I am happy with how well this discussion has gone so far, so I don't have any problems with what you've chosen to discuss or how you've approached it.
Yes, I'm aware of that. Sorry for my sloppy use of terms. I'm not trying to trap biology into something it hasn't claimed. Further, I'm not a biologist, so I'm open to clarifications and corrections if I misunderstand the situation.
It actually is a problem if the argument for LUCA includes fossils. At this point I suppose I should mention Elliott Sober and his book Philosophy of Biology. Sober is a strong supporter of evolution, which means I don't completely agree with him. Despite that, I really enjoy his writing. I admire the way he handles creation, even though he eventually dismisses it. I also admire that he is willing to criticize biology in ways that are rare - something I've seen only a few do. One of his criticisms is that, at times, biologists have gotten sloppy with their data, using the excuse, "This is true because - evolution." Another criticism I found very interesting comes from Ana Soto that biologists are no longer biologists. They're just statisticians (my paraphrase). None of these people are attacking evolution, but some of what they say does reflect on the way LUCA is inferred.
[EDIT] Maybe I read you wrong, but you seem to be taking the inferences that organisms are connected through inheritance as given - that since changes in allele frequency are true, then it follows that inheritance must be true. I don't accept that. Let me put it this way. If you believe no organisms remain today from parallel biogenesis events, then I take that to mean you would know how to identify one if you saw it. So, describe to me how organisms coming from distinct biogenesis events would be identified in a scientifically rigorous manner.
All of what you have said is possible. But possible is not proof. It's just supposition. Unless it can be established that origin events were only millions of years apart (or probabilities can be affixed to them) - unless it can be established that events happening closer together is highly unlikely - this is all supposition.
In answering this, I'll first say that I'm not really interested in biology per se. Never have been. I took a biology class in high school and hated it. As such, my only interest in this topic is cases where theories from the field of biology intersect with my theology. Dinosaurs and birds, mammals and whales, those have no bearing on my theology so I don't spend any time on them.
I will say the most convincing argument I've seen for related species is ERVs. So, if those two examples don't involve ERVs, I'd not feel any compulsion to accept them. We'd also have to discuss the whole concept of species to be sure we're clear on it. Even then, it's not like I haven't considered an answer to ERVs, but that answer would again go back to the issue of parallel origins.
I once asked a biologist why biology is so stubbornly set on LUCA given it's willingness to admit multiple origins is very possible (even if they think they didn't survive). He gave me an answer about its affect on current research - even current medical research. However, given that similarity obviously exists whether or not LUCA is true, I didn't find the answer very compelling.
no worries I didn't think you were, I thought at worst you might not know it :> Just wanted to clarify to avoid us talking past each other.
hmmm can't comment on the slopiness, as mentioned before there certainly has been with some things wolf packs, komdo dragon venom and such where someone got an idea and wasn't tested. But I think where science is good is where and when it tests and retests things. Definetly needs to do that more, especialy the older the ideas the more they need to be rechecked.
Sorry if I get you wrong here :> but on the similarities, there are things we can check. Again it's not just where they are similar it's where they are different, and such. Take squid and humans. We can narrow down when our lines diverged by the comperisons of both the fossil record and DNA and such. What genes we share, wich ones we don't. They some of the basic genes for certain things that all multicelular animals do, and I would assume many of those are ones tied to being multicellular, wich would put least them splitting off after multicellular life appeared. If all multicellular animals have similar genes and such that would imply it also.
Again you could use the, "Same designer same design argument." but when something is nearly 1-1.1 comparison it falls down because you will see that while one structure is analogous to another one they arn't the same. Again back to squid and humans, they use some of the same genes, but the paths are different and results are different.
another one is snake venom and platypus venom, they have similar results and effects, but the liniege is different, if I remember right platypus venom evolved from immune system, where as snake is more circulitory and such. So where species arn't closly related from way back when Linnaeus first put it together, with some tweaks like I mentioned where species look related, but are distantly. but we don't find feathers on crocodiles, we don't find other similar chimera or least true ones. The mammals that lay egs are the ones closest to reptiles and such and on, and on.
Problem with ERV's is they only last a short time, they are useful for telling closly related, like they help us with humans and other apes, but once you get back toawards monkeys they start to break down. The issue is since ERV's generally arn't coding, there is no reason for them to be preserved, so the base pairs might change on their own, another ERV might take their place, you get a sequence flip, gene duplication in it's place and many other things.
Where I think the strongest evidence for LUCA is would probably be within the genetics and like I said those similarities and differences, and where they line up.
You havn't really given a good explanation for why these things all lineup. Humans have genes for things that make no sense without our ancestors from other apes and such. one of them is a gene for a protein in the muscles of our jaws that would make speaking impossible as we do, but other apes have.
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