Well, ancient Greek writers described unicorns as being about the size of rhinoceroses, and having elephant-like feet... which sound very much like a description of Elasmotherium sibiricum, which was recently (re)discovered as a 29,000 year old fossil in Kazakhstan.
And then, there's the example of the roe deer that was born in a park in Italy, and discovered in 2008 (pictured in my icon, here) -- that was probably the result of a variation in the gene nicknamed "Sonic Hedgehog Homologue," which governs the growth of appendages: when it's stronger than normal, you get things like extra-toed cats, and if it's weaker than normal, you get creatures (including humans) born with missing or partially-grown limbs.
And it's also possible to create unicorns, surgically. In 1933, biologist Dr. William Franklin Dove transplanted the horn buds of a young bull calf from the sides of its skull to the center, and the two buds grew into a single straight horn. And the same surgery works with similar results for sheep and goats.
My own guess is that occasionally, someone would come across a wild deer with a single horn, and its rarity and striking appearance would lead people to assume it had magical powers, and symbolic meaning.
Followed later by shepherds and herdsmen giving surgically altered animals as gifts to the local lord or king -- perhaps the "Two horns merged into one" as a symbol of the ruler's power to unite warring factions.
Followed still later by diplomats and dignitaries returning from royal visits, and describing the exotic animals they saw inhabiting the royal gardens...
I think the unicorn acquired the horse's body because horses were deemed a more "royal" and "noble" animal, while sheep and goats are animals associated with peasants.
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And then, there's the example of the roe deer that was born in a park in Italy, and discovered in 2008 (pictured in my icon, here) -- that was probably the result of a variation in the gene nicknamed "Sonic Hedgehog Homologue," which governs the growth of appendages: when it's stronger than normal, you get things like extra-toed cats, and if it's weaker than normal, you get creatures (including humans) born with missing or partially-grown limbs.
And it's also possible to create unicorns, surgically. In 1933, biologist Dr. William Franklin Dove transplanted the horn buds of a young bull calf from the sides of its skull to the center, and the two buds grew into a single straight horn. And the same surgery works with similar results for sheep and goats.
My own guess is that occasionally, someone would come across a wild deer with a single horn, and its rarity and striking appearance would lead people to assume it had magical powers, and symbolic meaning.
Followed later by shepherds and herdsmen giving surgically altered animals as gifts to the local lord or king -- perhaps the "Two horns merged into one" as a symbol of the ruler's power to unite warring factions.
Followed still later by diplomats and dignitaries returning from royal visits, and describing the exotic animals they saw inhabiting the royal gardens...
I think the unicorn acquired the horse's body because horses were deemed a more "royal" and "noble" animal, while sheep and goats are animals associated with peasants.