Nathan Lents: Why Human Have Such a Needy Diet

Of what we know of inheritance we observe genes and features are passed on from generation to generation. Now you’re trying to claim that not only have genes and features been lost but they are been gained (convergent evolution).

This is an extraordinary claim as part of an inheritance pattern. What evidence backs up gene and feature gain as a claim that happens during long time intervals of inheritance.

My sense is that the anomaly was spotted given a name and then assumed to be compatible with the theory.

Because then the analogy would no longer be about “having an inefficient vitamin C system and getting an efficient one”. If you really want to bring in convergence for some reason you should want to change it to “both me and my friend are on the left side of the street, how do we get there? We travel there individually”.

Nope… it would have to be two yous… after all its the same system appearing in both humans and guinea pigs!..

The appearance of new traits is already a given, as per your words:

You’re saying that UCD with variation from mutations can do that once, but never twice. Why not?

Your sense is wrong. You make it sounds as though we were all happy, going along with our nice neat story of evolution and inheritance and then suddenly someone noticed this horrible analogy, and everyone scrambled to give it a name to make it compatible with the existing theory. Convergence has been known about from the very beginning of the theory of evolution - it’s kind of hard not to notice that both bats and birds have wings, for example. The vast majority of the time convergence is actually easy to spot because it actually doesn’t give the impression of common ancestry. Take bird and bat wings again, for example. It’s immediately apparent that while they’re (very superficially) similar, they’re actually very different. This is because convergence (by definition) starts from at least somewhat different starting points, and because there is a major element of chance in variation, and because selection pressures can be quite different. Birds and bats superfically might be mistaken as close relatives because of their wings, but it doesn’t take much effort to realise that they’re very different. Ergo, their wings evolved independently. If the animal kingdom was just replete with examples of “perfect convergence”, more closely resembling pathworks of different specific morphological characters with no discernable pattern (like horses with shark teeth, primates with bird wings, fish with kangaroo pouches), you might be onto something. But the world doesn’t look like that at all, does it?

Sigh. You really don’t understand the analogy at all. Maybe that’s why you objected earlier. In the analogy, the 2 different streets are the different systems, think of me as a marker for which system is posessed by the lineage in question. In the analogy including convergence, let’s say I’m the human, my friend is the guinea pig. We both start off at the left side of street - producing vitamin C, coexpressing stomatin and Glut4, not Glut1 in erythrocytes. We want to get to the right side of the street - not producing vitamin C, coexpressing stomatin and Glut1, not Glut4 in erthyrocytes. How do we get there? By travelling across the road - changing the regulation of the Glut1 and Glut4.

That’s all I was saying, and that’s all the analogy is saying. Do you get it now?

That’s just not accurate. @Ashwin_s there are ways to test if it’s consistent or not. You can’t just assert it.

Thanks very much @evograd !! I appreciate your answers and explanations. The wiki article, linked, is helpful too.


@evograd never mentioned any particular tests… are you aware of any tests in this particular case?

Yes. He is explaining it to you with words but I wonder if math might help.

I am skeptical that mutation alone can form the functional information required for new features. Mutation breaking down a functional sequence makes sense. Forming one does not make any sense to me.

So saying it happened twice or more does not make sense.

It’s definitely worth a shot.

Nathan, thanks for stopping by and adding expert commentary. I enjoy your book “Human Errors”. Insight from your book, actually lowered my fear and anxiety about having to go to the eye doctor and be checked for age related eye problems. Last month I went to my ophthalmologist for my regular annual eye examine. This year he took a high resolution picture of my retinas with micron resolution. And he found tiny holes in my retina. I asked him what caused them and he said that the retina is behind blood vessels that some times leak fluid. In the past these holes could grow into a full retina detachment but now he could easily tack the retina down using a laser. So I had the laser surgery the next day and I assume it is resolved. By reading your book, I realized that it was a design problem made hundred of millions of years ago. I felt very fortunate to live in a place and time where I could go for a exam, find a million years old design problem, and then fix it.
So writing popular science books can improve lives. I was less apprehensive and less fearful about what is now becoming routine fixing of our body’s design flaws.


Hi Nathan, How do you think the fact about glut 1 effects you claims about vitamin C?

I think it shows how mutations and selective forces often lead to the evolution of work-arounds to various challenges. In this case, the inability to synthesize vitamin C placed a powerful limit on an otherwise very successful lineage. Given the long time periods we’re talking about, it was inevitable that mutations that mitigate that limit would emerge. When they did emerge, those individuals had a huge advantage over others and so the workaround spread quickly in future generations. Not only is that not surprising, it is expected.


You seem to be assuming that what you call a “complex feature” is highly unlikely, and thus shouldn’t evolve multiple times. But maybe that “complex feature” is very likely to evolve.

Not with making random changes to a sequence. How does this do anything but break it down?

Great story! What a perfect example of how our species has used one adaptation (big brains) to compensate for poor design elsewhere! Besides the blind spot, retinal detachment is the other big problem caused by the inverted arrangement of the photoreceptor cells in the vertebrate retina. If you don’t mind, let’s talk about this over on my thread about the evolution of the eye that opens next week. :slight_smile:


You’re welcome to believe that, but you said it falsifies the theory. I thought you meant “it’s incompatible with the theory as it’s understood by scientists”, but you actually meant “I think evolution can’t possibly explain it”. Do I have it right?

And that’s why you’re the author :slight_smile: Great succint explanation.


This is the wrong way to look at evolution, just as “making a sequence of steering wheel motions” is the wrong way to look at driving from here to Los Angeles.


Since you obviously don’t know which mutations are required. You are not speaking from any evidence that the required mutations would inevitably arise. Since you mentioned time, do you have any idea what timelines you are talking about. As in at what point these mutations for glut 1 emerged in guinea pigs and humans?
Have you heard about the omnigenic hypothesis?