Question

Why do we exist?

Answer 1

We exist because of the concept of evolution. According to an evolutionary biologist Richard Dawkins, Gene is immortal and the coded information they contain is reproduced, is replicated with almost total fidelity. Significantly not absolutely total fidelity. Generation after generation the gene carries the coded information and difference between the successful gene and unsuccessful gene really matters. An individual is a throwaway survival machine for self-replicating coded information which it contains and the fate of that coded information is crucially bound up with the fate of the body in which it sits.

If the body in which it sits dies before reproducing then that coded information is not going to go on to the next generation. So, the genes in the world today distributed as they are in bodies of millions of different species including humans are here today because they were good at what they did in the past. They have come through the unbroken line of successful ancestors. Hence, genes are immortal and the successful genes go to the next generation and evolve whereas the unsuccessful doesn't.

Another concept of why we exist is due to free will which is described in the theory of Existentialism which is a philosophical approach.