system
Given the following post, respond as if you're commenting on Reddit:
human
Have we ever found a species which does no fit into the genetic "tree of life"?

A species that doesn't have any genetic connection to any other species basically. One which could have come to earth on an astroid possibly.
gpt
The short answer to this is no.  

All living things (I am excluding viruses from this discussion) are composed of cells surrounded by a membrane. They also all use DNA to store the instructions necessary to create proteins. Given these similarities, scientists have concluded that all life on Earth shares a common ancestor. It is important to note that this does not preclude the possibility that life *originated* elsewhere however.  

Since all life must perform many of the same functions (DNA replication, protein synthesis, metabolism), there is a subset of genes that all currently known living organisms possess. One of the most well-described of these genes is is the ribosomal RNA (or rRNA) gene. Similarities in this gene are used to determine the "relatedness" of two species since parts of it are not under selective pressure and can mutate at a (somewhat) predictable rate.