What are inherited and acquired traits
Is it possible to inherit acquired traits?
"Spectacular, spectacular / No words in the vernacular / Can describe this great event / You’ll be dumb with wonderment." This is how a song in the musical Moulin Rouge begins. In terms of vaudeville, science is a chilled affair. But science also needs an audience, because that pays anyway. It should and wants to be enthusiastic. Then there is science journalism, which brings a little variety into dry matter.
There's nothing wrong with that. But there are exaggerations: some supposed bangers turn out to be Larifari on closer inspection. But who can do that: take a closer look? Who has the specialist knowledge to distinguish the justifiable exaggerations from the objectively unjustified? We are all laypeople in any number of fields and can therefore be seduced.
But even the generally trained common sense finds ways to separate the wheat from the chaff. And that is the way we are dealing with here. I pick out a headline in Bild der Wissenschaft magazine: “The Resurrection of Monsieur Lamarck. Organisms can inherit acquired properties ”(3/2011, p. 36 ff.). And the text of the article leaves no room for doubt: This is not about lower living beings, but about higher animals and humans. In the Spiegel article “The Memory of the Body” (DER SPIEGEL 32/2010, pp. 110-121) it reads, carefully packaged in question form, like this: “And if that weren't the sensational proof of a kind of unthinkable until then Inheritance - do genes learn from experience? "
If there is something to it, then it is actually spectacular, a real blast. For over a hundred years it has been burned in by biologists: “Since the offspring emerge from the germ cells, changes in the somatic cells of the animal have no influence on the genetic makeup of the offspring. Changes in genes, mutations, are only inherited if they occur in the germ lines. So there is no inheritance of acquired characteristics. ”(Christiane Nüsslein-Volhard in“ Das Werden des Lebens ”, p. 38)
Evolution is therefore based on trial and error; and the impetus for this is provided by chance alone. We cannot pass on what we have learned to our children in a biological, i.e. effortless, way. It can only be done culturally and more or less painfully through education and learning. That is the teaching recognized so far.
What is meant by “inheritance of acquired traits”?
The Bild der Wissenschaft article is about a chain of effects, as shown in the following graphic.
We do not need to doubt the building blocks of this graphic: Apparently we can learn, i.e. acquire qualities such as arithmetic and writing. The epigenetic modification of the genetic material was also demonstrated in the laboratories: Due to the material environment of the genes, certain switches are thrown that suppress or promote the interpretation of certain information contained in the genes. Since the material environment of the genes, i.e. first and foremost the cell content, also depends on external influences, it is at least plausible that the epigenetic changes can also be initiated from outside. It also seems that epigenetic traits can be inherited today. And that these inherited genetic characteristics can somehow make themselves noticeable again in living beings is probably not further disputed.
The claim in the article looks like this: There are examples that the entire chain of effects is run through and that finally the acquired property X and the expression Z are the same in the offspring: Z = X. This is exactly how one must understand the statement about the inheritance of acquired traits: The trait X is learned from an individual and passed on to offspring.
But what do we find in the article: The examples only concern a few sections of the chain of effects. The entire chain of effects is never run through. Non-existent connecting links are short-circuited, so to speak. And so the compelling force of the argument is missing. The first six examples are from the Bild der Wissenschaft article and the last two are from the Spiegel article, which has already been mentioned. So first the examples from Bild der Wissenschaft.
1. "By permanently reprogramming certain brain cells, early childhood trauma can make a person susceptible to depression later in life, for example."
2. "Or overeating in the womb can change metabolic cells in such a way that people are more prone to Ty-2 diabetes in old age."
3. It was discovered that “some patients with Prader-Willi syndrome - a severe developmental disorder - have inherited a natural epigenetic change from the paternal grandmother, which is normally overwritten by the father's germ cells”.
4. “If [fathers and grandfathers] had enough but little to eat before and during puberty, the sons and grandchildren grew older. If the fathers and grandfathers were able to feast, however, they passed a certain susceptibility to disease on to their descendants. "
5. It was discovered with a large survey that “it increases the risk of obesity in children if their fathers have smoked at the age of ten”.
6. “This picture fits the results of examinations from women whose mothers were pregnant with them during the Dutch starvation winter at the end of World War II. The extreme lack of food presumably changed the epigenetic program of the eggs that were just maturing. Because the children and even the grandchildren of these women are rather small and have an increased risk of certain diseases. "
Now come the examples from the Spiegel article.
7. “In experiments on laboratory rats, the Montreal team [Moshe Szyf and Michael Meaney] actually demonstrated that traumatic experiences can chemically mark the genetic material. To do this, they examined the gene for a receptor that breaks down stress hormones in the brain and helps you to process stress positively and to react calmly to stress. This beneficial gene was switched on in the brain cells of the rat pups being kept. The animals were therefore calm. In contrast, it was different with the neglected rats. The gene in question was more methylated - and thus switched off! "
8. “The stimulating environment acted like medicine on the shrunken brains. The animals then performed as well as healthy conspecifics in the learning test and were able to recall memory content normally. The remaining nerve cells had apparently succeeded in compensating for the loss of the dead neurons. The compensation was associated with epigenetic changes in the nerve cells of the hippocampus and the cerebral cortex. "
Comments on the examples
In Examples 1 and 2, inheritance does not play a role. It is all about the imprint of an individual.
Examples 3-6 are not about learning at all, but rather that a disorder Y with the epigenetic expression Z is captured and passed on: The first step in the chain of effects is missing. Instead of a subject there is some cause.
Example 7 is a counterexample for the inheritance of what has been learned. In a stress-free environment there is no incentive at all to strengthen stress resistance. And the stress resistance is apparently not inherited either, because that is not mentioned in the article.
Example 8 shows that the first two steps of the chain of effects are carried out: acquisition of skills X and the associated epigenetic modification of genetic material Y. But after that, the end is: the modification affects somatic cells that are outside the germline. Modification Y is not inherited.
What is learned may at times be hereditary. However, the articles cited here do not show this. If you look skeptically, nothing remains of the spectacular lead story.
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