It’s funny, you’re the second person to tell me all that recently. Thanks, and you’re right, of course, but I have an unhealthy compulsion to not leave false claims hanging out in public where unknowing passers-by might run into them unprepared. I’ll do my best to work on it. I’ve got a lot of free time on my hands at the moment and this is fun, easy, and passes that time, but I can assure you than when I’m snowed under again I’ll be better at prioritising my time. I don’t plan on letting my research suffer for the sake of arguments on the internet, for example.
@evograd - Please don’t take what I said as chastisement. I’ve fallen down the hole several times myself when it comes to science/religion and politics/policy as well. 
But I do want to take the time to say that your pattern of marshaling evidence and staying on topic and away from dismissive insults is truly impressive. Well done and your skills in rhetoric and scientific argumentation will serve you very well in your career!
Both the above claims are made by you. You started off with a mechanism. Now that you are challenged, you are claiming it’s just a descriptor without involving a mechanism. I have no problem with the second modified claim.
Except that the simplified claim is not accurate. Accuracy is important for me…(probably one of the reasons I don’t read pop science…)
What do you think it was?
I have never seen an explanation of how convergence works at the molecular level.
Hi Nathan,
How do you think the fact about glut 1 effects you claims about vitamin C?
Thanks again, I really do appreciate that 
I know it wasn’t meant as a chastisement, just good advice, and it is that. While I enjoy these kind of debate forums, I know I invest way too much time in them while practically “coasting” in my research. A lot of this time would be much better spent focusing on that explicitly or generally improving my knowledge of my field (my backlog of papers and books is painful to think about for too long) or of relevant methods (I want to learn Python properly soon, for example). This academic year I want to take my approach to my research to the next level, and I don’t mind sacrificing the more trivial or pointless arguments on the internet to do that.
Read exactly what I said in the first quote. I said it would be explained as convergence. As in “the observation other mammals have a similar mechanism of vitamin C efficiency doesn’t necessarily indicate shared ancestry (as you wondered aloud), convergent evolution would easily work too.”
Perhaps I was unclear in my words, but I know exactly what I meant. You’ll just have to trust me that I haven’t changed my mind halfway through this thread. I certainly never indicated that merely saying “it was convergent evolution” actually expains the precise dynamics of the independent evolutions of the trait rather than its distribution throughout the phylogeny.
That’s great, but you should tone down criticisms of popsci writers. If they say something “innaccurate” in your eyes, consider that they’re just trying to keep it simple for a lay audience rather than being ignorant or intentionally being deceitful.
That we need to get vitamin C from our diets since we can’t produce our own. That’s about it. The article was about our need to consume micronutrients, not an in-depth discussion of the relative selective forces involved in the different molecular pathways at the origin of this trait.
1 Like
Do you mean explanations of examples of molecular convergence (e.g. in Prestin), or molecular explanations of convergent evolution (e.g. in gross morphology).
Lets start here. How did an eye evolve more then once?
You made a specific claim about a mechanism…
I don’t see whats the point of denying what you claimed.
why “glitches” in human design should be an important scientific topic is beyond me… How exactly does one scientifically define a glitch? Even the topic is irrelevant to science.
People buy “pop science” books to learn real facts… so there is nothing wrong in expecting the science to be factually correct. If he can’t do it, then don’t … But end of the day, people are buying a product whose premise is scientific accuracy…
I did notice a claim that this need for micro nutrients can be explained by our diet during early human history in Africa.
It seems that was the main point. For example, shifting from a vegetarian diet to that of an omnivore, allowed is to loose the ability to directly access the B12 produced by bacteria in our gut.
Wonder how that would stand against a fact check.
Good distinction.
1 Like
The reason I asked the question is because explanations of examples of molecular convergence, or molecular explanations of convergent evolution are very different things. The first is easier, and is more specific to convergent evolution. The second, which is the one you’ve decided to ask about, is easy to give a superficial answer regarding the convergence itself, but harder to answer literally - molecular detail of the origins of a gross morphology.
I’ll try to be a bit less cryptic. You asked for an explaination of the “convergence” of the trait. The simple answer is that convergence in gross morphology is usually pretty simple: “it evolved once in one lineage, and also in another lineage”. Having “molecular” into the question turns the question mostly into one about molecular evolution of morphology in general, although I guess it could include the subject of deep homology as well.
I still don’t feel like I’m getting my point across, so I’ll keep trying. Saying “explain in molecular detail how trait X evolved twice”, is little different from saying “explain in molecular detail how trait X evolved in clade A. Then explain in molecular detail how trait X evolved in clade B”. Without bringing in deep homology etc, that’s all it is. Convergent evolution isn’t some special flavour with its own molecular dynamics - it’s just the process multiple times independently. Again, if what you’re getting at it deep homology and the shared starting points of traits like eyes, let me know.
1 Like
Thank you. I think you have given a very honest answer. Convergent evolution is a point where universal common descent by mutational modification appears to break down. We not only appear to see incredible innovation but this innovation is not following an inheritance pattern.
1 Like
I didn’t make any claim about a specific mechanism for the evolution of our increased vitamin C efficiency. I suggested some plausible broad strokes about the order of events, but that’s about it.
I said:
- Produce vitamin C => coexpress stomatin and Glut4, not Glut1 in erythrocytes.
- Don’t produce vitamin C => coexpress stomain and Glut1, not Glut4 in erythrocytes
but this is just a paraphrasing of the paper you referenced. The state of affairs. The “explaination” I offered was that the regulation of Glut4 and Glut1 changed - that’s trivially true. I’m on the left side of the street, I want to get to the right side, how do I get there? I travel there. That’s the equivalent of the “explanation” I claimed. Afterwards, I said I would be interested in learning about the specifics of how this happened, and spitballed about enhancer gain/loss.
You’d have to ask @NLENTS for the specific definition he uses, but I think most of us interpret it to mean “imperfection”, or “where something got broken”. Our inability to synthesise our own vitamin C and the GULO pseudogene fits pretty nicely. Not sure what you mean about the topic being “irrelevant to science”. The definition and usage of the word “glitch”? Maybe. The content of his article? Not at all.
You’re being a bit absurd, I think. You must know as well as I do that popular science is a simplified version of actual science. Of course a good author’s intention is to educate their audience with real facts, but it’s impossible to avoid some simplifications along the way without turning off most of the readers.
Have at it.
Nathan fleshed his thoughts out a bit more here:
Exactly how this glitch in our gastrointestinal functioning came about is largely a mystery. Most primates are herbivorous and indeed all of our fellow apes subsist on a fully or mostly plant-based diet. It is therefore likely that we descend from a long line of vegetarians. During the millions of years our ancestors thrived on plants, they surely were able to capture the vitamin B12 that was being made by bacteria in their guts, or else they wouldn’t have survived. Once our forebears began scavenging meat and bone marrow, they found themselves with a steady supply of dietary vitamin B12, which then grew in abundance when we began to hunt. It must have been during this meat-eating stage in our evolution that we began to absorb B12 in the small intestine instead of the large one. We are now stuck with this odd arrangement, making humans, at least in this very narrow sense, obligate carnivores.
http://blogs.discovermagazine.com/crux/2018/08/13/vitamin-b12-essential/#.W4_zoC2Q2u5
Not sure what you mean here. Can you expand on it?
Based on universal common descent by mutational variation I would expect complex features to appear once and then follow an inheritance pattern.
The multiple appearance of features (convergent evolution) not following an inheritance pattern would appear to falsify the original theory.
Except that both of us don’t know whether that is all that happened. Glut1 is just one thing that emerged from a 15minute search in Google scholar. There could be more.
So let’s just leave it at “unknown causes”. I have mentioned this before.
The analogy could as easily be you in two places at once.
I intend to… not today though… the important questions would be-
Till what point were we or our ancestral species vegetarians.?
At what point in which species does the change to becoming omnivores happen?
Does this species or a subsequent species show the Inability to absorb B12?
Which bacteria in the human gut produces B12? And when did they colonise the human body?
It would be an interesting study. If I can find the details. If you find anything,please share.
What about “universal common descent by mutational variation” prohibits features arising multiple times, and then after that following an “inheritance pattern”?
You brought up the Glut4/Glut1 reference, I said it’s findings were compatible with convergence. That’s it. This is so simple to understand…
That completely changes the nature of the analogy, don’t even go there.
1 Like
Is it… when all you mean is that it’s findings cannot be attributed to common descent?
Why not? It seems an appropriate analogy to me…