Spirit really interests me. As far as I can figure it out, 'spirit' is universal in humans and, apparently, in other great apes.
If spirit is the inner wisdom we hold, which you might say is 'god in man', it is probably genetically coded knowledge that helps us to survive, to maintain societies appropriate to our species and to rear our young. As far as we can tell, all creatures have it. Compassion, for example, has been observed in a wide range of creatures previously thought to be 'dumb', as have empathy and wiliness.
If spirit is creativity, the same applies. Possibly sheep don't have much self-awareness, but they can still solve problems and communicate. Creatures engage in sophisticated behaviours to various levels, can adapt to changed environments, use tools in new ways and some make art for art's sake.
If spirit is personality - it's the individual character, made up of genetic inheritance plus experience. The personality is unique. It dies when the brain dies. The other qualities, though, are passed along genetically if the individual reproduces. So, in a way, the 'spirit' is immortal as long as there is life. But the personality is the product of a unique set of circumstances, and lives only once.
I find this amazing! But it might not be what religious followers mean when they say 'spirit'.