Below is an image of the developmental path from human conception to adult in comparison with evolutionary path from prokaryote to human.
Unlike Haeckel’s biogenetic law with its focus on physical forms, the comparison above also concerns activity, lifestyle and behaviour. Comparative stages may be vastly different in detail, but the similarity of general lifestyles and consecutive stages are there to be observed.
Human life begins in an aquatic environment. Toddlers gradually learn to walk upright from a previous state of crawling and moving around on all fours. The brains of children develop through daily interactions and experiences. This brain development accompanies the child’s increasing ability to achieve complex manipulation skills using hands that have been released from the task of providing support and locomotion, and also the practice of producing sounds using the various muscles of the mouth. Well developed brains allow for rational thinking and the creative use of language.
Human minds have brought about technological advances which have allowed human activities to engulf the planet. Signs of intelligent human activity are evident a good distance beyond the earth spreading ever further out into space.
The various forms of extant animals and all other life forms have evolved as an integral component of the living earth and the whole forms a dynamic system.
The various animal forms should be studied in the context of the complete system in both time and space. Conditions would have been very different prior to the terrestrial colonization of earthly life In all probability none of the present aquatic animals would bear any resemblance to the aquatic ancestors of humans and other higher vertebrates save that at some stage they all require an aquatic environment for their continued existence.
From a point of view which regards physical organisms as the individual expressions of overarching general forms, the evolution of cetaceans need not have involved moving to the land only to return to the water at a later time. They may have reached the mammalian stage of evolution but in a way that was suitable for an aquatic lifestyle. They adopted the archetypal mammalian form in a way that suited an animal living in an aquatic environment and there would be no need to posit a terrestrial stage in their evolution.
It’s my belief that higher consciousness is ever present. Evolution is the process whereby higher forms of consciousness descend from the group level to the individual level. The most fully developed individual consciousness which I am aware of on earth can be found in humans but it is still rudimentary compared to the higher level group consciousness.
Plasticity is a fundamental feature of living systems at all levels from human brain development to the radiation of multicellular life. Paths are formed by branching out and becoming fixed along certain lines. It would be impossible to forecast specific paths but, nonetheless, there is a general overall direction.
Now that biological life has reached the stage where social organisms have become individually creative and rational, the all encompassing Word is reflected in single beings. This could not have come about without preparation and the evolution of earthly life is the evidence of this preparation. We, as individuals, are only able to use language and engage in rational thinking because our individual development has prepared us to do so. Likewise humanity could not arrive at the present state of culture without the evolutionary preparation in its entirety.
Focussing in at the lower level gives a picture of ruthless competition, of nature “red in tooth and claw”. But from a higher vantage point life benefits from this apparent brutality. For instance if a sparrowhawk makes regular hunting visits to a suitable habitat in your neighbourhood it signifies that this environment supports a healthy songbird population. In the case of the continued evolution of physical forms, survival of the breeding population is more important than any individual’s survival. In the evolution of consciousness the individual is the important unit.
I think it is a mistake to see biological evolution as a blind random groping towards an unknown and unknowable future.
No, I perfectly understand wat he is saying. It is your writing I am struggling with.
In that way birds also met their demise. You are not communicating, Charlie.
What Jock said. This is NOT the point I am trying to make.
Sure, and when humans are born they leave the amniotic fluid of the womb. You see a parallel between those two transitions, hence you conclude that, like human development, human evolution follows a path to some predetermined outcome. Everybody here gets it; it is not a very complicated argument. It’s just not that persuasive.
For the Nth time: this is a superficial resemblance that does not withstand close scrutiny. For example, the “quadruped” stage of babies/toddlers is caused by the fact that they haven’t trained their legs yet to become strong enough to support biped locomotion. This is NOT because they are recapitulating some previous evolutionary stage.
And I do not have time to go into that: it follows from the fact that many primates (with whom we share a common ancestor) have an arboreal lifestyle and from study of the morphology of extant and fossil primates.
This confused discussion is the result of your inclusion of a monkey in your figure to represent some stage of human evolution. Perhaps you should stop viewing extant animals as primitive stages of human evolution and start thinking of them as fully developed modern beings in their own right.
You’re right. I’ve not been paying enough attention to Corneel’s point. Thankyou for pointing it out. My only excuse is that because of other distractions I haven’t given myself enough time to review the ongoing conversation.
Moving on.
So I hope most of us would agree that the transitions I mentioned in both development and evolution are not trivial or superficial. Any disagreement lies in the connections between individual history and evolutionary history.
Human embryos develop tails after a few weeks of development and this is sometimes used as evidence for evolution. Should this connection be considered superficial and irrelevant?
I believe that meditating on a phrase such as “The whole reflected in the parts” and “As above, so below”, which at first would seem to be trivial sayings start to reveal deeper meaning that applies to extensive natural processes. It’s not a case of pre-emptively trying to fit observations to the phrase. Connections should not be forced. Of course this is my personal experience and I don’t ask or expert anyone to follow what I do or accept what I say. I’m just explaining my position.
I am not talking about analogous structures but analogous processes. In the transitions from tadpole to frog, prenatal humans to post natal humans and vertebrates moving from sea to land, they all require rearrangement of the circulatory system to accommodate air breathing. Obviously this needs to be achieved in specific ways to suit each organism. But these processes are equivalent in that they are transitions from one like activity to another like activity.
The likeness is in the general activities and not in specific structures. If you think about what Goethe was saying when he said, “all is leaf”, he did not mean buds looked the same as leaves.
I don’t think this is worth speculating on any further.
I didn’t rule them out, I questioned why they would be motivated to do so. I get the feeling we won’t find out any time soon.
I don’t see why it would be rude to ask someone to clarify what they are saying
Well, asking for clarification (once) would not be rude. But that is NOT what you are doing with your “So what you are saying is [insert non-sequitur here]” gambit.
Thanks for acknowledging this.
Yes.
Atavisms and embryonic vestigial structures in isolation are not taken as sufficient evidence for evolution either; they are part of a large body of supporting evidence.This is exactly what I was requesting from you: some explanation how the processes underlying this “deeper meaning” result in the resemblances (and differences!) we currently observe between evolution and development.
Heraclitus: “It is wise to hearken, not to me, but to the Word, and to confess that all things are one.” 🙂
The birds around us are extant but they bear sea creatures and reptile-like beings within their history. We also contain sea creatures and reptile like beings within our history. They are a part of us.
Heraclitus; “All the things we see when awake are death, even as all we see in slumber are sleep”
The sea creatures and reptile-like beings from which birds and humans are thought to have descended are no longer present on the earth. These long dead creatures are transformed beyond recognition in their descendants. Their cousins can still be recognized. The 242myo megachirella is easily recognizable as a lizard. A 400myo coelacanth is not very different from those of today. They have advanced little in millions of years.
My apologies.
It is irrelevant whether or not it was predetermined in some way. The fact is we can trace the path because it has already been travelled. In reality living creatures we look at today are not just what we see before us, they are an inclusive whole right back to life’s beginning.
Look at an individual frog. If you want to understand the reality of its being you cannot disregard the tadpole that it used to be even if it is no longer present at the moment you are looking at it. It is the same if you wish to understand any life form in relation to its evolutionary history.
The connection is not one of causal relationships so there is no need to speculate about what caused what. I consider it more correct to think of it as a fractal relationship in which self-similarity can be observed. The second, minute and hour hands of an analogue clock rotate in a self-similar way but there need not be any causal relationship between them. They can be separately driven by one master gear.
Why should we take it for granted that just because some extant primates are tree dwellers that human ancestors were tree dwellers? It can be argued that many primates are adept at climbing trees because they have grasping hands, they do not have grasping hands because they climb trees.
It’s not supposed to represent a monkey. It represents a fairly well advanced general primate. And it has been said that “great apes tend to be less arboreal (tree-dwelling) and more terrestrial (ground-dwelling).
All extant animals are fully developed beings in their own right. But we humans are the only beings that research and share knowledge about our place in the history of earthly life. This is a step beyond the group behaviour of other social animals. Novel behaviours such as bipedalism, flying, having an aquatic existence, are not unique to any specific species. Human culture has become extremely influential on the further evolution of earthly life and it is unique to one species.
I don’t think either of us, nor anyone else who is active here, are saints, but I was wondering who else here have you reprimanded for their apparent rudeness? 🙂
Hardly a reprimand. Being a little deaf these days and with masks an added hindrance, I often use the “so, if I understand you correctly, you said…” followed by my best guess at what I think I heard. It’s a reasonable approach to clarify a point.
But you have to listen to the reply.
Now, Megachirella actually did meet its demise; It has no living descendants. Theropod dinosaurs OTOH are still among us.
Look, you have been resisting my correction for some days now, but at some point you will need to learn tree-thinking. Many of your more obvious mistakes here are related to the fact that you have a scala naturae view of living beings.
Frogs never were tadpoles in their evolutionary history so it is not the same path. The resemblance you identify (aquatic stage) is superficial and better explained by constraints from their evolutionary history.
Among other things, it’s more parsimonious to assume that humans abandoned their arboreal life style than to assume that so many primates acquired this behaviour since divergence from our common ancestor. There are other clues as well. As said, I do not have time to cover all of those here.
Yet you use them to represent primitive stages in human evolution. I strongly advise to abandon this tack.
Thanks for the thanks 🙂
Craig Holdrege wrote:
We could apply this method to gain an understanding of mammalian tails. How do primate tails or lack thereof match the lifestyle of the animal to which they belong. Many active leaping mammals use their tails for balance. Many New World monkeys have prehensile tails which can act as a fifth limb for grasping.
The bipedal locomotion of humans has no need of a balancing tail, but they may have been useful if we were quadrupeds in the past.
CharlieM,
Gibbons?
CharlieM,
Orangutans?
True. But am I the only culprit?
As I said, I use that approach myself.
Say what?
I disagree. You, Alan, use the active listening technique, which is very specifically “So, if I understand you correctly, what you are saying is …[followed by an honest, undistorted read-back of the other person’s point.]”
Charlie is a repeat user of the “So what you are saying is…[distortion of the other person’s point]” rhetorical gambit.
These are two quite different techniques. Active listening does require listening. SWYASI avoids it. There are, however, superficial similarities, which may explain why…
DNA_Jock,
Fair enough. I don’t (sorry,Charlie) always pay close attention to everything Charlie writes. I paraphrase to get clarification.
“So, if I understand you correctly, you are offering to sleep with me”
*Loud slapping sound*
“Ah, I stand corrected.”
You are not comparing like with like. Megachirella is a genus of lizard known from a single incomplete fossil. There are many extinct genera of theropods just as there are many extinct genera of lizards.
Which obvious mistakes? Can you be a bit more specific?
Would you say that they never had tadpole-like ancestors? How can you be sure you know what their direct ancestors looked like? The fossil record is very sparse and tadpoles have cartilaginous skeletons which do not fossilize as easily as bones. They do not develop into bone until they begin to transform into frogs. The earliest tadpole fossils are fairly recent.
If I were to claim that at one time the ancestors of frogs were purely water breathing and lungs were a later novelty that would arrive in their future descendants, would you agree?
The feet of humans are suited for walking, and hands for grasping so we are well suited to getting about both on the ground and in trees. Monkeys have feet that are more hand-like and so they are more specialized for tree-dwelling. If we wished to speculate, it could be thought parsimonious to believe in an advancement from being generalists to specialists.
And to give you an example zygotes are fully functioning single celled beings equivalent to single celled protozoa, but unlike protozoa they develop further, differentiate and combine to form multi-cellular organisms.
Protozoa are very successful by remaining as single cells, mammals are very successful by evolving multicellularity.
I’m not sure what you’re asking, if anything.
Do some quadrupeds use their tails for balance? Yes, it would seem so.
If universal common descent is to be believed it is more than likely that we have quadrupedal ancestors. Of course we could have descended from some sea horse like creature that developed legs and walked out of the water as a biped. 🙂
But as Craig Holdrege wrote
So, like everyone else, I do not know precisely what our direct descendants looked like. We can speculate that we have emerged from fish-like or reptile-like, or monkey-like ancestors, but there are no fossils where we can say that, yes, we are their direct descendants.
But if all life has a universal common ancestor then it is more than likely that it would have been single cellular.
CharlieM,
I have to say this is a pretty superficial glance at reality.
https://www.nature.com/articles/s41598-018-37963-z
Charlie may be interested in this video on how humans are part virus..
That was sort of the point, wasn’t it? Megachirella and its descendants went extinct before they could diversify into higher-level taxonomic groups. Crown-group squamates and theropods did not.
To refresh your memory: you claimed theropod dinosaurs met their demise. That’s ALL of them. This is incorrect.
You do it a lot. But in this thread, you missed the fact that vertebrates are a group within animals, claimed that theropod dinosaurs went extinct, failed to appreciate that contemporary large taxonomic units must all have descended from a single ancestor species and seem to be oblivious to the fact that human foot morphology being unique among primates strongly implies it is a derived trait, not an ancestral one.
If this were really true, then that would be a real problem for YOU trying to establish a strong resemblance between developmental and evolutionary stages. Actually, I do not believe the fossil record to be quite that sparse: We have a decent picture of what early amphibians looked like and they didn’t look like tadpoles.
Sure, you are describing our shared ancestors: Our lineages split after lungs evolved. No tadpole stage in human development though.
LOL. I absolutely *love* how you clearly imagine all protozoans to be featureless balls. Very well, so show me a single protozoan that resembles a human zygote.
My impression is that you accept universal common descent only because of its parallel with embryonic development. However, whenever we make inferences based on common ancestry, you start complaining about it being “speculation” and how we don’t know precisely what our direct ancestors look like.
So tell us: do you really believe in the common ancestry of all vertebrates? How about all cellular life? Or do you believe such claims to be unjustified?
All human knowledge is superficial compared to reality, 🙂
Nice and basic, just as I like it. 🙂
Of course more than just having ERVs in our makeup, physically we are a colony of somatic cells, bacteria and viruses.
You talk about the descendants of Megachirella. What did they look like? How would we know? The caelocanth was thought to have been extincts until a living specimen was found. Nobody has a clear idea of the early evolution of squamates. How do you know that Megachirella did not lie within the crown group. It’s all speculation.
That depends on how we each view death. One line of Wordsworth’s poem, “My Heart Leaps Up”, states, “The Child is father of the Man”. When viewed in this way we could say that the child meets its demise on becoming an adult. Death is not an extinction it is a change. As St. paul said, “I die daily”.
There is nothing wrong in believing that birds are theropods in a changed form. Most people would have a separate mental picture of a thropod from their mental picture of a bird. Whether we call those wonderful creatures which see daily birds or theropod dinosaurs is just human convention. Birds have their inner dinosaurs, as do they (birds), dinosaurs, and we humans, all have our inner fish.
I have always thought that vertebrates are a group within animals.
Those theropod populations that left no descendants did go extinct. And the ones that are thought to have produced birds are no longer with us. They all died millions of years ago. Would you recognise as the same species, any of the theropods that are said to have given rise to the birds and any single group of extant birds? What happens to the original “species” after they have spawned novel “species”?
(I prefer to think of the nodes as breeding populations rather than species which is not easily defined.)
And fossil primates don’t look like blastulas but we know that they would have gone through a blastula stage.
What do the experts know for sure about the ancestors of frogs?
I think I see the problem in communication here. You are picturing tadpoles based on their physical appearance and I am looking at tadpoles more as processes in the path to becoming an adult frog. When I see an equivalence between tadpoles and human development I am comparing lifestyles, behaviours and environmental conditions more than physical appearance. If I was to go on physical appearance alone I would probably say that tadpoles mostly resemble human sperm.
There you go again focusing on physical details. 🙂 Neither zygotes nor protozoans I would say are featureless balls. But they do have in common that they are both single celled creatures and if they do share a common ancestor it would most probably have been a single celled creature too. Extant protozoans are very diverse but they have evolved to be so without becoming multicellular. Multicellularity is a novel feature which has not been taken up by the protozoans in our environment. They maintain a very successful existence while remaining at the single cell stage. Most of the life forms we see around us have made a success of moving beyond the single cell stage.
It’s not a complaint, it’s an observation. Can you show my a picture of a fossil of one of our direct ancestors?
So tell us: do you really believe in the common ancestry of all vertebrates? How about all cellular life? Or do you believe such claims to be unjustified?
They are not unjustified.
It is just very difficult to untangle the separate lines of descent. Mosaic evolution, lateral gene transfer, convergent evolution, sparsity of fossils, all contribute to confounding the picture of past evolution. We are on a much more firm footing with generalities than specifics.
What do the descendants of Jurassic coelacanths look like? How would we know? If you can’t possibly know then why are you so sure that Latimeria species are, in fact, coelacanths?
In that case I propose that you send Dr. Simões a letter telling him that he was just “speculating” when he concluded that Megachirella was a stem-squamate. I am sure that your devastating arguments will compel him to retract his Nature paper.
If you decide NOT to pursue this approach, I would like you to reconsider your claim that paleontologists are just speculating.
Well, if you define “death” as “becoming an adult”, then sure you are absolutely right. Good point.
They persist as that novel species (the official term is chronospecies). The initial species did not go extinct. That term is reserved for lineages that left no descendants.
You see Charlie, most people use words with an agreed upon meaning so they are able to communicate. This is generally preferred over, for example, having a private vocabulary where “death” means “becoming an adult”.
That might be a bit of a thing yes.
Have it your way. Show me a single protozoan that has the “lifestyle, behaviour and environmental conditions” of a human zygote. Not sure that makes it any easier.
Then how do you justify belief in universal common descent?
In this video Craig Holdrege talked about the skulls pictured below. If these skulls belonged to closely related individuals it demonstrates the wide variety of forms within one species.
The author of this video postulates that had these skulls been found in separate locations in Africa then they would most likely have been deemed to belong to different species.
Cretology recapitulates Haeckology.
We know because we have both ends of a timeline to study. “Coelacanths are known for their evolutionary conservatism, and the body plan seen in Latimeria can be traced to late Middle Devonian Diplocercides, Holopterygius and presumably Euporosteus”.
If we were studying them from the point of view of an early Devonian observer how would we know that they would turn out to be so evolutionary conserved? Looking at body forms from one instant in time gives no clue as to how that will change over future generations. How would this observer know which fish would have descendants that grew limbs that would enable them to carry themselves out of the water? If they were to even speculate about this happening why would the ancestor of the coelacanth have been one of the contenders?
In the video by Craig Holdrege which I linked to earlier, he begins by asking the question “Where do I come from?” From this point up to the end he discusses the development of animal locomotion and the way that they move. He begins with fish and how they use their whole bodies, then the use of legs by amphibians and reptiles, then mammals arrived and he talks about cats, horses and humans, and compares their leg bones.
Do you think that prior to the arrival of tetrapods an observer would have been able to predict these future trajectories?
I’m sure that he would be the first to admit that his placement of Megachirella within the stem group is provisional on further evidence. Just as placing the coelacanth among extinct animals was provisional and was updated on finding a living specimen.
There is nothing wrong with speculating. Researchers are always making educated guesses, sometimes very educated. 🙂
There is a great deal of death involved in becoming an adult. Narrow definitions kill the language.
In Gorgias, Plato has Socrates say, “But surely life according to your view is an awful thing; and indeed I think that Euripides may have been right in saying,
‘Who knows if life be not death and death life;’
and that we are very likely dead; I have heard a philosopher say that at this moment we are actually dead, and that the body (soma) is our tomb”.
He speaks about death in a living way, how paradoxical is that? 🙂
You see I do learn things here. I’d never heard of that term before, but I like it and I think it points to the way that we should be looking at things. It sees the reality not in a physical specimen at some arbitrary point in time. The reality of any living form lies in the overall dynamic process from its beginning to the present point of observation. And of course the future will become part of its reality too.
I didn’t come here to make communication easy. I came to stimulate my own thinking and if I stimulate other people to research just a little deeper than they normally would and to think more about life then that is a bonus.
🙂
Both exist as single cells enclosed by membranes through which they take in what they need to survive and expel waste. They both rely on an aqueous environment, and on osmotic gradients. They both have the ability to multiply by cell division. They both contain energy generating organelles. No doubt I could come up with more if I thought about it for longer.
In the same way that I know that I came from a zygote but I do not know every detail of how I have arrived at this point from that beginning.
Ah, home of the Minotaur. “Oh what a tangled web we weave”. See Ariadne before you visit. He’s not very nice when he gets his his haeckles up. 😉 🙂
Body plan? Oh dear. This looks like you are focusing on physical details. Me, I prefer to look at lifestyles, behaviours and environmental conditions but maybe that’s just me.
But this can’t be right. First, you are quite mistaken that Latimeria species are morphologically similar to fossil coelacanths. Latimeria, unlike fossil coelacanths, have an oil-filled swim bladder, noticeable differences in the vertebral column, dissimilar skull anatomies and are three times as large as fossil coelacanths were. There is a reason Latimeria were put in their own genus, you know. More importantly, you haven’t shown any direct ancestors of Latimeria. What do the experts know for sure about the actual ancestors of Latimeria? Absolutely nothing! It’s all speculation.
You can’t have your cake and eat it too, Charlie.
Professional paleontologists are neither “speculating” nor “guessing”. You are trying to create symmetry again between your musings and scientific research. They are not on equal footing. If they were, you would be publishing in Nature. Instead, you are on a forgotten corner of the internet chatting with me.
It’s great to hear narrow definitions help language mature.
Bravo, you have just described the majority of all eukaryote cells on the planet. Would it not be more honest to say that human zygotes have radically different lifestyles, behaviour and environmental requirements than protozoans? Unless you can name some protozoans that spent a lot of time moseying down fallopian tubes, that is.
Mmmmmno, that cannot be. You do not actually know that all life derived from a single ancestral cell in the same way that you learned that humans start off as zygotes.
Good luck with looking directly at the lifestyle of fossils which are millions of years old:) But the details of the body plans of fossils can tell us a great deal about the organism’s lifestyle and behaviour.
Anyone interested in the debate over can look at these articles:
Coelacanths are not living fossils. Like the rest of us, they evolve by Lucas Brouwers
Why coelacanths are not ‘living fossils’, A review of molecular and morphological data by Didier Casane and Patrick Laurenti
Coelacanths as “almost living fossils” by Lionel Cavin* and Guillaume Guinot,
There is no doubt that coelacanths have evolved but I think that they show remarkable phenotypic stasis which has been attributed to stabilizing selection. I don’t think you can see the wood for the trees.
One unique feature in living coelacanths you mention is that they have oil filled swim bladders as opposed to air filled bladders. I would argue that this is a matter of degree more than complete novelty. A vital feature of both swim bladders and lungs is the presence of surfactants composed mainly of phospholipids. An oily lining if thickened will eventually fill the whole space within a bladder.
This demonstrates the wisdom of nature in providing what is required for living in a particular environment. For a fish that is constantly moving up and down through a water column an air filled bladder becomes a problem as it needs to rapidly accommodate the changes in pressure. An oil filled bladder alleviates that problem while still helping to control bouyancy.
Anyway, my main argument is to do with the comparison between humans and coalacanths. While both humans and coelacanths are regularly grouped under Sarcopterygii which is derived from the Greek for fleshy fin, only one of the two still has fleshy fins. From the proposed original aquatic lobed finned ancestors come humans with are bipedal terrestrial mammals and extant coelacanths with are, you’ve guessed it, aquatic lobed finned fish.
You have also focused on skeletal differences between extinct and extant coelacanths. Try adding human skeletons into the comparison to see the relative changes over time. Even ancient fossil coelacanths show a wide variety of form while still being recognizable as lobed finned fish.
I am not a professional scientist, I have no interest in becoming one, and I have no urge to publish any scientific papers.
The trouble with maturing is that, if given the chance, it always reaches a natural stage of degeneration.
Yes there is an equivalence between all eukaryote cells taken as individuals and protozoans. Protozoans live in a wide variety of environments. How many do you think will have wandered down the fallopian tubes of some deceased mammal? Life in all forms thrives on death.
Call it a firm belief if you like, but basically I do come to an understanding of these processes in the same way. I have no personal experience of witnessing one of my father’s sperm combining with one of my mother’s eggs. I have been taught by those who have researched these processes that this is how it happens. Likewise researchers have made a convincing case that earthly life began from single cellular beginnings. In both cases I have to rely on, and have faith in what the experts tell me.
I have traced my ancestry back a short distance in time. If it were possible to continue to do so, and as the earth is of finite age, it must have begun at some point in time. I do not believe that any complex physical life form suddenly appeared out of nothing. Life grows like a crystal out of solution.
Just out of interest what are your thoughts, if any, on the physiology of the original earthly life forms?
Looking more closely into the evolution of lungs and swim bladders, with plenty of convergences and lung appearances prior to the eventual colonization of land it would seem that terrestrial life was destined to be. In the same way that lungs are developed in the embryo and formed in preparation for the creatures future air-breathing existence, evolution has prepared lungs in aquatic creatures in preparation for land colonization.
Here is some speculation highlighted by the The Royal Society
So was an oil filled bladder derived from a pulmonary passage? Some fish develop lungs in preparation for air breathing but they degenerate if they are not made use of. If those creatures did not possess the accompanying features which allowed them to make the transition they would have had to remain as water dwellers. No single feature can turn a water dweller into a terrestrial animal. It requires the development of a suite of features to migrate onto the land. Looking at the metamorphosis of amphibians gives us a good idea of what those features are and what changes are required.
CharlieM,
Minotaur with his ha(e)ckles suitably raised. 🙂
OK, good to know.
I know you are not a professional scientist so I wonder how and where you learned this fact?
I learned this from reading and listening to professional scientists. Here they write:
Here we read:
I have known about lungfish for years, but so far I haven’t studied lungs in fish in any detail.
I know you’re not keen on videos but here Neil Shubin of Tiktaalic fame states that in fish air breathing evolved at the very least 24 times and the most common way they do this is by the use of lungs. (yet more convergent evolution 🙂 )
I have read that during development some fish form two lungs, but only one develops into a functional lung while the other one degenerates. I don’t have the time at the moment but I’ll try to find references for this if you like.
CharlieM,
What I was querying was the implied Lamarkianism. Individual organisms don’t evolve; populations do.
Why are we allowed to use morphology in linking Latimeria to extinct coelacanths and concluding it shows stasis, but not to link frogs to their ancestors and decide there never was an evolutionary tadpole stage?
Again, what makes you say that Latimeria are coelacanths? You have no access to its direct ancestors so this could simply be an example of convergent evolution.
Then on what basis should humans be grouped under Sarcopterygii? We do not have direct ancestors linking humans to fossil Sarcopterygians. It looks like Sarcopterygians just met their demise.
I am being a bit facetious here, but the point is that quite a lot of your arguments rely on reasoning that you have been actively undermining in previous comments. Neither can you appeal to the authority of paleontologists or taxonomists, whose work you have been dismissing as “speculation” and “guessing”.
Welcome to TSZ!
Precisely zero. I do not see any “similarity of general lifestyles”.
Individual development may not be passed on down the generations but during this development organs do change over time which reflects the change over time of evolution on a lager scale.
Never collected frog eggs to see them develop into tadpoles? Now there is a parallel with human development that is actually valid.
Like you, I need to rely on expert opinion in fields I am not familiar with. What is remarkable is that whenever you don’t like expert opinion, you suddenly start viewing it as baseless speculation. This attitude evaporates as soon as you perceive some piece of information to be congenial to your own point of view, even though it relies on exactly the same methodology.
Currently I am reading the (ridiculously slim) Origin if Life: What Everybody Needs to Know by David Deamer. The picture of very early life is still very vague, but it looks like the building materials of life (amino acids, nucleobases, carbohydrates) were present on early earth. As I understand it, exactly how these came together to form a living being remains an open question.
The first cellular beings must have been very different from what we see nowadays. I do not believe them to have been anything like modern bacteria, nor like the zygote stage of multicellular organisms. All living things today have evolutionary roots extending billions of years into the past. I am convinced a lot of changes must have happened during that period.
But of course it is, it has to be.
There is no change in the organism’s genome and it is the genome that carries the necessary information for the zygote to develop through all intermediate stages to adult The key is heritable change. Mutations in the germ-line result in different phenotypes (smaller, larger, darker, lighter etc) and their differential ability to survive and reproduce given a specific niche is the engine of evolutionary change.
Not familiar with the lager scale. The old saying “ontology recapitulates phylogeny” comes from the defunct biogenetic law championed by Haekel, who was so enthusiastic about his ideas that he saw and drew things that weren’t there much to his discredit.
https://en.wikipedia.org/wiki/Recapitulation_theory
When I say it shows stasis I am just repeating what the experts have said. In the case of coelacanths conclusions are being made on what actually exists. In the case of amphibians such as frogs their evolutionary history is not so easily discernible. But it is a common belief that amphibians evolved from fully aquatic ancestors. Being fully aquatic is one of the feature they have in common with present day tadpoles.
I don’t mind speculating on it being a case of convergent evolution if you don’t 🙂 But Latimeria does come under the common name “West Indian Ocean coelacanth” or “West Indian Ocean coelacanth or Indonesian coelacanth depending on species.
If we accept that coelacanths, frogs and humans all had ancestors that existed half a billion years ago we can say that it is generally thought that all of these ancestors were aquatic. So in comparing the free living stages of all three extant creatures with their ancestors at that time we would get:
Human – ancestor was aquatic, extant is terrestrial
Frog – ancestor was aquatic, extant is aquatic/terrestrial
Coelacanth – ancestor was aquatic, extant is aquatic.
This is one regard in which stasis applies. Or if we assume convergence, reversion to an earlier condition.
An interesting exercise is to compare the basic lifecycles of coelacanths and frogs
The coelacanth life cycle is described here
In the general lifecycle of frogs that produce tadpoles, the tadpoles develop in eggs which have been laid by the adult frog. They then develop in a free living fish-like phase later to undergo metamorphosis into adult frogs.
In most cases the tadpole to frog stage is undergone in open water whereas the equivalent stage in the coelacanth happens with the protective body of the mother.
The variations observed within nature have a lot do do with expansions and contractions of processes within time and space.
Sarcopterygians do meet their demise in humans. Every time a baby is born and that person transits from an aqueous existence to a terrestrial existence they they behind their fish like life, it is dead to them.
But I can look at the evidence that these experts have brought to light and interpret it in a logical way. Even among the experts there is both agreement and disagreement, so in agreeing with one expert I could very well be disagreeing with another.