Alan doesn’t believe that there are any other proposed explanations to rival ‘evolutionary theory’. At least none that so effectively account for the facts.
It is often said that there is no single theory of evolution, there are a group of mutually consistent theories. Be that as it may, I think we all understand the point Alan is making.
Evolution is a process whereby life has somehow emerged from a lifeless physical world and there is no overall teleology involved in its diversification. The reproductive processes produce a natural variety of forms which can take advantage of previously unoccupied niches. The basic sequence of events from primal to present are: lifeless minerals, water systems and gaseous atmosphere, followed by the arrival of simple prokaryote life forms, followed by multicellular organisms. Life is solely the product of physical and chemical processes acting on lifeless matter.
In this view life is nothing special, it just occurred because physical matter chanced to arrange itself in a particular way. And consciousness is just a by product of life.
But I suggest that there is an alternative way in which life as we perceive it could have come about.
Arthur Zajonc in the book Catching the Light: The Entwined History of Light and Mind
Goethe was right. Try though we may to split light into fundamental atomic pieces, it remains whole to the end. Our very notion of what it means to be elementary is challenged. Until now we have equated smallest with most fundamental. Perhaps for light, at least, the most fundamental feature is not to be found in smallness, but rather in wholeness, its incorrigible capacity to be one and many, particle and wave, a single thing with the universe inside.
In the same way that in the above quote light is understood in its wholeness, so can life be understood as a whole. The variety of earthly life forms that have existed through time and space are individual expressions of an ever present archetypical whole. Life is one and many.
Holistic science attempts to get closer to the mystery of the dynamical emergence of the diversity of living forms within the unity of the continuously manifesting whole.
An arithmetical analogy between orthodox accounts of evolution and evolution as the unfolding expression of archetypal forms could be that the former is akin to addition while the latter is akin to division. Novel forms are an extra addition to what came before or novel forms are divided off from what already existed in potential. From the parts to the whole or from the whole to the parts. Which is it? Sense perception points to the former while the mind’s eye, perceiving with the mind, points to the latter. And Goethe was an expert at perceiving with the mind.
Instead of life emerging out of matter in an extended version of the spontaneous generation of mice from mud, it could at least be regarded as a possibility that physical organic life is a condensation or hardening of form out of a more subtle general condition which contained all physical forms in potential. This is analogous to crystals emerging out of solution. The perception of salt in sea water is dependent on the senses of the perceiver. Some forms of life have not descended as completely as others and thus retained more plasticity and because of this they are more adaptable to changes in their surroundings.
Life is and always was everywhere but it is only when it coalesces into gross material forms that it is perceptible to our everyday senses.
Convergent evolution is explicable not just by occupation of similar niches but by similar forms coalescing.
That wasn’t from the abstract, it was from the conclusion.
And I don’t disagree that already having the ability to produce dentine and enamel makes it easier to produce teeth. The example of Gastrotheca guentheri tells me that although frogs have evolved in a fairly narrow, one-sided direction, they still retain a certain plasticity.
But the fact that it has remained an amphibian for hundreds of millions of years tells me that it is far more static in form than higher animals that have changed considerably in this time.
I even have reservations in regarding these examples as contradicting Dollo’s law. Everything spirals on and the future never traces a path which is exactly the same as that traversed in the past.
But if Wiens is correct then this attribute of these frogs has laid dormant for over two hundred million years. I presume you believe that this trait has reappeared due to some unspecified chance genetic change? But that is all it is, a belief. You are welcome to believe that this trait benefits the frog and so it fortunately just re-emerges. What about all the other frogs that don’t seem to need this trait, how do they cope? And how did this species survive for so long without the need for these teeth?
Do you know why the genes required for these teeth are expressed in the precise somatic cells where they are needed? If so can you share the details?
CharlieM,
Teeth and the genes for them are not one-to-one. I’m sure you have heard of HOX genes and how regulatory genes switch other genes on and off to oversee development in the embryo. Frogs have retained teeth on the upper jaw so the genes for teeth can be retained and mutations in the regulatory system can suppress the growth of teeth. Selection will favour teeth loss in certain niches and not in others. I presume frogs who have evolved a new bottom set have some differences in diet or method of getting food that caused them to reacquire teeth. I wonder if anyone has looked at niches and how frogs with and without teeth exploit them differently.
So can you tell me what controls which genes are expressed in specific cells?
It’s very strange.
Last summer, my car blew air at my face.
Then in winter, it lost that ability.
Now that summer is here, my car has regained the ability to blow air in my face.
Sez Charlie:
As others have noted, the switches and levers you seek are the HOX genes.
I was merely making fun of the ridiculousness of your “in the very position they needed to be” request.
CharlieM,
I can’t. Most of the detailed work was done on fruitflies.
It is indeed.
Our visual system is a marvel in itself, consisting of the eyeballs and optic nerves connecting them to the brain. But just think of all the accompanying features and processes that go along with the organs themselves. The bone formation required to accommodate them and to allow for the passage of nerves and blood vessels. The blood vessels to nourish them and remove waste. As you say the gaps in the skin and the formation of eyelids for protection (anyone who has knitted a cardigan will know what is involved in constructing the button holes and that is infinitely more simple than what is required to form the dermis around the eyes). The formation of tear ducts and lacrimal glands that allows aqueous fluid to wash over the eyes and then to drain away. The composition of the fluid itself. The six extraocular muscles, ligaments and accompanying nerves required to move each eyeball as required and the various muscles, ligaments and nerves attached to the eyelids and surrounding areas. The eyelashes and eyebrows protecting the eyes.
It is truly amazing to think of all the coordinated processes that go into the development and functioning of the visual systems of higher animals. Just think of all the cellular activity that was and is going on to produce the host of protein complexes vital for the correct development and functioning of this one system among many other such systems.
CharlieM,
And yet this process with the result of a pair of fully-functioning eyes together with the brain and nervous system has developed from one cell, countless times.
It’s almost as if we don’t get to hear about the failures!
Yes Hox genes are quite remarkable. Their arrangement conforms to the arrangement of the body reflecting an anterior to posterior positional order. The whole reflected in the parts. This is easier to see in fruit flies as opposed to mammals. This is understandable as fruit flies display overall segmentation while in adult mammals the obvious segmentation is confined to the vertebrae. And the greater complexity of the mammal form is reflected in the more complex system of Hox genes. It might be relatively easy to induce limbs to grow out of a head segment in drosophila but as far as I’m aware this has never been done in an organism such as a mouse.
Here is a reference to a paper which give us an idea of the complexities involved:
The complexities involved should not be overlooked.
Development is not just a case of expressing genes in the right place at the right time. All the somatic cells of the developing frog have the potential to produce the materials needed to form teeth. Selective suppression of gene expression is also an important factor.
Compared to frogs, human teeth are more varied in that their form is geared to specific functions. How this variety of form is achieved remains a mystery to researchers as far as I’m aware.
Wikepedia has this to say:
This is not so much of a mystery from the point of view of their development being governed by the cooperation of polar opposite ‘forces’ as I have advocated previously. Substance production from below and form building from above.
Doesn’t matter. The explanation is quite portable: precursor cells of the upper and lower mandible express a similar repertoire of transcription factors (such as HOX genes) during development. Little wonder teeth re-emerge in the correct place.
… because all amphibians look the same to me 🙄.
I’m not seeking switches and levers. I am trying to clarify (mainly for myself) what it takes for features like these to become manifest. And the answer involves many coordinated processes working together.
Ask yourself what it took for that function to be possible in your car and then massively ramp up the complexity and coordinated effort required for individual features in living organisms such as the frog.
If only it was as simple as, “the Hox genes did it”.
from here
This is an article on mammalian Hox genes
They talk about combinatorial complexes of protein codes orchestrating morphogenesis. It takes a great deal of logistics to ensure that the right amount of material is available at the right place at the right time to maintain the viabilty of a developing organism. There is no conducting Hox gene or Hox genes. They may be very important players, but nevertheless they are embedded within the orchestra.
OMagain,
Confession, I was hoping Charlie would bite and I could respond with the apocryphal riposte by J S Haldane to the evolution critic who collared him after a lecture saying something along the lines of “Even allowing for billion years of evolution, how can you get from a single cell to a complicated human body, with complicated structures and organs, blood vessels and pumps…”
Haldane: But madam, you did it yourself. And it only took you nine months.
(pinched from Dawkins as recounted in The Greatest Show on Earth)
To take the most basic example, multiple castings can be produced from a single mould.
Life is all about maintaining the balance between constructive and destructive forces. These are necessary polar opposites. What is considered to be failure at one level leads to success at a higher level.
CharlieM, That story from Haldane gives the title to chapter 8; You did it yourself in nine months.Dawkins admits (2009) it was a bit of a copout as the same question can be shifted to how did the development system that orchestrates the process evolve.
But he attempts an answer that he acknowledges is partial which I would summarise as local rules and emergence.
What is it that stimulates their expression here yet suppresses their expression everywhere else?
We recognise them as amphibians because of shared essential features. I can’t speak for you, but toads and newts look different to me and I still recognise them as amphibians.
Positional information. Did you ever read Sean B. Carroll’s book “Endless Forms Most Beautiful” ? It’s an oldie, but I liked reading it.
Ah, yes. ” They all look the same to me”. I remember how well that argument went when classifying snakes.
Do you recognize this one?
From these indistinct visual images it isn’t easy to precisely distinguish what they are. But if the average intelligent person was to have access to each individual organism displayed in these images, to be able to examine them in their development in their natural habitat, most if not everyone would be able to say, “yes this is an amphibian” as the case may be. Thinking gives us access to information that senses alone cannot get. Thinking is an inner sense which completes our outer senses such as eyesight.
Yes, the whole(evolution) reflected in the parts (individual development).
All one needs do is accept the possibility that evolution is a process whereby matter is arranged to the point where it becomes self-aware, then things start to make sense. The evolution of consciousness is key.
I’ve only read excerpts, never the whole book.
No but I know of something similar. I used to keep slow worms as pets when I was a kid. I remember one that I called ‘Oscar’. I used to make a hole in a chickens egg big enough for its head and it would put its head through the hole and eat the contents.
Here is a photo of one:
Alas, Charlie, that was not a slow worm. The picture I posted depicted a Caecilian, which is (you probably guesssed it), an amphibian.
Sorry to have trapped you like that, but this was the most efficient way to make you realize that amphibians have diversified beyond the point where you can recognize all members by their “shared essential features”. You really should stop using the argument that non-mammalian groups are “static”. They are not. That’s just your lack of appreciation of the tremendous diversity within those groups.
I did wonder, on glancing at the photo, which was head and which was tail as both ends are blunt and there are no visible eyes. I guessed flower-pot snake. Nuls points for me!
Hey, I recognize that! It’s a glass snake, which is not a snake at all, but rather a legless lizard.
You didn’t trap me. I did not recognise it but I was able to google it from the file name so I knew it was an amphibian, no guessing required. And like I said the image I provided was similar in that it looks like a snake but is actually a lizard. It too is not what it seems.
I have never denied that amphibians are extremely diverse. My point is that they have remained at a stage of evolution passed through by the ancestors of higher vertebrates mammals and birds earlier in their evolution. It is in that sense that their further evolution has stalled.
The clue was in the file name, Oscaecilia_ochrocephala
CharlieM,
That would have been cheating!
That’s quite the admission. So the shared characteristic, in this case, is having an amphibians’ taxonomic designation. That‘s how Charlie could tell.
Err, no, it’s a tree, not a ladder.
It’s a slow worm, scientific name, Anguis fragilis, found in Europe. I think that ‘glass snake’ would be what they are called in the U.S. I know there are legless lizards there too but I don’t know if that particular species exists there.
Not if you had admitted that you did not recognise it from the photo, as I did 🙂 Although I guessed right away that it must have been some sort of amphibian.
Well the experts have designated it as an amphibian, no doubt through morphology and life cycle. Having faith in the experts I don’t believe they could have made such a basic error as misclassifying it from the available knowledge.
It makes no difference. They remain on the lower branches.
A terrestrial mammal reaches maturity by passing through a stage where it exists wholly submersed in fluid. Once freed from this ‘water’ existence it has no need to return. Amphibians in general are obliged to return to the water to breed.
CharlieM,
Last I heard, amphibians included frogs and salamanders, but not lizards. Unless you folks are going all cladistic on us, in which case I get to call us all amphibians.
I would be happy to call myself an amphibian plus plus. If I traced my family tree back far enough I’m sure I’ll have had amphibian ancestry, not to mention fish ancestry.
You did a bit. You claimed amphibians were “static in form” and that this was supported by the fact that as a group they were easily recognizable. As I see it, the existence of a group that is so derived that you need to rely on expert knowledge to identify it as an amphibian strongly contradicts your claim.
Where in our evolution did we lose our extendible tongue, our leaping hind legs and our toxic glands?
Oh, I forgot. They don’t count. Only solving sudokus and such counts.
No, Jock is right. There is no such thing as “lower branches” in the sense you mean, because all extant organisms are at the tips. Hence none of the branches takes a priviliged position.
You want causal explanations? That’s quite curious. I prefer them too, which is why your alternative is so unsatisfactory.
By ‘static in form’ I mean that they have stabilised at a level where they are on the cusp of a terrestrial existence but they never reach beyond this transitional stage. I am not talking about ‘form’ in the way you think I am. Not as might be seen in a still photo. Amphibians are dependent on an external watery environment to further their existence. I never claimed that they are necessarily easily recognisable.
But if you want to stick to forms as portrayed in pictures, then frogs, toads, salamanders, newts and caecilians have all existed in recognisable form since the Jurassic and beyond.
I don’t need expert knowledge to determine if an organism is an amphibian, I just need to observe it through a complete life cycle. But that is beside the point. I am not talking about picking out the suspect amphibian from a line up of various shady looking vertebrates. I am talking about the objective attributes possessed by the organism which qualify it for inclusion in amphibians.
Extendible tongue, our leaping hind legs and our toxic glands are not defining features of amphibia. For example there are some frogs that do not have tongues and caecilians certainly don’t have leaping hind legs.
It wouldn’t be far off the mark to say that amphibians had their day at one time but now they are well into their old age.
From Science Daily
Now endothermic amniotes hold these positions.
In a tropical rainforest do you not think that the branches in the canopy have a privileged position?
No. I’m looking to see if a linear causal explanation is in any way possible.
Perhaps I think you are talking about “form” in the way that I think you are talking about it because of statements like these:
This part sure sounded like you tried to group them by similar morphology.
Not morphology then, very well. What are those non-morphological objective attributes?
Even if I were to accept that this metaphor makes sense in this context, then extant amphibians do not get relegated to the “lower branches”, but are on equal footing with “higher animals” (whatever you imagine those to be).
ETA: clarity
Morphology is important but on its own it is not always enough to classify the organism.
Not morphology alone.
Amphibian eggs do not possess anything like an amniotic barrier and so they need to develop in a liquid environment to prevent them from drying out. They go through a metamorphosis from an aquatic existence to a terrestrial existence.
In comparison with mammals their development is externalised. Mammals have internalised this process of metamorphosis by means of which they are less dependent on the external environment. A process of emancipation.
It all depends on whether or not you think of self consciousness, rational thought, planet-wide communication and travel, extensive communicable knowledge and inventiveness as consequential. Would you put the smartest bull frog on a par with Newton or Constantine or Hitler?
What exactly do you mean by “linear causal explanation”?
An interesting feature of Hox genes is the duplication at the base of the vertebrates, plus several other duplications in various subclades. All invertebrates have 1 cluster, but there is a lot of variation in chordates which is likely to have a fair bit to do with the morphological expression within the group. Within each broad clade there is significant conservation. Tunicates have 0 clusters (not sure how they control larval end-to-end expression), lancelets 1, hagfish etc >3, sharks/rays 4, bony fish 7-8, coelacanths 4, tetrapods (that’s us) also 4.
Invertebrates managed to generate a lot of diversity with their poxy single cluster, of course. But some of the re-purposing of these duplicates, permitted by the fact of duplication, has a vital role in us. Proponents of a ‘forward-looking’, anticipatory evolutionary theory should consider how this relic of invertebrate patterning was made available historically in order to also provide the patterning of (for example) the cranial ridge, or the 4-limbed form which allows certain descendants to get up on their hind limbs and oppose those Xbox-ready thumbs.
So you classify amphibians by their lack of amniotic membrane and metamorphosis during development. Are you sure you want to classify amphibians this way? By this definition, mosquitos are bona fide amphibians.
Tip: Don’t classify organisms by their lack of characters we happen to have.
This is all gobbledegook. It sounds like you want to make a lot of the fact that amniotes have adapted to a fully terrestrial life style (exceptions abound), but none of this establishes that amphibians are “static in form”. If anything, having metamorphosis is the absolute opposite of being “static in form”.
This is your usual mantra. No, it does not depend on that. I do value those things, but that doesn’t turn evolution into a teleological process.
Nature cares exactly as much about amphibians as about rational self conscious Charlie. Tough beans!
And there are always exceptions. The common coqui Eleutherodactylus coqui bypasses the tadpole stage, completing its metamorphosis within the egg and is therefore capable of terrestrial breeding.