Liberated evolution

Whether to arrange evolutionary biology a serious revision, or no "revolution" is expected?

When researchers from Amori University in Atlanta trained the mice to scare the smell of almonds (using electrical discharges), they were to their horror that both children and grandchildren of these mice were also afraid of the smell of almonds. But this should not be. Many generations of schoolchildren have been told that inheriting acquired properties is impossible. A mouse cannot be born with the knowledge gained by its parents — it is as if a mouse that lost its tail during an accident would give birth to a tailless mouse.

There is nothing shameful in not knowing about the state of modern evolutionary biology, unless of course you are a biologist. It dates back to the synthesis of science, which arose in the years 1940-60, married the mechanism of natural selection , discovered by Charles Darwin , with the discovery of gene inheritance by Gregor Mendel . The traditional, still dominant approach suggests that adaptation - everything from the human brain to the peacock's tail - is fully and satisfactorily explained by natural selection (and subsequent inheritance). However, with the advent of new ideas from genomics , epigenetics and developmental biology, most evolutionists agree that their field of knowledge is changing. A lot of data suggests that the process of evolution is much more complicated than it used to be.

Many specialists in evolutionary biology , including myself, call for expanding the description of the theory of evolution to the so-called “extended evolutionary synthesis” (RES) [ extended evolutionary synthesis , EES)]. The main question is whether what happens to organisms during their life — their development — is an important and previously unforeseen role in evolution. The orthodox opinion said that the development process for the most part is not related to evolution, but the views of the RECs consider it to be the most important. Authoritative and eminent supporters of both approaches are gathered from both sides of the dispute; major professors from Ivy League universities and members of state academies face their heads over the mechanisms of evolution. Some people even begin to suspect that revolution is brewing in this area.

In his book On Human Nature (1978), evolutionary biologist Edward Wilson stated that human culture is on a genetic leash. This metaphor was controversial for two reasons. First, as we shall see, it is equally true that culture holds genes on a leash. Secondly, if cultural learning is influenced by genetic propensities, few cultural differences can be explained by existing genetic differences.

However, this phrase can explain a lot. Imagine a person (genes) walking and trying to control a muscular mastiff (human culture). The trajectory of this couple (the path of evolution) reflects the result of their struggle. Now imagine that the same person is struggling with several dogs walking on leashes of different lengths, while each of the dogs pulls him in his own direction. These stifles depict the influence of developmental factors — epigenetics, antibodies, hormones transmitted by parents, as well as ecological and cultural heritage.
Among the flocks of dogs - epigenetic, cultural and environmental inheritance, as well as the influence of parents and brain plasticity

A person fighting with walking dogs is a good metaphor of how the REC describes the adaptation process. Does this require a revolution in evolution? To answer this question, you need to understand how science works. And here the authorities are not biologists, but philosophers and historians of science. The book The Structure of Scientific Revolutions (1962) by Thomas Kun popularized the idea that science is changing through revolution in understanding. It was believed that these "paradigm shifts" follow a crisis of confidence in the old theory, manifested during the accumulation of conflicting data.

Karl Popper is still there, and his hypothesis that scientific theories cannot be proved, but can be refuted, or falsified . Consider the hypothesis: "All the sheep are white." Popper argued that no amount of discoveries supporting this hypothesis can serve as proof of it, since it cannot be ruled out that in the future there will be contradictory evidence; and vice versa, the observation of a single black sheep will definitely refute this hypothesis. He argued that scientists should strive to perform decisive experiments that could potentially disprove their theory.

And although the ideas of Kuhn and Popper are well known, from the point of view of philosophers and historians, they remain controversial. The current state of these areas was best formulated by the Hungarian philosopher Imre Lakatos in his book Methodology of Scientific Research (1978):

The history of science refutes both Popper and Kuhn: on closer inspection, Popper’s criterion and Kuhn’s revolution turn out to be myths.

Popper's argument may seem logical, but it does not always correspond to how science works in the real world. Scientific observations are subject to measurement errors; scientists are people attached to their theories; scientific theory can be hellishly complex - because of this, the evaluation of scientific hypotheses is terribly confusing. Instead of accepting that our hypothesis might be wrong, we criticize the methodology (“This sheep is not black, you have the wrong tool”), argue about interpretation (“The sheep are just dirty”), invent corrections to the hypothesis (“I have to see domesticated sheep, not wild mouflons ”). Lakatos calls such corrections and props "auxiliary hypothesis"; scientists offer them in order to protect the "main" ideas so that they are not rejected.

Such behavior is clearly discernible in the scientific debate on evolution. Take the idea that new properties acquired by the body during life can be passed on to the next generation. This hypothesis was widely known at the beginning of the 19th century thanks to the French biologist Jean-Baptiste Lamarck, who used it to explain evolution. However, it has long been considered that it has been refuted experimentally - to such an extent that the term “Lamarkovsky” has a derogatory implication in evolutionary circles, and any researcher expressing sympathy for this idea, in fact, gets the stamp of “eccentric”. The wisdom acquired by parents cannot influence the characteristics of their offspring.

That's just really can. Gene expression , the phenotype of the organism — its real characteristics — is influenced by chemicals that join genes. Everything from diet to air pollution and parental behavior can affect the addition or removal of these chemical markers, which can turn genes on and off. Usually these so-called. “Epigenetic” additives are removed during the production of sperm and eggs, but it turns out that some of them escape the discharge into the original state and are passed on to the next generation along with the genes. This process is known as “epigenetic inheritance,” and more and more studies confirm its reality.

Let us return to the mice who feared almonds. The epigenetic label transmitted in semen allowed the mice to inherit fear. In 2011, another unusual study reported that worms react to contact with a virus, producing factors that drown out this virus — chemicals that disable it — but, interestingly, subsequent generations of worms epigenetically inherited these chemicals through regulatory molecules known as " small RNA ". Now there are hundreds of such studies ; many of them have been published in the most prestigious and well-known journals. Biologists argue whether the epigenetic inheritance is Lamarkian or whether it only reminds him , but one cannot get away from the fact of inheritance of acquired characteristics.

According to Popper's logic, the only experimental demonstration of epigenetic inheritance — that very single black sheep — should be enough to convince evolutionary biologists of the possibility of this. However, for the most part, evolutionary biologists did not run to change their theories. Instead, as Lakatos suggested, we came up with auxiliary hypotheses that allow us to maintain our long-standing viewpoint (that is, inheritance is due to gene transfer through generations). This includes ideas about the rarity of epigenetic inheritance, that it does not affect functionally important properties, that it is under the control of genetics, and that it is too unstable to support the propagation of properties through selection.

Unfortunately for traditionalists, these attempts to limit epigenetic inheritance do not look convincing. It is already known that epigenetics is very common in nature, and every day more and more examples appear. It affects functionally important properties, such as fruit size, flowering time and root growth in plants - and although only a small part of the epigenetic variants are adaptive, the same is true for genetic variants, therefore such grounds are hardly suitable for discarding this process. In some systems, where the rate of epigenetic changes was measured carefully, for example, the plant Rezuhovidka Tal (Arabidopsis thaliana), the rate was small enough for the selection to occur, leading to cumulative evolution. Mathematical models show that systems with epigenetic inheritance evolve in a different way than systems relying solely on genetic inheritance — for example, the selection of epigenetic markers can lead to changes in gene frequency. There is no longer any doubt that epigenetic inheritance forces us to change the approach to the study of evolution.

Epigenetics is only part of the story. From culture and society, we all inherit the knowledge and skills acquired by our parents. Evolutionary biologists accepted this fact at least a hundred years ago, but until recently it was thought that this applies only to humans. But this is not so straightforward : various creatures of the animal kingdom socially assimilate diet, technology of eating, avoiding predators, communication, migration, mating choices and breeding grounds. Hundreds of experimental studies have demonstrated the existence of social learning in mammals, birds, fish, and insects.

Among the most interesting data are studies on the cross-breeding of great tits and common azureas . When representatives of one species are grown by representatives of another, they change various aspects of behavior, becoming closer to the behavior of their adoptive parents (including the height of the trees where they feed, their choice of prey, method of feeding, call and song, and even the choice of partner for mating). Everyone assumed that the behavioral differences of the two species were genetic, but it turned out that many traditions are cultural.

In animals, culture can survive for a surprisingly long time. Archaeological remains show that chimpanzees used stone tools to open nuts for at least 4,300 years. However, for epigenetic inheritance, it would be wrong to assume that animal culture should exhibit stability similar to genetic, and be evolutionarily significant. In the process of a single mating season, features may be developed in qualities that individuals find attractive in their partners; this process was experimentally demonstrated for fruit flies, fish, birds and mammals, and mathematical models show that such “copying partner choice” can strongly influence sex selection.

Another illustration came from the field of bird singing. When young males learn their songs (usually from nearby males), they change the pressure of genes through natural selection, which affects how males acquire songs, and which songs females prefer. It is known that the cultural transmission of songs encourages the evolution of hatching parasitism - when birds, such as cuckoos, do not make their nests, but lay eggs to other birds - when some such parasitic birds rely on cultural training in the matter of choosing a partner. It also promotes speciation, since the preferences of certain “dialects” of songs help to maintain genetic differences in populations.

In the same way, culturally acquired knowledge of feeding in killer whales - when different groups specialize in different types of fish, fur seals or dolphins - leads to their division into several species. Of course, culture reaches the maximum capacity of our species - it is already well known that our cultural habits were the main reason for the natural selection that took place in our genes. The production of dairy products and the consumption of milk led to the selection of a genetic variant that increases the production of lactase (the enzyme necessary for digesting dairy products), and starchy agricultural diets contributed to an increase in amylase (the corresponding enzyme that breaks down starch).

All these difficulties cannot be reconciled with an exclusively genetic approach to adaptive evolution, as many biologists already recognize. They indicate that an evolutionary process in which the genomes (over hundreds and thousands of generations), epigenetic modifications and inherited cultural factors (over several, perhaps tens or hundreds of generations), and parental effects (over the course of a single generation) jointly point to features of adaptation of organisms. Such extragenetic types of inheritance give organisms the flexibility to quickly adjust to the environment, and entail genetic changes - just like a noisy pack of dogs.

Despite all these exciting new data, they are unlikely to launch a revolution in evolution, since science does not work that way - at least, the study of evolution. The Kunovo paradigm shift, like Popper’s critical experiments, is closer to myths than to reality. Study the history of evolutionary biology and you will not see anything resembling a revolution. Even the general adoption of the theory of evolution by Charles Darwin through natural selection took about 70 years from the scientific community, and at the turn of the 20th century they looked at it with great skepticism. Over the following decades, new ideas emerged, they were critically evaluated in the scientific community, and they gradually joined existing knowledge. For the most part, evolutionary biology has been updated without experiencing periods of particular “crisis”.

Also happening today. Epigenetic inheritance does not disprove genetic, but shows that it is only one of several mechanisms for inheriting properties. I do not know of any biologist who wants to break textbooks or throw away natural selection. The debate on evolutionary biology concerns whether we want to expand our understanding of the causes of evolution, and whether they change the way we look at the process as a whole. In this sense, "ordinary science" is just happening.

Why do traditionalists among evolutionary biologists complain about erring evolutionary radicalists agitating for a paradigm shift? Why do journalists write articles about scientists calling for a revolution in evolutionary biology? If no one needs a revolution, and scientific revolutions rarely occur anyway, what is all the fuss about? The answer to this question gives a very interesting understanding of sociology in evolutionary biology.

A revolution in evolution is a myth promoted by the unlikely alliance of conservative evolutionists, creationists, and the media. I have no doubt that there is a small number of sincere and revolutionary-minded radicals, but most of the researchers working in the direction of advanced evolutionary synthesis are simple workers of evolutionary biology.

Everyone knows that sensations sell newspapers well, and articles foreshadowing big upheavals are becoming popular. Creationists and supporters of “intelligent creation” feed this impression with the help of propaganda, exaggerating the difference of opinion among evolutionists and giving a false impression about the cataclysms taking place in the field of evolutionary biology. Even more surprising is how conservative biologists claim that their evolutionary colleagues go to war against them. To portray an opponent as an extremist and tell people how they are attacked - an old rhetorical tactic aimed at winning a dispute or acquiring adherents.

I have always associated such games with politics, not science, but now I understand that I was naive. Some of the behind-the-scenes machinations that I observed, intended to prevent the spread of new ideas by all means, simply shocked me and did not correspond at all to the practice in other fields of science known to me. Scientists also have careers and heritage at stake, as well as funding, influence and power. It bothers me that the traditionalist rhetoric gives the opposite results, leads to confusion and inadvertently fuels creationism, exaggerating the size of the differences. Too many respected scientists feel the need for changes in evolutionary biology, so that all of them can be swept aside as radicals.

If advanced evolutionary synthesis is not a call for revolution in evolution, then what is it and why do we need it? In order to answer these questions, one must recognize that Kuhn was right - namely, that in every scientific field there are shared ways of thinking, or "conceptual platforms." Evolutionary biology is not very different in this sense, and our shared values ​​and assumptions affect what data is collected, how it is interpreted, and what factors are involved in explaining the methods of evolution.

Therefore, science needs pluralism. Lakatos emphasized that alternative conceptual platforms — what he called various “research programs” —can be valuable in the sense that they encourage the introduction and testing of new hypotheses or lead to innovative ideas. This is the main function of RES - to feed and discover new areas of research and productive methods of thinking.

A good example is “developmental bias]. Imagine interesting cichlid fish from East Africa. For dozens, and possibly hundreds, of cichlid species from Lake Malawi, there are independently evolved “copies” of species in Lake Tanganyika - with surprisingly similar body shape and feeding method. This similarity is usually explained through convergent evolution: random genetic variants appeared as usual, but similar environmental conditions chose genes that led to equivalent results. The way organisms grow and develop may limit the properties that appear, but the variation itself is considered to be essentially random.

However, the extraordinary level of parallelism in the evolution in these two lakes suggests the possibility of additional factors. What if some fish production methods are more likely than others? What if a variation of properties leans towards certain solutions? Selection would still be included in the explanation, but parallel evolution would be more likely.

Molars in mammals provide some of the most convincing data for such distortion. Studies show that you can use a mathematical model based on laboratory mice to predict the size and number of teeth in 29 other rodent species. Instead of freely producing any shape or number of teeth, natural selection appears to lead the species along a very specific path created by developmental mechanisms. The existence of exceptions — such rodents as voles, with a different number of teeth — demonstrates that the old way of thinking (that developmental limitations affect selection) is not entirely correct. The impact of development is more subtle and more interesting: developmental mechanisms distort the landscape for selection and help determine which features should emerge.

Such studies are exciting, for they help evolutionary biology to become a more predictive science. Why did such ideas not receive so much attention until recently? We are returning to conceptual platforms. Historically, evolutionary biologists regarded the distortion of phenotype variations as “limiting” - an explanation of why evolution or adaptation did not occur. The way organisms grow limits the possibilities for acquiring or adapting. Traditionally-minded evolutionists said little about this, and did not accept the positive role of development as a cause of change and direction of evolution.

It took another point of view (in this case, evolutionary biology), for the emergence of motivation for such experiments. From the point of view of evolutionary biology, the distortion partially explains the evolution and adaptation that occurred. Rodents' teeth and fish bodies look like this, because the way these creatures grew increases the likelihood of such characteristics. Distortion becomes a more important concept in evolutionary explanations. Bringing this phenomenon to light, RES hopes that it will be investigated.

The RES, or at least the way we and our colleagues present it, is best viewed as an alternative research program for evolutionary biology. He was inspired by recent discoveries in evolutionary biology and related fields, and begins with the assumption that developmental processes play an important role as new (and potentially useful) variations of the phenotype, causes of differences in survivability of these options and causes of inheritance. In contrast to the way evolution was considered traditionally, in RES the burden of creativity in evolution bears not only natural selection. This alternative way of thinking is used to propose new hypotheses and new research programs. Пока ещё мы только в начале пути, но уже видны признаки того, что эти исследования начинают приносить плоды.

Если эволюцию не получится объяснить исключительно изменениями в частоте генов; если такие ранее отвергнутые механизмы, как наследование приобретённых характеристик, всё-таки окажутся важными; если эволюция всех организмов будет зависеть от развития, обучения и других видов пластичности – будет ли всё это означать появление радикально новой и очень глубокой оценки эволюции? Никто не знает: но с точки зрения нашего адаптирующегося человека, выгуливающего собак, эволюция меньше похожа на неторопливую генетическую прогулку и больше напоминает яростную схватку генов, пытающихся поспевать за жёстким процессом развития.

Кевин Лалэнд – профессор бихевиористской и эволюционной биологии в Университете св. Эндрюса в Шотландии, руководитель проекта исследовательской программы расширенного эволюционного синтеза. Его последняя книга называется «Незаконченная симфония Дарвина: как культура создала человеческий разум» (2017) [Darwin's Unfinished Symphony: How Culture Made the Human Mind].