What strikes me about the question and the theoried answers is how the premise behind the answers are leading. “Why” is assumed to be answered by a Darwinian motivation, survival. The stripes must (we assume) contribute to their competitive advantage. The “why” can’t include, we imagine an aesthetic motivation, which is probably a principle motivation by us for our interest in them. We do the same with beautiful birds or insects talking about mating advantages, etc.
This isn’t to say that there isn’t validity in all of that, but consider the opposite. Why are there so many counter-productive elements in biology? Why haven’t we evolved beings to not die? Why don’t we reproduce more? Why aren’t we stronger, faster, etc? Surely all of these things would be beneficial to our survival? These questions we don’t ask. Why not?
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These are very interesting questions, they actually do have answers:
Stripes can occur by accident, and this even happens in humans:
http://io9.com/5963790/humans-have-stripes-you-just-cant-see-them
If striped individuals had some other quality associated with them eons ago, e.g. strength or speed or resistance to disease, then many animals would seek out striped mates and cause it to be endemic.
About aging, there simply hadn’t been a natural selection for old age up until recently. Since the evolution of humans people tended to be killed very young by disease or warfare, the expected lifespan was about 30. Genes that conferred short-term advantages were selected for, even if they resulted in the brain declining in old age, because too few humans got old enough for it to matter. It’s still the case, we’re slowly pushing it farther by having babies later and later in life, this is selection in action that is synthetic, like dog-breeding.
We don’t reproduce faster because human babies develop slowly compared to other animals, as our large brains take a long time to grow. The longer babies stay in the womb the better-equipped physically they are when born, as the baby is fed perfectly when in the womb at the expense of the mother’s health.
The development of human musculature is too detailed to go into, but essentially we evolved to do long distance running without much food or water which required that we not carry heavy muscles or excess bone, so the weaker humans were selected for.
In scientific circles these questions are definitely asked, evolutionary theory had extraordinary levels of detail about just exactly what we are as humans (or zebras), it’s well worth a look!
Thanks. That was very helpful! 🙂