Two separate groups of researchers studied the adaptation of animals to the toxin produced by the organisms they eat. The toxins in both cases are very similar: both attack a specific protein
When Darwin wrote "The Origin of Species", the form in which evolutionary changes occur - the molecular mechanisms that are responsible for the heritable variation that played such an important role in his theory - was a signature book for him. The science of genetics took its first steps just then, in the pea garden of the monk Gregory Mendel, but it is doubtful whether Darwin was aware of it at all, and in any case he did not understand the importance of these experiments.
In the hundred and fifty years that have passed since then, genetics has become one of the most successful fields in biology, and has recorded impressive achievements: the hereditary mechanism was identified as the transmission of discrete entities called genes, which later turned out to be a specific sequence of DNA bases. The DNA structure is deciphered and the code that enables the conversion of DNA into proteins is also cracked. Genetics has influenced many different fields, from medicine to evolutionary research.
Today, researchers are able to examine changes in the DNA molecule, which lead to evolutionary changes. This is what two groups of researchers did - one with researchers from the Universities of Utah and Indiana in the USA, and the other with researchers from the Institute of Marine Biology in Halifax, Canada, and other universities from the USA. Both groups studied the adaptation of animals to the toxin produced by the organisms they eat. The toxins in both cases are very similar: both attack a certain protein, which creates a channel that transports sodium ions across the cell membrane. This channel is found mainly in nerve cells and muscles, and is common throughout the animal kingdom. When it does not function, the nerve cells are unable to transmit signals and the muscles are unable to contract in response - therefore, the toxins that damage this channel may cause paralysis and even death.
The animals in question, however, are very different. The Canadian-American group studied a type of clam, which feeds on microscopic aquatic creatures, including different types of algae. One of these types, the same algae that cause the "red tide", contains the toxin Saxitoxin. Certain oysters are able to store the toxin in their contents after eating the algae, and animals that eat the oysters - including humans - may be paralyzed. But the oysters themselves are also sensitive to the toxin. The researchers tested their sensitivity with a simple test - how well the oysters manage to dig in the soil when they are placed in a new location. The saxitoxin damages the oysters' muscles and thus makes digging difficult. When they compared oysters from two different locations - one place where the algae bloom called "red tide" occurred every summer, and another from a place where no red tide events were recorded - considerable differences were observed between them. The toxic algae damaged the function of about 86% of the oysters that had not been exposed to this algae before, but only the function of about 10% of the oysters "accustomed" to the algae. Longer exposure killed more than a quarter of the sensitive type of oysters, but less than 2% of the other type. If so, oysters that are regularly exposed to algae have developed a defense mechanism against the toxin. What is this mechanism? To test this, the researchers isolated the nerve cells of the oysters and directly tested the sensitivity of the cells to the toxin. Again, large differences in sensitivity were found between the populations: that is, the difference between them is found in the cells themselves.
The next step was to isolate the specific gene responsible for the production of the sodium ion channel. It turned out that in the gene found in the oysters resistant to the toxin there is a mutation in one DNA base, which changes a single amino acid in the protein sequence of the channel. The mutation is in a place that has already been found in previous studies as the binding site for toxins of this type. To test whether this mutation is really what confers the resistance, the researchers took the gene that codes for the same channel, but in mice, and induced the same mutation in it. The gene was expressed in a bacterial system, creating a protein that is almost entirely murine - but it carries the mutation of the resistant oysters. When they exposed the isolated protein to saxitoxin, the researchers found a certain concentration of the toxin that almost completely prevents the normal channels from working - but in order to lower the activity of the channels in which the mutation was only about 25%, a thousand times higher concentration of the toxin is required.
This experiment proved that this single mutation allowed the oysters to resist the algae's toxin, and this new trait spread to the population that needed it—the one that was regularly exposed to red tide.
The second group, the American, studied snakes. Garter snakes feed, among other things, on newts - and some of these newts produce a toxin from the same family as the saxitoxin - called Tetrodotoxin.
This toxin also has a culinary aspect - it is the same toxin produced by the fugo fish (Abu Nafha), which is served in Japanese restaurants to especially brave diners, after the cooks try to remove the organ that produces the toxin in its entirety.
In this case, similar to the case of the clams, there are large differences in sensitivity to the toxin between different populations of garter snakes. The researchers tested 4 populations of snakes from different places in the United States where poisonous newts are found, where 3 of the snake populations had some resistance to the toxin - although some were more resistant than others. As a control, the researchers also tested a population from a further place, where there are no poisonous newts at all - and correspondingly, these snakes have no resistance to the toxin. When they analyzed the evolutionary tree of these species, the researchers found that two of the resistant populations were closer to the non-resistant population than to the third resistant population - that is, the resistance trait evolved at least twice in these snakes, in response to the toxicity of the newts they ate.
The next step was, again, to test the sodium ion channel where the toxin affects. The researchers identified a very small area in the protein - no more than 15 amino acids - where there were mutations in the resistant populations, but each population had slightly different mutations. To test whether this is indeed the thing that confers the resistance, they took the same action as the group that studied the oysters: they took a protein that is known to be sensitive to the toxin - this time not from a mouse but from a human - and replaced the specific section of this gene with the client section from the shield of a resistant snake. The researchers checked what concentration of the toxin is needed in order to lower the channel activity by 50%. When the researchers performed the experiment on a protein carrying the mutations found in the most resistant population, it became clear that the required concentration was three orders of magnitude higher compared to the protein taken from a person, or a non-resistant snake. Mutations found in less resistant populations made the human protein resistant to a certain extent - a sort of intermediate state between the mutations of the most resistant population and the original human gene. This is how the researchers showed that these mutations, which apparently developed independently in different populations, are what give snakes the ability to eat the poisonous newts.
Both studies show how genetic changes in a single gene can impart a new trait, which is very important for survival - resistance to poison produced by potential prey. They also show how this trait spreads only in populations exposed to the poison, due to natural selection pressures. In garter snakes, it seems that adaptation to the toxin is in full swing - when different mutations develop in each population, conferring different levels of resistance. This is how molecular changes lead to evolutionary changes - and ultimately to the development of new species.
Snake man - about poisoners and poisonings in history
32 תגובות
Raanan (March 21, 2009 at 12:57 pm)
You wrote: "The philosophical question is whether neutral DNA exists in definition number 2 of the long term"
This is a probabilistic question. As a rule, there is a certain probability of a mutation that will cause a certain gene (or any functional DNA segment) to lose its function. In principle, if that DNA section does not function in any essential way for the existence/survival/reproduction of the organism that carries it, then it can be called garbage for the purpose of the discussion. The same segment can accumulate additional mutations and still remain over time a roleless and meaningless segment in terms of the functioning of the organism. There is no principle preventing that segment from remaining like that until the end of life, alternatively, the segment can return to be useful due to a mutation or disappear (for example, due to a missing mutation which results in the segment leaving the genome completely) and these possibilities also have a probability of their occurrence (sometimes it is even possible to estimate what the probability is will happen). I didn't quite understand why you presented it as a philosophical question...
In relation to your earlier question, in principle a neutral trait may also be fixed in the population through a mechanism called genetic drift, where the smaller the population, the more significant this mechanism is and can lead to the fixation of neutral traits faster (in the theoretical model it is possible to create a situation where by definition the trait does not confer any advantage and still fixation is a result always possible). Regarding existing features or DNA segments whose function is unknown, it is in principle possible to perform experiments that examine possible contributions. Of course, any negation of a proposed possibility still does not prove that there is no other function, but it would be reasonable to call this segment a junk if it is found that it does not express itself, does not affect the expression of other genes, does not affect replication processes (such a thing can happen, for example, just by its presence the physical in the space that moves other functional sections apart or closer) and in general no difference can be identified between a state in which it is present or not present. Bringing up adaptive explanations (as you did above) are somewhat pointless without examination and research because the complex reality we live in shows that, like Hamitzer riddles, there are many answers that seem to fit very well. I know two people who have developed a hobby of convincing someone of an adaptive explanation and then showing how the opposite adaptive explanation is equally logical and intuitive. An examination of adaptive explanations should be done very carefully and not just in a thought experiment. In everything related to nature, our intuition often leads us astray. In this context, an abysmal difference between science and religion is that in the former there is a built-in mechanism that brings us closer to a reliable description of reality, while in religion there is a mechanism that builds a wall of excuses that will "explain" why the beliefs at its core are so inconsistent with what turns out to be the correct description of reality.
fresh:
It's just tiring because, as mentioned, you're left with a claim that doesn't mean anything but you keep waving it around
I have explained what I believe in the best way I can and I have not yet read an explanation that convinces me otherwise, but then again I may be wrong.
This time span is a term that compares 2 time points. Since inevitably over time all the genes will eventually disappear. And there is a chronology of disappearances such that first the harmful genes will disappear, then the neutral genes, and finally the good genes, so there will necessarily be a point in time when the genes that today we call neutral will disappear, and we will compare this point in time with an earlier point in time when these genes were common in the population, the interval Between these 2 points of time is the definition of a long time span, since for each gene there is a relevant time point of existence in Och and disappearing from it, then the value of the number of years for the long time span will change accordingly for each gene.
fresh:
It seems to me that you have accepted all the arguments and you continue to present the "philosophical question" only because you do not want to give up everything.
This "philosophical" question is sufficiently vague that it cannot be answered (simply because it is impossible to know what it is).
What is "long range"? After all, as you said - at some point there will be no more life, so nothing related to life has an infinite range.
Junk DNA does not serve the individual.
It remained in the genome only because it was not evolutionarily "payable" to sift it out. It is not there for any specific need and purpose, even though under certain conditions it may be useful. This is a feature of garbage in general, so there is no point in saying that it is not garbage just because we might ever use it. If everything we might ever use is not garbage then there is no garbage in the world at all. Why did they bother and invent this word, if so, and doesn't its very existence (as linguistic garbage) contradict this definition of the term garbage?
Roi Hatha is right that there is no necessity for the genes to play their part (with an emphasis on the word necessity, and with an emphasis on the fact that the time span is not billions of years) In addition, the entire universe can be seen as a closed system that is gradually eroding towards chaos, this is the general rule, this rule has special cases such as the mind An animal that apparently exists violates it by its very existence. Because life is a material with "order", but this living order is inevitably eroded as time passes. So that "order" can "win" over chaos but only in the short term, in the end (TA in terms of billions of years, not millions) everything will play out, even useful DNA, and of course the neutral DNA will play out immediately after the DNA the pest
And this is of course subject to the fact that DNA that is harmful at one time-space point can be considered very useful at another time-space point.
And as I said in the short term there certainly exists useless and harmless genetic material, but the philosophical question is whether neutral DNA exists in definition number 2 of the long term.
fresh:
I want to put my words in the right context so that those who read them will not make a mistake in their interpretation.
In a certain sense - different, in my opinion, than what you meant, you can accept your words as true, but then you shouldn't have had any argument with anyone in the first place.
Since evolution is built on mutations, the existence of a rich genome, part of which is not functional, may be an advantage in that it provides a wide base for new mutations that do not come at the expense of necessary genes.
It is possible, therefore, that evolution has "favored" organisms that have a tendency to accumulate a certain amount of junk in their genome.
Under such an interpretation, it can indeed be claimed that this garbage is insurance for the future, but there is nothing new in this type of claim at any given moment - the garbage that you find in the genome is simply garbage that may or may not be used in the future.
It is somewhat reminiscent of people's tendency to collect.
There are those for whom it is really a disease and they are unable to throw anything away. Their houses are filled with garbage and their lives are destroyed.
There are those who throw away anything they don't find an immediate use for - these often find themselves regretting having thrown away something that they now need.
Most people do not belong to either of these two extremes and keep (to an extent) even things that they do not know what they will do in the future.
fresh,
Let's start by saying that the law of entropy is not acceptable for the earth system, because it is not an isolated system, but receives energy continuously from the sun. The same for living organisms. So there is no necessity for the genes to wear out over time on their own.
Furthermore, you claim that junk DNA has a use, because it enables future genetic variability. I believe you're right, but that doesn't mean it has an immediate use that benefits the organism it's in, and that's what we're debating at Bethel.
If anything, your argument - that junk DNA has a future use - only proves that every organism must have a lot of useless genetic material, because this genetic material is the junk DNA that will mutate in the offspring of that organism and help in sensing evolution. But this only means that every organism has a lot of genetic material that is not useful, and sometimes even harmful.
fresh:
This is a very strange answer.
Do you think the junk is kept in the genome for a specific purpose?
Is there anyone out there who knows that it will come in handy in the future?
This is utter nonsense.
It also completely sterilizes the discussion because every time you are pointed to garbage in the genome you will say that it is there to serve a future purpose. Such a claim cannot be refuted and is therefore not scientific.
I have already mentioned that JUNK DNA is not really pointless, because it can be seen as a pool of genes that provide as a spring an insurance policy for survival that shortens the waiting time for the adaptation that will help in survival, and I will explain:
Creating a good gene/mutation/adaptation from scratch can take nature a long time (this time will be very difficult to impossible for those who do not have this adaptation.)
This JUNK DNA is a garden spring in near perfect condition that only needs a slight modification to get back to working. And so nature saves the time from the lengthy process of creating an active garden from scratch.
Of course there are genes that remain inactive for millions of years and recently we read an article here in science about genes that were inactive for millions of years in monkeys and returned to activity in humans.
If someone wants to claim that they had a function in the intermediate period they should also explain how the person lived without this function.
In my opinion, the reason that genes that are neither useful nor harmful must disappear in the long term is a law of nature called entropy, which erodes not only genetic material but everything including everything, therefore for something like genetic material to survive in the TA it is not enough that it be neutral, it has to be actively beneficial, Otherwise nature will wear it out over time, and in the long run even all the genetic material that is useful will wear out, so all the more neutral genes (which will wear out much earlier)
Is there a world-renowned biology professor who claims what I believe (or the opposite) who has done serious research on this subject? What is the "accepted opinion" today in biology on this subject?
fresh,
Nature strives for efficiency, as you say, but this is a 'local' efficiency. It relies on the previous configuration of the organism. If the organism carries "genetic remnants" from previous generations, there is no certainty that they will be eroded during evolution.
There is a high probability that some of the harmful residues will disappear, but there is no need for all of them to disappear.
When I read your analysis, I get the feeling that you have already reached a conclusion and you are trying to justify it with many hypotheses. Try to simply accept the premise I outlined for you - that in the short term, non-beneficial genes can remain in the organism and its lineage - and explain to me why those non-beneficial (but also harmless) genes will inevitably disappear over millions of years.
Every long term is also a short time term of a recent time, of the last few years (it can even be a few thousand years ago) but every long term, in addition to being a short time term of a near time period, is also a long time term of an old period ( from millions of years ago) and refers only to her.
In other words, the phrase long time span can be understood in three ways:
1 which refers to a recent period of time (thousands of years)
2 which refers to an ancient period of time (millennia of years)
3 which covers both a recent time period and an ancient time period.
And in my opinion, the lack of agreement is not real but stems from the ambiguous definitions of words and terms (such as a long period of time).
When I talk about the long term, I mean it in the sense of: the genes that exist today, in relation to the genes that existed in the same organism millions of years ago. If a comparison is made between genes that exist today and genes that existed in the same production millions of years ago, the likelihood that a gene without a function (without an objective and real function, as opposed to a simulated and subjective lack of function, which may arise from our ignorance) will survive the millions of years is zero because from a physical point of view (and therefore necessarily also chemically and biologically) it is inefficient and nature strives for efficiency. Of course, if we are talking about defining a long time span (no. 1 or 3) then the probability of finding genes without a function will necessarily be 100%.
That is, at any given moment there will always be genes without a function, created in a short period of time by chance, or even a gene that already existed in the past and became extinct (and returned to existence randomly for independent development again.)
But there will be no genes without a function, which have a lineage that extends over many years.
An explanation for the disappearance of hair..
In cold and beautiful Europe they used to organize parties full of fire, heat and alcohol. Part of the effects of drinking was that the celebrants would get too close to the fires, or it was part of an accepted game. which caused the thinning of the hairs.
fresh:
I already said in another discussion and I think it is relevant to this discussion.
Bald or not bald or any other example - none of this really matters.
What is clear is that natural selection is only possible if there is variation.
Among the variations, the most suitable one is selected over time, but this means that at any time there are also less suitable variations.
In other words - the animals are never optimally adjusted and there are always individuals in the population with "redundant" genes and individuals with "missing" genes.
Which beneficial changes will become clear only over time, and therefore the term "redundant" or "deficient" only becomes clear after the selection has taken effect, but all this does not change the principle according to which - if there is someone who is more adapted than others, then all the others are less adapted than him and certainly it cannot be argued They must have their DNA perfect and nothing superfluous in it.
fresh,
In the end, there are many hypotheses, but I think you can agree with me that in the short term, genes that are not beneficial, can actually survive. But evolution is ultimately one short time after another. Sometimes it removes from the organism the features that are not necessary for it. Sometimes she adds others to it. I assume that the principle of natural selection makes sure that the process does not get out of control, and that there remain organisms that can still minimally compete with their peers / rivals.
The principle of weighting with the huge peacock tail created by mate selection really reduces the peacock's chance of surviving in the wild but makes up for it in terms of the chances of culture. And regarding gene spread as a result of randomness, I think it could make sense in the short term from an evolutionary point of view. But in order for a random gene to survive in the long term, in my opinion there must be something that actively contributes to the survival of the organism (at least contributes to survival in a certain environment) There is a new book on this subject that I just started reading today and it seems interesting to me, and it's called "Precisely the weak survive" by Dr. Sharon Moalem
This also has a hypothesis: many Europeans have curly hair with a swollen mane, and this can insulate against the cold really well, for Africans the Afro "stands" against the forces of gravity so that on the one hand it creates a shadow and on the other hand it does not heat up the back of the neck/shoulders too much.
But since there is no way to check if all these hypotheses are correct it is something more philosophical than scientific.
Reverse hypothesis:
In Europe it is very cold in the winter, so there is also a need for curly and dense hair to protect against the cold.
So again we didn't make any progress, and we didn't explain why the hair disappeared in Europe.
Another hypothesis: in Africa there is high UV radiation, it is necessary to protect against it, therefore the curly and dense hair of the Africans provides good shading.
fresh,
Matrimonial selection is not equivalent to natural selection. Mate selection can, in many cases, not be affected by the advantages or disadvantages that the mutation gives to its bearer. Hence, it is a mating selection, it is clear that the mutations can remain even though they are not beneficial.
Beyond that, the example I gave does not concern mate choice, but randomness. The head of the tribe was, quite by chance, also bald. This could have been enough to start the chain reaction that resulted in the baldness of Europe.
You gave examples that explain the development of baldness from the point of view of the sexual barrier and I gave from the point of view of natural selection, both can be correct in my opinion.
Regarding hoods, I assume that not all human periods wore hoods, and even when they did, not every member of the population wore it, even if we go to Europe today, not everyone will be wearing hats. And there are places where it's less cold and you don't need a hood, but there's no sun that gives vitamin D, like for example a tangled forest.
Indeed, the fact that UV radiation is low does not mean that baldness is necessary, but perhaps nature tends not to invest resources (growing hair can be seen as a type of investment of resources and energy that can be saved) where they can be saved, that is, it tends to efficiency and minimum energy) but it could certainly be just a hypothesis wrong.
fresh,
Even if the UV radiation is indeed lower in Europe, this does not mean that baldness is necessary, so this hypothesis is not relevant. As for vitamin D, that sounds dubious to me, especially given the hoods that Europeans tended to wear in the European cold.
By the way, you can continue to wonder: why do humans have a tailbone? Why do Indians have eagle noses? Why is the skin of the Asians yellowish / why are they short / why are their eyes slanted / why are they less hairy than the other groups (all on average and in general, of course)?
By the way, of course in the long run there is no redundant hereditary material. Any hereditary material, including the junkiest DNA, can undergo several mutations and become a gene that improves the mutant's chances of survival in its environment. But we are talking here about immediate benefit, and the reason that significant genetic material remains and even spread in the population.
I'll give you another example...
At the time of the migration to Europe, 30,000 years ago, only a small group of people migrated - say fifty people. The head of the tribe had a random mutation that made him bald. In the manner of tribal leaders, he had ten wives. Each gave birth to three children. In the next generation there were thirty children who tended to go bald, and only forty-five other children (assuming there were 25 women in the group in total) without the tendency to go bald.
Now suppose that one of the children who tend to go bald becomes the head of the tribe himself and takes ten more wives. Very quickly we will accept that the relative amount of bald people in the same tribe increases from generation to generation.
If, after several such generations, the tribe begins to spread throughout Europe, then we will accept that most of the descendants of that tribe will carry with them the genes that lead to baldness at a young age - and this without them increasing or decreasing their chances of survival to a noticeable degree.
This is how we accept that a mutation - even to the extent that it does not help an individual or society - can indeed spread within several generations to the entire population. Unless extremely strong negative selection is applied to it (for example, an epidemic that affects all balds), it simply won't have a strong enough reason to disappear.
Hypothesis: In Europe, the UV radiation is lower than in the rest of the world, therefore there is no need for hair to protect against this radiation which is known to be carcinogenic, in northern places there is a real lack of radiation which can lead to a lack of vitamin D (which you get from the sun) which can lead to death from a disease that deforms the bones of the skeleton and death. And so nature created baldness to increase the skin exposed to the sun so that there would not be a deficiency of the all-important vitamin D.
I believe that in the long run there is no such thing as redundant hereditary material that does not serve a function/purpose, but on the other hand I have no proof of this.
fresh,
I absolutely agree. It is important not to make the leap from ignorance to absolute certainty. But we do need to formulate some theory behind the idea. So unless you can think of why baldness is important to Europeans, but unimportant to Indians or Eskimos, it seems to me that the genetic material that causes baldness can be considered redundant.
To Roy
Another question arises. Does the fact that we cannot think about how a certain gene (for example, the baldness gene) increases the chances of survival and reproduction of the organism that carries it, necessarily mean that it does not increase these chances.
In other words, the fact that we think that certain hereditary material does not have a specific function or purpose does not mean that it really does not have a function/purpose. It may be that it has a function/purpose, only that we are too ignorant to know it.
fresh,
Even over time, genetic material may remain without a function or purpose (at least those that result in the survival of the individual, or his ability to produce offspring).
As an example of this (and in the last two answers I am already submitting an article on the evolution of man, which I am currently working on), if you look at four people of different origins: white Europeans, blacks from Africa, red-skinned people from America and Asians, you will find that there are clear differences between them. Indians, in general, have eagle noses, and Asians are on average shorter than whites. The whites, in turn, tend to go bald much more than the rest.
We know that the human groups diverged from each other 30 to 60 years ago, and it is likely that some traits made their way down the family tree, along with the original groups that inhabited the different living areas. From this it can be concluded that at least some of the useless features, such as baldness, have been preserved for a long time.
Roy, thanks for the reply.
And I want to refine my question. In a short period of time (which in evolutionary terms can also be several thousand years) I understand that there can indeed be genetic material without function or purpose. But in the long term is it possible for hereditary material to remain that does not serve a certain function? Because in short periods of time (short from an evolutionary point of view) the hereditary material is quite static and hardly changes, and in long periods of time it is already possible to notice that part of the hereditary material has been removed and another new part has been added.
fresh,
In some cases, a genetic mutation can spread in the population regardless of the benefit it brings.
As the simplest example, one can think of an island in the middle of the sea, with a population of mostly brown-eyed people. Now suppose there is an earthquake and a volcanic eruption one day, and only a man and a woman with blue eyes remain. When the island is repopulated, most of the offspring in the population will have blue eyes.
And of course, if they also have congenital mental retardation, then this too may definitely be inherited.
In order for a genetic mutation to spread in the population, it must be beneficial (such as resistance to a poisonous toxin for example) or it can be without any benefit or have no effect and still spread in the population.
[There is the matter of the JUNK DNA which apparently has no functional or phenotypic use, but today we know that it can return to function by another mutation that turns this JUNK DNA into an active gene that fulfills a certain function, so I do not refer to JUNK DNA this as useless genetic material these as dormant genetic material waiting for its opportunity to become active again]
the snake hisses