EUGENE, Oregon – It is accepted in track and field, both in silence and aloud, that there will likely never be another Usain Bolt. There will never be an athlete with Bolt’s ethereal combination of speed, presence and joy. Never another with Bolt’s relentless seizure of moments and of history. Never another with his ability to hoist a niche (being kind here) sport, throw it across his shoulders – or clench it in his radiant smile like a pirate’s scabbard – and make it not just relevant, but viral. He ran faster than any human, more gleefully than should be allowed, and pulled an entire ecosystem along in his slipstream. He was a unicorn.