in a night club is UV which has had its frequency lowered into the part of the spectrum we can see. Actually not very many objects reflect UV light – water, mirrors, the centre sections of flowers (to attract insects). Car headlights with UV (8000k colour temperature) cause road signs and white lines to fluoresce – this genetic enhancement would also make directly reflected UV visible.
To me, though, the most startling of all is the possibility of adapting the carp genes to allow us to see near infrared. Imagine rescue workers in an earthquake zone able to see the silhouette of a trapped person under the wreckage of a a collapsed building or floating in the water from a tsunami. Your doctor would see the heat from your torn muscle or ligament, the swelling of at insect bite, maybe even the altered blood flow caused by a tumour or skin cancer. We could all insulate the areas of our houses which leak heat in the winter without the use of expensive cameras and architectural design would naturally evolve as a result of observation. You could see that dodgy burger on the barbecue and ensure it was heated all the way through. The possibilities for good are absolutely vast.
The possibilities for less altruistic use are fairly obvious – the super soldier. Our pentachromatic warrior would be marked with invisible UV designators like the felt tips we use to mark valuable goods to avoid blue-on-blue attacks (no pun intended) – a good thing – but will also able to see an enemy through undergrowth, camouflage netting, wooden buildings or partition walls.
We don’t really have a choice, these things will happen, I just hope the rescue workers and super doctors outnumber the soldiers and assassins.
References:
Gene therapy for red–green colour blindness in adult primates.
Wikipedia Evolution of Colour vision in Primates
Wikipedia Tetrachromatic Vision
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