Of course, we can't know for sure, but the fact that in all this time no other strain seems to have made it makes that theory implausible to me.
To be fair though, there is A LOT of life on earth, so we can't discount the possibility that we'll find some forms of life that come from a different tree than us.
To be fair though, there is A LOT of life on earth, so we can't discount the possibility that we'll find some forms of life that come from a different tree than us.