Common descent? Universal common descent? What the diff?
|August 30, 2013||Posted by News under News, Origin Of Life, speciation|
On the Intelligent Design Facebook page, a discussion developed, courtesy Timothy Kershner, on common descent, as understood by ID theorist Michael Behe. A question arises about common descent vs. universal common descent, and a distinction seems worth making.
Common descent is the sort of thesis which needs only sufficient evidence to be a reasonable hypothesis in a given case. If dogs, wolves, and coyotes can interbreed, common descent is a reasonable explanation. Maybe all frogs can’t interbreed, but common descent might be a reasonable account of similarity in their genes and body form.
Of course, where life forms look very much alike but have significantly different genes (like the olinguito), we do have a problem. The problem warns us not to make common descent into some kind of ideology (a warning many will be proud to ignore or think it their duty to ignore).
And by the way, it is no use to say, “Well how else could it have happened?” If there can be evidence for any proposition, there can also be evidence against it. And we may not have anything like the information we need in order to assess the preponderance of the evidence at this time.
Universal common descent—that all life forms arose from a single cell—is more of a radical philosophical claim. It can’t really be demonstrated; in any event, the differences between the bacteria and the archaea, among others, have suggested to some researchers that it isn’t even likely.
The sheer unlikelihood of life coming to exist at all is not an argument for universal common descent; it is an argument for a non-random origin of life. If a random origin of life were true, however, early life could have arisen a number of times under favourable conditions, with the individual nascent life forms having no necessary familial connection with each other. A person who is philosophically committed to universal common descent must reject that account on purely philosophical grounds, because there may never be definitive evidence one way or the other.
On the whole, limited, demonstrable common descent is a more reasonable and less contentious claim.