First I want to make it clear that when I say Common Descent
I am talking about all of today's diversity of living organisms owing their collective common ancestry to some unknown population(s) of single-celled organisms.
Next it should be pointed out that there is more than one flavour of Common Descent
. There is at least CD via the blind watchmaker and CD by design.
And finally that evidence for Common Descent
relies heavily, if not solely, one the similarities
observed but says nothing about the differences, except to note they exist.
The evidence demonstrates a diversity of living organisms exists today, on this planet. The question is (if not by Common Descent) How did that diversity come to be?
1) A separate and special Creation of differing populations with the built-in variation that would allow for adaptaion into environmental niches as they present themselves.
2) A separate designing of differing populations...
3) Colonization by an existing and perhaps dying civilization- including various modes of terra-forming
1 & 2 are very similar with perhaps only semantic quibbling being the difference.
3 may appear to push the "issue" back, but I say the "issue" is living organisms on this planet. IOW first deal with what we have in front of us.
Now some people may say that special Creation isn't science. However if science deals with reality and special Creation is that reality, it has to be science and everything/ anything else would be science-fiction at best.