Evolution
Without evolution there is no life
"Nothing in biology makes sense except when viewed in the light of evolution." This is the famous title of a 1973 article by Theodosius Dobzhansky, in which the Russian-American evolutionary biologist describes evolution as the means by which God created life on earth. But what exactly is evolution?
In biology, evolution is defined as the gradual change in heritable traits from one generation to the next. So, for example, when a species of rhinoceros that was originally hairless develops a protective coat during an ice age, that is evolution.
Even though new variants of the coronavirus are constantly emerging, this is also referred to as evolution. Evolution occurs only when there is selection among the traits of a group of organisms. In this process, also known as natural selection, traits are passed on to the next generation with varying frequencies: some become more common, while others become less common or disappear.
Selection
Selection is thus the driving force behind evolution. For selection to occur, the following conditions must be met:
- A trait must exist in different variants.
- The trait must be heritable.
- Different expressions of the trait must lead to differences in fitness.
The British naturalists Charles Darwin and Alfred Wallace discovered these fundamental principles of evolution. These principles explain the immense diversity of life on Earth: Individuals with different traits compete with one another for scarce resources and pass their characteristics on to their offspring. As a result, individuals continuously adapt to new environmental conditions, giving rise to a wide variety of forms and survival strategies.
An astonishingly simple principle for a phenomenon as incredibly diverse as life!
Evolution—Just a Theory?
When researchers draw conclusions based on their investigations, these are called hypotheses or theories. However, the “theory of evolution” is not a purely hypothetical assumption; rather, it has been based on measurements and observations from the very beginning. Today, evolution can also be replicated and studied in the laboratory. The fact that life on Earth has developed according to the principles of evolution is now a scientifically accepted fact.
Organisms on Earth pass on their traits through their genetic material. An individual’s DNA stores all the information necessary for its functioning. In addition, there are chemical changes to the DNA molecule. Thanks to these so-called epigenetic changes, an organism can also pass on traits it has acquired over the course of its life to its offspring.
For evolution to occur, therefore, the genome and/or the epigenome must be altered. Such changes are called mutations. Changes to DNA arise more or less randomly due to environmental influences such as radiation or mutagenic substances. Even when cells divide and duplicate their DNA in order to distribute it to their daughter cells, copying errors can occur, thereby giving rise to new variants for evolution.
Max Planck researchers have discovered that certain DNA regions are better protected against mutations and why this is the case. The cells’ repair machinery thus safeguards particularly important genes from potentially harmful changes. This finding contradicts the previously prevailing dogma that mutations do not occur with the same frequency in more important and less important genes—that is, they are not evenly distributed.
Prepared for Future Changes
Another dogma of evolutionary biology held that evolution proceeds in an undirected manner: Within a population, different expressions of a trait exist, from which natural selection chooses the variant that is optimal under the given conditions. According to this view, evolution does not act with foresight and has no goal.
Research findings from the Max Planck Institute for Evolutionary Biology are also challenging this dogma. In laboratory experiments, bacteria that had to adapt to regularly changing conditions developed genes that mutate up to 10,000 times faster than normal. This allows the cells to switch rapidly back and forth between several traits. In a sense, they are thus prepared for future changes.
From Beginning to End
Evolution has been taking place on Earth ever since, several billion years ago, the first molecules capable of reproduction emerged—molecules that could pass on their characteristics and variations to the next generation. Many researchers today believe that RNA molecules were the first to replicate and multiply on their own. How the first cells then arose remains unknown. Tiny fat droplets, which provided the RNA molecules with a protected reaction space, may have played a role in this process. Hot springs or freshwater pools may have offered suitable environmental conditions for this on the early Earth.
Through a continuous series of evolutionary steps over millions of years, life has adapted to different environmental conditions and expanded into new habitats. This is how the Earth’s biodiversity—comprising up to ten million animal and plant species—came into being. In a sense, this diversity can only be explained in this way. So one could also say: Evolution is life—and life is evolution!
Progress isn’t always as slow as a snail
Evolution continues to this day. In many cases, it proceeds so slowly that we don’t notice its effects within a single human lifetime. Some changes, however, take place within just a few years. Organisms with short generation times, in particular, can adapt relatively quickly to new environmental conditions.
One example is the house mouse. After the last ice age, the species split into a western and an eastern subspecies. Since then, the two lineages have diverged to the point where they are genetically distinct. However, the differences are not yet so great that members of the two lineages cannot interbreed. Researchers at the Max Planck Institute for Evolutionary Biology in Plön are taking advantage of this to study key evolutionary processes based on these differences.
Bacteria have even shorter generation times than mice. Some of these microbes produce several generations per day. As a result, evolutionary changes can be observed after just a few months. Bacteria are therefore an ideal model system for observing evolution live in the laboratory. And not only that—it can even be controlled. By altering the living conditions in the culture vessels, researchers can steer the bacteria’s development in different directions. Scientists at the Max Planck Institute for Evolutionary Biology have thus discovered how the bacterium Pseudomonas tolaasii can aggregate into cell clusters. In doing so, they have identified a possible pathway from unicellularity to multicellularity.
Evolution Relies on the Tried and True
The findings of Max Planck scientists and other research groups also show that evolution is often very conservative. It draws on existing genes and assigns them new functions. This also explains why organisms as diverse as nematodes and fruit flies possess so many genes that we humans also carry. The repurposing of genes is a central principle of evolution, and the environment plays a decisive role in this process.