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How The Zebra Got Its Stripes - Scientists Reveal All

posted 27 Dec 2013, 04:48 by Mpelembe   [ updated 27 Dec 2013, 04:49 ]

A new study into motion imaging could explain the evolutionary significance of a zebra's stripes. According to scientists in the UK, the stripes have evolved to confuse predators and disease-carrying insects by creating optical illusions.

PILANSBERG, NORTH-WEST PROVINCE, SOUTH AFRICA (APRIL 18, 2012) (REUTERS) -  A new study claims to have an answer to one of the great questions that some say Darwin's theory of evolution never answered; "How and why a zebra evolved stripes?".

Johannes Zanker and his colleague Martin How claim in a new article in the journal "Zoology" that motion camouflage is induced by zebra stripes, in the same way a horizontally spinning barber's pole actually looks like it's moving vertically, and a spoked wheel turning clockwise at certain speeds looks to be turning in the opposite direction.

Zanker, a computational neuroscientist currently based at Royal Holloway University in the UK, says the computer analysis he and How have done shows that the significance of the stripes lies in their movement.

"So basically in what the brain sees when a person or an animal looks at zebras, there are very peculiar motion illusions generated in the brain," he said.

"This is what we found, and this speaks to the long question of why do we have, well, why do we have animals with black and white stripes," he added.

The study acknowledges that the theory that the stripes act to confuse observers is the most plausible explanation for the stripes, but argues this has never been fully explained.

"Their stripe patterns confuse the visual system of a potential predator, or, let's say, equally, of insects, which are not just a nuisance to these animals, but also could be carrying diseases," Zanker said.

By using a computer modelling system which was programmed to mimic brain activity in understanding the observation of motion, the study says that the illusion of quasi-directional movement created by the movement of zebra is what confuses observers.

Footage released by Zanker and How visually represents what they say the brain interprets in motion by using colours on a chart showing direction of movement.

In the example of a spoked wheel turning, the wheel apparently turning left appears to change direction when it gets to a certain speed, in the graphic changing from red, meaning left, to green, meaning right.

Adding yellow for up and blue for a downward direction, when the zebra image is interpreted a smorgasbord of colour appears, which Zanker said means the direction in which the animals are moving is nigh impossible to tell.

"Motion illusions are discrepancies between the physical stimulus, let's say where a zebra stripe is moving, and the perception of the neural system, the representation in the brain, which could in a different direction, or which could go even in reverse, in an opposite direction to what actually moves," he said.

The brain, Zanker said, understands motion uniquely.

"It is a part of the mathematical mechanisms, the mathematical algorithms as we call them, which underlie the extraction of motion, and there are some fundamental problems with motion signals which cannot be easily overcome, and this leads to illusions like that," he said.

"So it's just inherent to how the neurons in the brain need to extract the motion information," he added.

Zanker and How believe that the computational model is the closest thing available to seeing how the brain interprets motion images.

As well as being used in creating fancy illusions in barber's poles or in artwork, Zanker said it could also be used in more meaningful ways. He argues that if zebra crossing lines were painted horizontally to approaching cars, drivers would be more inclined to notice them earlier.

"You could think about zebra stripes which could make it safer to cross a road for pedestrians, equally you could look at the painting of cars, or motorbikes," he told Reuters Television.

"Typically the motorbikes of emergency services are painted with high contrast patterns to make them more visible, which is definitely the case, but there is the question whether this could also induce similar problems with localising the direction of motion and the position of these objects, these motorbikes or cars," he said.

"Funnily enough, in the First World War, so-called dazzle patterns have been used to paint ships, to make them less visible to enemies who might want to attack them. The historical verdict on that was with mixed results," he added.

Further research is now expected, according to Zanker and How, which could focus on the distribution of different striped patterns in different animals and environments and ecological contexts and related to different kinds of behaviours.