ANSWERS: 5
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Really. What would a snail, a jellyfish, or an octopus DO with a backbone?
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Because they are not vertebrates. They are in a different branch of the tree of life than we are. They split away from our genetic lineage before the evolution of the spine.
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"Why?" is always a problem to answer scientifically. There are many kinds of animals without backbones. Indeed vertebrates evolved relatively late in the history of life on earth. Invertebrates, meanwhile, have been highly successful occupying most ecosystems.
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Maybe because they don't have a back to keep it in!!:P
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b/c they dont need one!
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