Zebra stripes evolved to keep biting flies at bay
http://www.bbc.co.uk/nature/16944753
And now, for something completely different: a man with three buttocks. (Monty Python didn’t always fire on all cylinders, but they did provide some highly memorable lines!)
While the conclusion that it was evolutionary pressure that drove zebras to develop stripes is quite questionable (as the end of the article alludes), it is none-the-less quite an interesting idea. Since every animal isn’t zebra striped it clearly can’t be a huge advantage, but there are plenty of things that evolve for no other reason than the female of the species has happened to take a liking to something. So it might be a simple coincidence that zebra stripes lead to fewer fly bites, but that got reinforced, perhaps, because girl zebras were happier with boy zebras that spent less time prancing around in agony from fly bites (and I mean agony, those damn things feel like they are carving a cubic inch of flesh out when they latch on to you).
I wouldn’t quibble about it being a small, secondary benefit, but I would opine that if it were major enough to have biased all zebras to be striped, we would have a lot more striped animals than we currently have.