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The ancestor of all the backboned animals – including humans - is a sea squirt that looks like little more than a bag of jelly. Incredibly, 80% of its genes are inside us too - including those that form the human heart. But where is the backbone? The key to that inheritance is found inside its tiny young. These little squirts have a tail with a flexible rod inside that is the earliest hint of a backbone. With this flimsy backbone the first true vertebrates emerged. Amongst these were the ‘jawless fish’. Jawless hagfish are deep sea creatures that live way beyond our reach. More than a mile below the ocean surface, they are scavenging on the carcass of a dead whale. Despite looking more like worms than fish, jawless wonders like these ruled the seas 500 million years ago. Today, they sometimes rise up in to the shallows, and in Sweden’s cold dark fjords they come face-to-face with fishermen. If they are caught by a predator, their primitive backbones are so flexible that they can literally tie themselves in knots. Made of cartilage instead of bone their spines are much bendier than ours. And if tying a knot is not enough to escape the predators grasp then the hagfish has another defence mechanism up its sleeve. The hagfish secretes mucus from glands either side of its body and this mucus starts to swell when it contacts water. It also contains hi-tensile fibres that form a shield of slime. One hagfish can jellify a whole bucket of sea water. But, despite these extraordinary adaptations, jawless fish had soon had their day.