The first gene would have been an organism capable of replicating itself, with error. DNA is a high-tech replication process and the current theory is it may have been RNA. While DNA is an amazing replicator, and protein is an amazing enzyme, RNA is capable of poorly playing both roles.

There is overwhelmingly strong evidence that all life on Earth is descendant of a single common ancestor as every examined organism shares a universally identical DNA code and the likelihood of that coming about convergently is miniscule.