Re: If there is a corrilation, what does it prove . . . ?
There's a revolution going on in biology. They can take two dna samples and come up with a plausible estimate of how long ago the two samples had a common ancestor (apologies to the creationists in the crowd). Work continues and the process gets better all the time.
If there is ET DNA, it will be obvious, when compared to earth DNA. So it proves whether it comes from earth or from some other source. Additionally, if it came from Mars, for example, it might still show a relationship -- one that relates Marslife to Earthlife.