Show from Darwin 6. Turtle - fiction or reality?

6. Turtle - fiction or reality?

"The most remarkable feature of turtles is their shell. How did it evolve, and what were the intermediate species like? Where are the missing links? What is the use (a fanatical creationist might ask) of half a shell? Well, that's great, a new fossil has just been described that eloquently answers these questions."
This is a promising beginning – a quote from the esteemed Dawkins. Answering the question of a "fanatical creationist," he reports on the discovery of fossils of an aquatic turtle (Odontochelys semitestacea) found in late Triassic sediments in China. This fossil is estimated to be 220 million years old.

Unlike the modern turtle, it had teeth, a much longer tail, and-according to Dockins-half of the shell. As he reports: "All three of these features characterize her as suitable for the role of the "missing link"."
In fact, what is not a "transitional form"? This prehistoric turtle has a one-sided shell, which covers only the belly, which makes it related to the modern sea turtle. The only difference is in the absence of a dorsal shell.
Having presented the transitional form, Dockins does not ignore the evolutionary significance of this find: ""What is the use of half a shell?" In particular, why should Odontochelys be covered with armor from below and not from above? Perhaps because the danger threatened from below, which means that these creatures spent a lot of time swimming near the surface — and of course, they had to come to the surface to breathe.

Sharks today often attack from below, sharks must have been a threatening, important part of the Odontochelys world, and there is no reason to believe that their hunting habits were different in those days."
The argument in favor of maintaining such an intermediate form by natural selection sounds more than convincing.
That's it! The topic is closed. There is an intermediate link, there is a convincing passage through the control of natural selection.
Maybe something is wrong? But what?
We were presented with two beings, one of which is a transitional form of the other. This intermediate link is the missing link between the modern turtle and its shell-less progenitors.

Yes, we remember that the intermediate link is an unscientific archaism, since it is almost impossible to detect differences between the samples presented. They look like twins to each other. Why, their own mother will not distinguish them from each other, not like natural selection. Isn't that right?
Is this the evolutionary step Darwin had in mind? Dockins himself was thinking about such gradualness when he talked so intriguingly about rabbits and about such a gradual evolution that should not "explain anything."

I doubt. Each of the presented creatures is separated from each other by a considerable number of intermediate imperceptible mutations. To grow a double-sided shell unnoticed by their relatives, it takes oh, what a considerable time. And finally, the difference between them is visible to the naked eye!
A lot of questions immediately arise. Could the water turtle Odontochelys have been born to shell-less parents? Could these parents have failed to notice their cub's shell? And the most curious thing: would this creature find a mate among non-mutated relatives, and if so, what kind of offspring could they have?
Even more interesting is the very possibility of getting a shell (whether abdominal or back) one before the turtle generation?

Someone will ask: why in one generation?
Judge for yourself. We are presented with one "intermediate link". And even though "we don't need fossils — the matter of evolution is iron and without them," let's still try to present this "iron" at least as a logical reasoning.
Since, just as in the example with the angler fish, it is not possible to find Dockins' arguments in support of quotations from Darwin and his own conclusions, we will have to take this work on ourselves again. Let's try to walk the evolutionary path between these creatures instead of the professor. Let's say from Odontochelys to the modern turtle.

But before embarking on the evolutionary path, let's assess the depth of the problem: let's ask in the encyclopedia what the shell is. It is known that the shell of a modern turtle is very strong, in some species it can withstand a weight 200 times greater than the mass of the turtle itself.

The dorsal shield of the carapace is called a Carapace, has a convex shape and consists of a bone base and a horny coating. The carapace of typical turtles consists of about 50 bones — plates of mixed origin. Skin derivatives (osteoderms) are involved in the formation of the outer (epithecal) layer. The middle (tecal) layer has a mesodermal origin. The elements of the endoskeleton are attached to the tecal layer from below: spinous processes and upper arches of the trunk vertebrae, and ribs. Most often, the shell has two layers: internal (bone) and external (keratin). The bony layer of the shell is made up of plates, and the horny layer is made up of shields. The high strength of the shell is partly due to the fact that the boundaries between the inner plates and the outer shields do not coincide.

There is a lot more written in the encyclopedia, but it is already clear that the carapace is a surprisingly strong structure. In order for natural selection to start supporting Odontochelys mutations in favor of such a powerful defense from above, something must have happened in the distant past.
What could it be? Changing the habitat, changing the tactics of predators. Doesn't matter. The important thing is that the protection now needed was comprehensive. It was necessary to urgently build up the double-sided shell.
Why is it urgent? Yes, because it is very difficult to imagine predators that from generation to generation so imperceptibly change their tactics that you can safely grow a shell. Or such a gradual change of habitat so that, say, land predators do not notice a new defenseless addition to the menu for hundreds of generations. In any case, the poor Odontochelys would hardly have had time to lay eggs in order to appear before us in all their armor.

Of course, any reasoning is probabilistic. It is possible that something unusual happened during the growing of the double-sided shell. For example, all predators were struck by some kind of general epidemic - a kind of prehistoric coronavirus. Or they suddenly hit veganism. However, then the question arises, why grow a shell at all? For growth? It is unlikely that natural selection would like it. After all, in the absence of predators, there is no point in such a cumbersome defense.
Okay, let's try to go from the other end: let's imagine a very gradual evolutionary path from a shell-less ancestor of a turtle to its one-shell relative. We will make this path again, not anyhow, but exclusively under the strict control of natural selection.

To begin with, let's try to imagine a shell-less ancestor of a turtle. This creature had to have a certain set of properties that allowed it to survive. It can be the ability to run fast or swim, deftly dodge predators, have strong teeth, etc. Choose any or all of them according to your taste.
This creature successfully survived without a shell, otherwise it would not have been able to leave offspring, which would later evolve into a turtle. Now imagine that one of these individuals has mutated. It could have been a single gene mutation or, less likely, some larger mutation. It is important that, regardless of its complexity, the principle of randomness was not violated and we would not be able to notice significant differences between the mutated individual and its relatives.

So, a certain ancestor of the turtle has the beginnings of a shell. In principle, we have only two variants of the evolutionary movement. Layered thickening of the shell or the formation of single shields, subsequently combined into a single shell. It does not matter which path was chosen by evolution, it is important that these changes are gradual and imperceptible against the background of non-armored relatives.
Well, what will natural selection say to this? And selection should be checked at each stage (read, generation) with such an important characteristic as survival. If the mutation gives the mutated individual even the slightest advantage, then the green light turns on.
What are these advantages? First of all, the ability to get the necessary food and protection from predators. The shell is a good solution to the second problem.

But what is the rudiment of a shell? This is an increase in body weight, which inevitably leads to a decrease in speed and agility. What does a hypothetical mutant get in return? A single shield or seal of low strength, which almost does not improve the protective functions of the body.
The appearance of a rudimentary shell for predatory teeth is not an obstacle. Even on some N-th mutation, the shell formation, even a quarter of the required strength, will not fulfill its purpose.
The first mutated individual, as well as thousands of her descendants who intend to gradually build up the shell, will have to wear a bulky education, spend the most valuable energy resources on its growth. At the same time, lose in agility and speed of escape from a predator. As much as we would not like, but from generation to generation, individuals growing a shell will lose to their relatives in the competition.

The shell in its fully formed form performs such a function and more than compensates for the sluggishness of the turtle. Whether on land or in water, a half-shell will not help its owner to escape from the teeth of a predator. This is just a useless load on the body, which does not perform its protective functions. Most likely, natural selection will consistently reject each generation of mutants who are unable to protect themselves with the prototype of the shell and who have lost the speed advantages of their ancestors.
A good solution to this problem would be parallel evolution, in which the pressure force of the jaws of predators increased in proportion to the protective strength of the shell. Then the reinforcement of the shell would fit perfectly into the requirements of the theory.

That's just bad luck. Scientists have made such good progress in studying the remains of dinosaurs, have released so many popular programs describing the colossal power of prehistoric predators that they have not given our poor turtles the slightest chance. Moreover, based on these studies, it should be concluded that the ancestors of modern turtles needed a shell even more powerful than the living ones.

The fossil of the water turtle Odontochelys is estimated to be 220 million years old. By that time, dinosaurs had been establishing their order on the planet for at least three hundred million years and died out another hundred and fifty million years later. And after them came no less saber-toothed successors. So all along the evolutionary path of intermediate links, turtles were waiting for extremely powerful jaws of predators.

Nevertheless, let's meet our turtles halfway and assume that a grandiose evolutionary step has taken place, as a result of which a mutant was born with a fully formed inner layer of carapace from a complete set of plates. Natural selection, of course, could not sleep through all the intermediate links leading to it, because these mutations lost in the struggle for survival.
To help our turtles comes the synthetic theory of evolution (STE), which supplemented Darwin's theory with genetic knowledge. She explained the accidental appearance of new signs by mutations - changes that occur in the DNA of organisms. Geneticists have found out that not one gene, but a group of them is responsible for the development of a particular trait. A single mutation usually does not lead to the appearance of a new trait. The newly acquired gene is in a recessive state, not manifesting itself in any way, until other mutations help it.

According to STE, natural selection does not act on individual genes, but on groups of genes that accumulate over an indefinite number of generations. Therefore, natural selection can sleep peacefully while grandiose changes are maturing inside the ancestors of turtles.
Then, let's assume, thanks to the knowledge of the STE, that a fully formed inner layer of the carapace was born. Such a shell initially became almost half of the strength possessed by the shell of a modern turtle. In fact, it is far from half the strength, since the amazing strength of the shell is largely caused by the presence of a layer between the inner plates and the outer shields.

So, this is not yet the creature that was found in the form of a fossil and received the name Odontochelys semitestacea from scientists. It's a creature standing somewhere halfway to Odontochelys. By the way, this is exactly what a shell looks like when you read the question Dawkins asked himself (What is the use (a fanatical creationist might ask) of half a shell?).

The resulting creature should already be truly clumsy, deprived of almost all the advantages that its ancestor possessed, and at the same time a half shell will have no more than half of the required strength. You can't hide behind such a structure if a predator overtakes you. A shark, as you can guess, will not be stopped by a shell of half strength or, say, half the area of the body.
Whatever one may say, but in order for natural selection to approve the appearance of a born mutant, it must have a fully formed shell. Well, such a hypothetical possibility is provided by the synthetic theory of evolution. There are still some difficulties with violating an important postulate of the theory of gradualness and sexual selection, but I think that smart geneticists will easily find an answer to this question.

However, if we agree that karapax was formed as a result of a series of mutations of genes remaining in a recessive state, then along with purely scientific problems, there is also a political one.
Engineers and scientists around the world have been improving armored vehicles for more than a hundred years. Research institutes, scientific design bureaus, thousands of scientists have not yet been able to equip modern military equipment with such heavy-duty armor, and nature has been able to rely solely on chance and without any assistance from our wonderful natural selection.
It turns out that thousands of scientists receive billions for their research and cannot do what can be obtained by random poking. I'm afraid that this is not only a dubious assumption, but also an insult to the entire domestic military-industrial complex.

It is especially sad in this situation that not only in Russia this assumption can be equated by certain authorities to high treason. As far as I know, the multibillion-dollar US military budget also failed to cope with such a simple task, and the establishment on Capitol Hill is very sensitive to everything that, in their opinion, threatens US national security.

I don't know about you, but I don't want to cast a shadow on the military-industrial complex, and therefore I am doubly eager to follow the theory. If there is a certain statement, then, as it will not seem strange to someone, and it is this statement that needs to be proved. Then if something is wrong, it will be possible to blame everything on... natural selection.

Well, every theory should have exceptions. Perhaps the turtle is just the case. Anyway, my liquid brain can't come up with a reasonable excuse for her appearance. Of course, this is just my problem, but given the complications that have arisen with the military, it is still worth excluding the turtle from the real world of nature and placing it in a number of mythological creatures (somewhere between a dragon and a unicorn), the existence of which is spread by malicious opponents of the great doctrine.

Well, in fact, the turtle does not give milk, although it carries eggs, but everything goes past the refrigerator, so I personally readily admit that there are no turtles on our planet and never have been. And those who will claim the opposite will be branded in an anti-scientific approach to nature.
But seriously, no matter how sad it was, I couldn't cope with this example and I'll have to look for a new one. In general, the task that seemed so simple at first turns out to be more and more intriguing.

* - I apologizes for my English. I would be grateful for the corrections.

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