Thus, if there is some basic DNA-bearing life-form that spread around the universe, all sorts of variants could have sprung from it, each recipient planet thus giving rise to a unique evolutionary tree. So maybe the whole idea of extra-terrestrial aliens having DNA that could be compatible with our own, is not so crazy after all. I still think the idea that ETs could successfully mate with early humans is highly improbable, in terms of basic biology, but there could still be some genes that they could give to us that might give us extra abilities.
This video is also interesting where they talk about completely sterilizing the spaceships that go out into the solar system to look for new life, so that if new life is detected on say Mars, it can't be from contaminating earth bacteria. This procedure seems a bit silly to me, since it should be easy to look at the DNA of some ET bacteria or other ET life form and see if it is remotely like anything on earth. Any true alien life should be significantly different from life on earth.
However, sterilizing spacecraft to remove earth DNA, interestingly fits with the idea of the earth quarantine, where ETs monitor craft that leave the earth, and prevent any humans from leaving. Spacecraft without any DNA have a better chance of escaping quarantine, perhaps?
On this note of panspermia, and bacteria surviving in tough climates, is this awesome 33: