"Common descent is a general descriptive theory that concerns the genetic origins of living organisms (though not the ultimate origin of life). The theory specifically postulates that all of the earth's known biota are genealogically related, much in the same way that siblings or cousins are related to one another."
Grand theory with absolutely no empirical evidence to support it. This is based on speculation because all life on Earth share genetics in common. They can't explain why that is, just that it is.
Except for genetics (including ERV insertions), biogeographical distribution patterns of living species, morphological evidence, thousands of transitional fossils, ring species, etc. - the list keeps going. I'm guessing you didn't read through very much of the link I provided (though I may be wrong).
Not only that, evolution makes specific, testable predictions, just like any other valid scientific theory.