Recent discoveries are prompting some researchers to argue that the synthetic theory of evolution needs to be updated. This article is an account of a meeting held at the Royal Society in London. Kevin Laland, an eminent evolutionary biologist from the University of St Andrews in Scotland, proposed to his prestigious colleagues nothing less than to renovate the theory of evolution. A muffled revolution, but with a tense climate of passions.
Kevin Laland looked through the meeting room to see about a hundred people who had gathered for a conference on the future of evolutionary biology. A colleague sitting next to him asked how things were going. Laland replied that it's going pretty well, we're not at the punch line yet.
Laland is an evolutionary biologist working at the University of St Andrews in Scotland. He's come to London to co-host a meeting at the Royal Society entitled New Trends in Evolutionary Biology. The meeting attracted mainly biologists, anthropologists, physicians, computer scientists and visionaries. Laland noted that the meeting room is being renovated and he hopes that the discussion will also bring about a kind of renovation on one of the most robust and fundamental theories of science.
In the mid-1900s, biologists updated Darwin's Theory of Evolution with new discoveries from genetics and other disciplines. The result is known as the synthetic theory of evolution that has guided evolutionary biology for nearly 50 years. But in the meantime, scientists have learned a lot about how life works. They can sequence entire genomes. They can observe the genes that turn on and off in developing embryos. They can observe how animals and plants respond to changes in the environment.
The result is that Laland and a group of biologists believe that the synthetic theory of evolution needs updating. It needs to give a new vision of Evolution and this update is known as theExtended Evolutionary Synthesis (Synthetic Theory and Extent of Evolution). Other biologists disagree that there is little evidence that such a change is necessary.
This meeting was the first public conference where Laland and his colleagues were able to present their visions. But Laland has no interest in preaching to those who already agree, so they have invited biologists who are very sceptical about the idea of this synthetic and extensive theory of Evolution. Both sides offered their arguments and one could feel a tension in the room with Tsss, TsssThere was a lot of applause and applause from the various speakers. But the fists are still in the pockets... for now.
Evolution as we know it
Science is constantly evolving, sometimes with revolutions taking place. Galileo and Newton took physics from its past mistakes in the 1600s and advanced it in small steps into the 1900s. Einstein and others laid the foundation for quantum physics, relativity and other ways of understanding the universe. It is stupid to say that Newton or others were wrong, but simply the fact that the universe is much more than moving matter.
Evolutionary biology has also had its own revolutions. The first was launched by Charles Darwin in 1859 in his book on the Origins of Species. Darwin gathered evidence from paleontology, embryology and other sciences to show that living things were related to each other by a common ancestor. Darwin also introduced a mechanism that causes long-term changes which is natural selection. Each generation of a species is full of variation. Some variation has allowed organisms to survive and reproduce and the characteristics are passed on to the next generation through heredity.
Darwin inspired biologists around the world to study animals and plants in a new way by interpreting their biology as adaptations that were produced over many generations. But Darwin succeeded despite completely ignoring the concept of a gene. It wasn't until the 1930s that geneticists and evolutionary biologists got together to rework the theory of evolution. Variations were caused by mutations that could produce new combinations. New species emerge when populations have mutations that no longer allow interbreeding.
In 1942, the British biologist Julian Huxley described this emerging framework in a book entitled Evolution: The Modern Synthesis. Today, scientists refer to this theory by the title of this book. Sometimes they use the term neo-darwinism, but that can be confusing. Neo-Darwinism emerged in the 1800s when biologists were proposing new ideas while Darwin was still alive.
The synthetic theory of evolution has become a powerful tool for asking questions about nature. Scientists have used it to make a large number of discoveries about life. For example, it has been understood why some people are more vulnerable to genetic disorders such as the sickle cell disease and why pesticides sooner or later failed to control pests. But as soon as the synthetic theory of evolution emerged, biologists began to criticize it for being too rigid. But it was not until the last few years that Laland and other researchers were able to organize themselves to formulate the broad synthetic theory of evolution.
These researchers do not consider the synthetic theory of evolution to be incorrect, but only that it does not capture the full richness of evolution. Organisms inherit more than genes. They can inherit other cell molecules as well as the behaviors they learn and the environments modified by their ancestors. Laland and his colleagues also challenge the concept that natural selection is the only explanation for the behaviour of life. Other processes can influence the course of evolution from development to the environments in which these organisms live. It's not just a question of adding more mechanisms, according to Laland, as this requires thinking about causality in a different way.
Additions to Darwin
Eva Jablonkaa biologist at Tel Aviv University, used his presentation to explore evidence of a form of heredity beyond genes. Our cells use a number of special molecules to control the genes that make proteins. In a process known as methylation, cells impose controls on their DNA to turn off certain genes. When cells divide, they can replicate the same controls on the new DNA. Certain signals from the environment can cause these cells to change these epigenetic controls that allow the body to adapt their behaviour to new challenges.
Some studies indicate that, under certain circumstances, an epigenetic change in a parent can be passed on to him or her. And these children can pass on this altered epigenetic profile to their children and it would be a heredity beyond the genes. The evidence for this effect is most robust in plants. In one study, researchers were able to track the altered patterns of methylation over 31 generations in a plant called Arabidopsis. And this type of heredity can make a considerable difference to the functioning of an organism.
In another studyIn a recent study, the researchers found that inherited methylation patterns can change the flowering time of theArabidopsis as well as the size of its roots. The variation in these patterns was greater than that caused by a normal mutation. After presenting this evidence, Jablonka believed that epigenetic differences could determine which organisms would survive long enough to reproduce. Natural selection could work in this system, she said.
Although natural selection is an important force in evolution, speakers presented evidence that it can be constrained or biased in a particular direction. Gerd Müller, a biologist from the University of Vienna, offered an example from his own research on lizards. A number of lizard species have evolved so that their feet no longer have toes. Some have four toes while others have only one toe and some have none at all.
Müller's synthetic theory of evolution has led scientists to view these changes as the product of natural selection that will favour one variant over others because that variant has a survival advantage. But this approach doesn't work if you're trying to understand the advantage of losing some of your toes. The answer is that there is no real selective advantage according to this researcher.
The key to understanding why lizards lose specific toes lies in the way lizard embryos develop their toes at the base. A tip appears on the side of the body and then five fingers emerge. But the toe will always have the same sequence. And when lizards lose their toes through evolution then they lose them in reverse order. Müller believes that this constraint is because not all mutations can create all the possible variations. Some combinations of toes are therefore out of bounds and natural selection will never select them.
Development can constrain evolution. But it also provides plants and animals with remarkable flexibility. Sonia Sultan, an evolutionary biologist from Wesleyan University, offered a spectacular case during her presentation by describing a plant she studies in the Polygonum family, better known as Renouée.
The synthetic theory of Sultan's Evolution would lead you to look at the adaptations of the Renouée as the highly refined product of natural selection. If the plant grows in a low sunny environment, then natural selection will favour the plant with genetic variances that allow them to adapt to this environment. For example, one variation is larger leaves to capture more photons. On the other hand, plants that grow in very sunny environments will adapt differently to these conditions. If you develop Renouées genetically modified under different conditions, then you'll have plants that behave so differently that it looks like they're different species.
The Renouées adapt the size of their leaves according to the sunlight they receive. In full sunlight, plants will have small, dense leaves, but in low light, these leaves will grow larger and thinner. On dry soil, these plants will send their roots deep into the ground to search for water, and on submerged soil, these plants will develop roots like tousled hair that will stay on the surface.
During the meeting, scientists felt that this flexibility, known as plasticity, can drive evolution. It allows plants to adapt to a number of habitats where natural selection will then adapt their genes. In another presentation, Susan Antón, a paleonantropologist at New York University, said that plasticity may have played an important role in human evolution that has not been noticed so far. This is because the synthetic theory of evolution has influenced the study of human evolution over the last fifty years.
Paleoantropologists tended to treat differences in fossils as the result of genetic differences. This allows them to draw an evolutionary tree of humans and their extinct relatives. This approach has many advantages according to Antón. Starting in the 1980s, scientists discovered that our oldest relatives were short with a small brain about 2 million years ago. Then a lineage grew tall and evolved to have larger brains. This transition marked the origin of our gender, the Homo.
But sometimes paleoantropologists find variations that are difficult to make sense of. Two fossils might look alike as if they were in the same species, but they are different in other ways. Scientists usually dismiss these variations as environmentally induced. We wanted to get rid of these things and go back to what Antón said they were like. But these things are too abundant to ignore. The scientists have found a considerable variety of fossils that resembled humans 1.5 million to 2.5 million years ago. Some were large while others were short. Some had large brains while others had small ones. They all have some Homo characteristics in their skeletons, but each has an assortment of mixes and matches.
Antón believes that the synthetic and extended theory of evolution could help scientists make sense of this deep mystery. In particular, she believes that these colleagues should seriously consider plasticity as an explanation for the strange diversity in early Homo fossils. In support of this idea, Antón pointed to the fact that present-day humans have their own plasticities. The quality of the food a woman eats while pregnant can influence the size and health of her child and these influences can last until adulthood. In addition, a woman's height, influenced in part by her mother's diet, can influence her own child. Biologists have found that women with long legs tend to have larger children.
Antón proposed that the strange variations in fossils could be dramatic examples of plasticity. All these fossils date from the time when the climate of Africa went through several changes. Droughts and heavy rains may have changed the food chain in different parts of the world, causing differences in the development of the first Homo. The synthetic and extensive theory of evolution could also give meaning to another chapter of our history, which is the appearance of agriculture. In Asia, Africa and the Americas, people domesticated seeds and livestock. Melinda Zeder, an archaeologist from the Smithsonian Institution, presented the problems of this transformation.
Before people started farming, they gathered and hunted their food. Zeder explained how many scientists treated the behavior of gatherers according to the synthetic theory of evolution. This behaviour was promoted by natural selection to get the best yield in their search for food. The problem is to determine how a gatherer will become a farmer. You don't get the same reward as taking food and eating it directly according to Zeder.
Some researchers suggest that the shift to agriculture may have been caused by a change in climate where it became difficult to find plants. But Zeder and other researchers have found no evidence of such a crisis. Zeder believes there is a better way to think about this transition. Humans are not passive zombies trying to survive in a fixed environment. They are creative thinkers who can change that environment. And in the process, they can lead evolution in a new direction.
Scientists know this process as niche construction and many species can do it. The beaver is the best example; it cuts down trees and creates dams. In this new environment, some species of plants and animals will do better than others. And they will find new ways to adapt to their environment. This is true for the plants and animals that live next to the beaver pond, but it is also true for the beaver.
For Zeder, it was a revelation when she learned about the niche-building phenomenon. The archaeological evidence she and other researchers have collected gives meaning to how humans have changed their environment. Early gatherers show signs where they moved plants in the wild to be closer to their habitat. And when they watered and protected the plants from herbivores, the herbivores adapted to their new environment. Weeds began to produce seeds. And some animals also adapted to become cats, dogs and other domesticated species.
Over time, the environment has changed from a sparse area of wild plants to dense fields. This environment has not only caused the evolution of plants, it has also caused the cultural evolution of farmers. Instead of remaining nomads, they gathered in villages so that they could work on the surrounding land. Society became more stable because the children received an ecological heritage from their parents and civilization began.
Niche construction is one of the many concepts proposed by the synthetic and extended theory of Evolution that gives meaning to domestication. Zeder gave several presentations ranging from early farmers to plant evolution. It sounded like a good publicity campaign for the synthetic and extended theory of evolution.
The return to natural selection
Among the members of the hearing was a biologist named David Shuker. After listening to the speeches for a day and a half, this researcher from the University of St Andrews was fed up. At the end of one speech, he raised his hand. The speech in question was given by Denis Noble, a physiologist who spent most of his career at Oxford. He said that he started as a "traditional" biologist, looking at genes as the ultimate cause of all processes in the body. But in recent years, he has changed his mind. He spoke of the genome as a sentient organ rather than a blueprint for life. This sensitive organ could detect stress and adapt to meet challenges.
To illustrate his vision, Noble discussed some experiences. One of them, published in 2015 by a team from the University of Reading, showed a bacterium that could swim by spinning its long tails. First, the scientists cut a gene from the bacterium's DNA that is essential for building tails. The researchers then put this tailless bacterium in a Petri dish with a small amount of food. The bacterium quickly consumed the food in its vicinity. If it couldn't move, then it would die. Within four days under these harsh conditions, the bacteria could swim again. Further analysis showed that the bacteria could develop new tails. This strategy produces a rapid evolutionary change in response to a hostile environment. It is a self-contained system that activates a particular characteristic that is triggered independently of the DNA.
Shuker didn't like that explanation. After Noble's speech, he asked for an explanation of the mechanism behind this discovery. Noble stammered in response, saying that the general mechanism is about networks, regulation and a desperate search for a solution to a crisis. « I advise you to read our paper " Noble replied.
As Noble struggled to respond, Shuker went to the paper on his tablet. And he read the abstract of the paper aloud. « Our results show that natural selection can quickly reconnect control networks. "And so, it's a good example of neo-Darwinian evolution... "he concluded in an ironic tone.
Shuker's intervention reflected the general sentiment of many skeptics in the conference. The paradigm shift proposed by the synthetic and extended theory of Evolution was unjustified in the view of many skeptics. And some even took the floor.
" I think I represent the Jurassic view of evolution... "said Douglas Futuyma. Futuyma is a biologist at Stony Brook University and author of a major book on evolution. In other words, he was the target of many complaints that the books did not give much importance to epigenetics and plasticity. Futuyma demonstrated why these concepts were ignored.
We must recognize that the main aspects of the synthetic theory of evolution are robust and well proven. Moreover, the biological principles discussed during the conference are not new. The architects of the synthetic theory of evolution were already discussing them 50 years ago. And there is a lot of research in this theory to give meaning to this concept.
Let's take the example of plasticity. Genetic variation in an animal or plant governs the range of shapes in which that organism will develop. Mutations can alter this range. And the mathematical models of natural selection show how it can favour some plasticities over others. But if the synthetic and extensive theory of evolution is so superfluous, then why is it getting attention to justify a lecture at the Royal Society? Futuyma suggested that the attraction is purely emotional rather than scientific. This theory allows life to be an active force rather than a vehicle for passive mutations. « I think that when we find it aesthetically or emotionally pleasing, then it's not the basis of the science "according to Futuyma.
But he added that the kind of research described during the meeting could provide interesting insights into the evolution. But these insights would require a lot of work and data. We need to stop with essays and position papers. Some members harangued Futuyma while other skeptical speakers were exasperated by these arguments that made no sense.
But the meeting was able to end after three days without a fist fight.
According to Laland, this is the first of many meetings to come. In September 2016, a consortium of scientists in Europe and the United States received $11 million in funding to launch 22 studies on the synthetic and extended theory of evolution. Many of these studies will test predictions that have emerged from the theory in recent years. They will determine whether species that build their own environments can transform into species that do not. These studies will also analyze whether plasticity allows species to adapt to new environments. Our critics tell us to provide evidence and that's what we're going to do, according to Laland.
Carl Zimmer, chroniqueur scientifique pour le New York Times. Il écrit également pour des magazines tels que National Geographic, Scientific American et The Atlantic. Traduction de son article publié dans Quanta Magazine.