Is near-universal common descent detectable?

@John_Harshman, please take this as a good-faith question, I’m not trying to prove a point or argue, just get some clarity.

Partially because of what I learned about genetic ghosts, etc. reading GAE and partially because of my own view of how science operates (absence of evidence isn’t evidence of absence), I’m a bit suspicious about the idea that we know scientifically that common descent is completely universal. Is it not possible to have, suspending the question of God’s existence for a minute, special creation of individual organism and perhaps lineages, that would not be observable to us today in the DNA we have access to? I would guess it would have to be limited, but it seems like it would be impossible to rule it out completely, right?

Maybe another way to put it is that we see the signal of common descent in the DNA we have access to, but since we don’t have the DNA of all organisms throughout time, what limitations might there be on the universality of common descent?


It’s certainly logically possible. I don’t think it’s physically possible, but let’s accept for the sake of argument. Well of course God, being omnipotent, could create anything he liked. There’s no way to test for separate creation of species under such a model, just as there’s no way to test for Last Thursdayism. It’s conceivable that every species in the family Corvidae evolved naturally with the sole exception of Cyanocitta stelleri, which was created de novo, ex nihilis. But why should we entertain such a notion?

There’s more evidence than just DNA, of course. There are fossils too, and they still fit into that nested hierarchy, show a stratigraphic and geographical pattern that tends to make sense. I’ve mentioned mass extinctions before, but they work here too: why would God create so many species and higher taxa only to destroy them abruptly en masse? Did he just get tired of trilobites and decide to concentrate on beetles instead? Common descent fits all the data we have. Separate creation, to the extent there are any expectations whatsoever, does not. You can always save it, though, by appealing to a deceptive God.

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@John_Harshman, thanks for the reply. I am thinking on a bit different scale. Iwas thinking less about whole species de novo, ex nihilis but rather maybe something more along the lines of individual organisms or small populations that might change/bias allele frequencies somewhat. It seems like that would look like statistical noise if it was small enough. In other words, what if God “nudged” evolution around a little in specific directions.

I’m thinking here of something like local maxima in a fitness landscape. If evolutionary processes are humming along and a “special creative act” changed allele frequencies within a species to nudge a population toward a particular local maxima, would that even be detectable? I would consider that a near-universal common decent or an “effective” common descent.

It just seems to me that it would just be “in the noise” and we wouldn’t know anything about it.

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Sure. There could be no evidence for or against, if he’s careful. But why would God hide so? What’s he afraid of?

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I wasn’t thinking of it in terms of being hidden. I was thinking of it as God being generally content with the system that he brought into existence (Big Bang, evolution, etc.) but also perhaps sometime desiring or choosing a particular path when multiple options existed (localized maxima).

I think this is one of the ways people have though about a purposeful human evolution. God created a universe in which complex life could form and evolve on its own, but perhaps he had a particular organism (who developed consciousness, language, spirituality, civilization) with which to enter into relationship with. People sometimes harp on what “God-guided evolution” would mean, I was just exploring that a little.

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Again, there can be no evidence for or against such a proposal. We are left only with Occam’s razor, which you may take or leave.

It seems over-elaborate. Why not just mandate a few mutations here and there, without the need to create entire adult (presumably) organisms? That’s especially problematic in species with long-term parental care involving extensive learning. God would need to create false history in the memories of the created hominids.


Yep, good points, thanks!

That itself is a bit over-elaborate.

Why not just have all the inputs required at moment of creation, rather than having to nudge it over and over again?


Agreed. If there’s a local maximum and a hill for selection to climb, what do you need nudging for in the first place? It’ll get there automatically unless the hill is very far from the starting point and the steps to get there are and always remain effectively neutral or deleterious. But then it seems God has made the intermediate steps deleterious or neutral on purpose, so why would he do that if he intended some organism somewhere to reach that local maximum in the first place?

If God created the universe and the laws of physics, he’s ultimately responsible for setting up the conditions that would come to define shape of the fitness landscape at all times to all organisms on all planets, so you have to wonder why he’d structure it such that to get certain places on it would require him reaching in to nudge stuff around to specific locations, rather than employing his omni characteristics to set up the whole theatre to produce what he wanted from the beginning.

From that perspective I can appreciate a theistic view of evolution along the lines of things Michael Denton have argued in the past - that life’s origin and evolution were essentially unavoidable consequences (“Nature’s destiny”) of the laws of physics - much better than the Michael Behe-IDcreationist view that requires God to poof certain things like flagella or feathers into existence. The Denton-style view also seems more compatible with fine-tuning style arguments. There’s a degree of coherency to that view that the God as a fiddler/nudger lacks.


That is a position which some advocate. :wink::sweat_smile:

Sure. Why not, in fact, create the world in the state you want it to be in and forget about evolution altogether? If you want humans, just make them directly. If you don’t want anomalocariids for the final state, why bother making them at all?


Come now, we’ve all known people who are very obsessive and fussy and insist on doing things in this particular way, even though we point out to them that it would be much easier to do them in that particular way. Same here.


Maybe God really likes evolution from common descent! :grinning:

And I agree with him. If only the creationists would decide that.


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