@pnelson do you know of anyone who simultaneously:
Affirms the common descent of humans with the great apes.
Denies the common descent of all animals with one another.
Do you know any one that holds both views? If not, aren’t these questions about the boundary conditions of UCD a side issue? What is your best case against the common descent of man, where we have most of the evidence? If there is no solid case against it, why would we worry about more murky details from hundreds of millions ago?
Note the base of the web. If these multiple cellular starting points are independent of each other, their shared molecular characters do not trace to a single common cellular ancestor. The consequences for phylogenetic inference in that case are profound.
It’s not the distant murky details that are most important: it’s how phylogenetic inference works, and how its logical structure changes dramatically, once once surrenders UCD. Of course (T aq., pay attention) Doolittle and Bapteste retain the common ancestry of the animals. (Frankly to do otherwise would risk condemnation as ID sympathizers.) They are not following out the full implications of their own anti-UCD position.
T. aq and several others here have called UCD “a red herring.” Actually, UCD could not be more central, but I fear the only way I’ll explain that is by posting a full-length talk (in pdf format), so readers here can follow the logic step-by-step. Hoping to do that soon, after I return to my office in Chicago.
We’ll have to bracket that question for the time being. My opinion-in-brevis: we have evidence for the similarity of human and chimp (and other higher primate) DNA.
But what we don’t have evidence for, or understand, is how the apomorphic characters which define H. sapiens are (a) located in human DNA, when compared with chimp DNA, or (b) how those characters evolved in the time available since our last common ancestor with chimps. Given that these transformations are the main empirical claim of common descent, I’d say the evidence for the common descent of H. sapiens is less than overwhelming.
A conversation for another time. My break here at Louisiana College will soon be over; more guest lectures loom.
If there were three origins of life for eukaryotes, prokaryotes, and archae how would this change the evidence for humans and chimps sharing a common ancestor?
We have a phylogenetic signal for morphology and DNA among primates. It isn’t simply similarities.
Do you have any evidence that the differences between chimps and humans is not due to the DNA sequence differences between their genomes?
The theory of evolution has DNA differences arising through the known and observed mechanisms random mutation (with respect to fitness) and vertical inheritance. How are these not sufficient?
I think there’s a pretty big difference between questioning some of the phylogenetic inferences at the base of the tree of life and questioning the inferences within the animal tree.
Can you elaborate on this? What exactly do you want to see?
Could you drop this kind of backhanded suggestion about other people’s motives? It contributes nothing to the discussion.
I have used common descent repeatedly in my work, and I see it used all the time in a wide range of biological studies. I can’t recall ever seeing any work that relied on UCD. If UCD is central, it’s central in a completely peripheral way.
It seems to me that pretty much every ID proponent accepts some type of common ancestry. So I’m puzzled why they spend so much effort arguing against it. Someone like @Agauger who thinks human evolution took place at the level of Genus for example, that’s at least two million years of evolution and some of the relationships within our genus are foggy and unclear. Why not publish work on this? Try to give us a clearer phylogeny for Homo. I think that would earn them some scientific creditability as well. Their effort is mostly misplaced.
I suppose you could say every ID proponent accepts some form of common descent. I don’t know, But the boundaries are hazy. What constitutes common descent? Within a genus? Family? Order?
We are working on something to publish. How about you @swamidass? I doubt it will earn us credibility.
Since I’m obsessed with our genus and how our species has evolved and adapted since our origin (no matter how we arose) I would most definitely be interested in any work you guys do in that area. Just right now yalls work seems very us against them. I think if you guys also did work where you share common ground with mainstream biology it could ease some tension.
Shouldn’t you guys be trying to figure this out? @AJRoberts thinks it will probably vary and all the work I’m seeing from baraminology/discontinuity systematics is the most common boundaries hover around family and order.
Why does this question need to be bracketed for the time being? Seems like a pretty easy question to answer, given all of the evidence for common descent of man.
At least to me, common descent means sharing DNA through vertical inheritance just as my siblings, cousins, and I share DNA through common ancestry. Any grouping above the species level in Linnaean taxonomy is arbitrary, so I wouldn’t put too much stock in those categories.