The paper's author, Duncan Caldwell has surveyed the Paleolithic art of several caves in France and discovered a recurring theme that he says can't be simply accidental. Throughout the cave of Font-de-Gaume, and in examples from other sites as well, drawings and engravings of woolly mammoths and bison often share certain lines or other features, creating overlapping images that can be read first as one animal, then the other. Rarely, if ever, do they do the same with other animals.
While images of horses, deer, extinct cattle, and even rhinos often appear in such caves, and often partially or entirely overlap each other, it is only the mammoth-bison pair that Caldwell found regularly appearing superimposed so exactly. For example in the modern drawing below of an image from Font-de-Gaume, one main body shape, underbelly, and set of legs is adorned with signs of both mammoth and bison heads at both ends. These two large, bulbous, "armor-headed herbivores" which share many physical similarities in life, seem to have had some connection for people in this region in art as well.
In a particularly striking example, a small figurine has been given the details of a bison on one side and those of a mammoth on the other. The Paleolithic artist was clearly playing with the similar contours of the two animals and creating a single object that could be flipped to represent one species or the other.
Nice Trick, But Is It an Illusion?
There's a big difference between overlapping images or ambiguous profiles and a proper optical illusion however. Nigel Warburton is a senior lecturer of philosophy at The Open University and co-host of the podcast "Philosophy Bites," which uses the duck-rabbit as its logo. For him, knowing the original context of the image is key. Speaking of the classic version, he said "If somebody had been illustrating a children's book about rabbits, nobody would have seen it as a duck." As he put it, "the fact that a figure can be read in two ways isn't conclusive proof that it was intended to be read both ways."
The duck-rabbit is different because we know that it was created not just to show both animals individually, but to call attention to the strange sensation of one replacing the other. It's to some degree a "reflection on the nature of perception." The mammoth-bison images clearly make use of ambiguous shapes and similarities between the animals, but that doesn't guarantee they were intended as optical illusions.
Source from http://blogs.nationalgeographic.com
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