Very good and apposite question. Briefly, it depends in part by what we mean by “common descent”… I don’t harbor nearly as strong an objection to biological/reproductive common descent itself as I do to the supposed mechanism of common descent… whether in human ancestors, across Other species, or all the way from an original single-called organism to man. I have my reasons for doubting it - partly because there seem to me alternate legitimate hypotheses (which I’ll outline below), but my doubt or rational objection is not nearly as strong as to the “random mutation + natural selection” mechanism itself.
But if by “common descent” we mean it in a broad sense, I essentially have no objection whatsoever…
-
Firstly, common descent is largely predicated on the supposed mechanism of small, minute variations accumulating and directed by natural selection. If this were somehow fully disproven, at least one plank of the larger biological common descent hypothesis would be removed.
-
that said, I can conceive the basic logic of a process (I believe as embraced by Behe) where God (or whichever designer) allowed evolution to proceed, but then at various points introduced by some direct manner certain radical, fully formed, complete innovations. I don’t have any particular rational or scientific objection to this hypothesis, as I do the blind natural selection/random mutation mechanism.
-
Thirdly, though, I could conceive, hypothetically, of a process wherein the essential design or blueprint of any certain organism was a starting point, and a designer made heavy modifications (mentally or otherwise) to the design, and created new organism de novo, but with heavy reliance on previous design, making required modifications. (This, and the above, seem like they would be relatively consistent with the “punctuated equilibrium” hypothesis of Gould, by the way).
-
also a bit odd, but variations on the above, I could conceive hypothetically of the design going in the reverse… that man could have been the first organism conceived, then as the design process unfolded, we kept modifying that template to achieve the lesser organisms. Or even many various designs informing each other all at once.
The third bullet above by the way is essentially how we do things in the engineering world. I can walk through various classes of submarines, and see lots and lots of identical components, systems, structures, designs, etc. Or one could do it with automobiles. obviously one can take a bunch of automobile designs, examine them in detail, and perceive and outline The “common descent“, based on introduction of new features, vestiges if previous designs, etc… obviously they didn’t have common descent in the biological/reproductive sense, but one could recognize such common descent.
I’ve observed the same in computer science. I can still (on windows 8 on my PC) pull up files that are vestiges of good old windows 3.1 back in the 90s. My favorite is “moreicons.dll”, which I often used to select different icons back in windows 3.1… and which I can still use for more icons to this day in windows 8. and half the icons reference “MS-DOS.” a vestigial item if I’ve ever seen one!
So yes, I’m the broad sense, there is unquestionably some kind of “common descent” in submarines, automobiles, and software programming. And I would wholeheartedly endorse the same in biology. I remain a bit dubious of the core biological /reproductive common descent, only because, logically, we’d have to somehow remove the other competing hypothesis (of common design). And the other half of my skepticism comes from the fact that scientists… whether atheist or EC/MN devotees, would not even be willing to consider the other alternatives for the reasons I discussed above. I’m not willing to toss out such hypotheses so quickly. Again, they seem to be very much predisposed to only see biological common descent, as they have essentially a priori ruled out alternate hypotheses from consideration, as previously discussed.
But in short, again, no, I don’t have a very significant scientific or logical objection to common descent in any kind, including the hypothesis that a single cell was started and through whatever processes was adapted, and changed, and eventually became us people. My core scientific objection is almost strictly in the attribution of that process to the unaided random mutation/natural selection process as having the ability to achieve such changes.