Is Evolution just a Theory?!!

Many people still believe evolution just to be a theory! Are they right? And if not why?

What is evolution? The term evolution comes from a Latin word ‘evolutio’ meaning the act of unrolling (of a book) and has been used to describe gradual changes in opposition to revolution which stands for sudden changes. So what does mean evolution applied to living beings (or in biology)? It means that over generations every living beings are gradually changing and this is a fact. Indeed, in this sense evolution cannot be considered as just a theory, as we have observed repeatedly this phenomena since a long long time. I would say since the invention of agriculture, as humans realized by breeding certain individuals you can create breeds for specific needs. For example, humans have bred cows in order to either increase milk or meat production to such extant that nowadays we have 100s of distinct cow breeds that can be very dissimilar from each other. And this is not the sole example, look at dogs and the highly different races of dogs that human have selected for.

So here, usually, the reply to that (from a creationist) is that he does not deny it, but he cannot believe that a cow can become a horse or that species can give rise to another. I will reply to that:

• A cow cannot become a horse and a chimpanzee cannot become a human. They are different species and even after millions of years chimpanzees will not give raise to humans. However at one point in the past, a species has diverged and gave rise to the ancestors of humans and chimpanzees.
• What do you call a species? A species, even among biologists, has many different definitions and one can write a 1 000 pages book about it. Like every terms defined by humans, the meaning of species has evolved, since we found out exceptions from the original definition and then came up with another definition to bring it closer to what was observed. Just remember that all the terms we used have been defined by us to categorize things in order to ease our understanding but they are never set in stone. So usually, we call a species a group of individuals that can reproduce and give birth to viable and fertile individuals. This separation of groups reproducing between each other is not necessarily due to physiological incompatibility (impossibility to produce offspring despite reproduction) but also due to geographical, spatial, or temporal separation. An example would be if two groups of individuals (of the same species) are separated by an impassable mountain (or one group has its main activity in the morning and the other in the evening = temporal separation) over evolutionary times these 2 groups will become 2 different species. Accounting for that and coming back to our example of human selection, it is easily understandable that, let’s say, two races of dogs (Chihuahua & Great Dane) can be seen as 2 different species in Nature since they won’t be able to reproduce (if not chihuahuas would be the world champion of high jump 😉 !). So now imagine that instead 1000s years of human selection, you have millions of years of selection by Nature, it does not seem unreasonable any more that species can give birth to others.
• Then a typical reply to the point above would be, if you’re lucky (if not you will be called an heretic!!!): “Yes it seems fair, but the thing I do not believe is that random mutations can lead to change that are beneficial for an organism (from what I see it only leads to cancer) and in turn leads to new species”. To that I often reply: “Yes you are right, it seems kind of improbable, however look how diverse humans are, for example the eyes’ colour and this is the result of a gene mutation giving rise to another version of this gene (called allele). Over the course of time if this allele is beneficial for a given population then it is becoming predominant in this population. Then again over long period of time (millions or thousands of years), this small gradual changes (not only for one gene but several) along with the separation of populations can lead to the rise of different species. This has been observed in many populations where the generation time (period for producing offspring) is short, such as insects or unicellular organisms.”
• At this point you convinced most of the people, if not you will get such a remark: ” Even among scientists you are not agreeing that Darwinian selection (natural & sexual) can explain the rise of the actual biodiversity”. My reply would be: “Again you are right, but as an evolutionary biologist we do not rely only on Darwinian selection to explain all the processes underlying evolution, this is an 80 years old view. Other processes have been theorised and observed such as genetic drift or epigenetics (other factors than the genetic code, e.g. gene regulation, can be passed to the next generation, it can even be acquired during the life of an individual and be passed to its children). Moreover, we know now that it is not only simple mutations that can lead to changes but also more drastic changes in the DNA code with the effect of transposable elements for example (gene present in the genome that are capable of self-replicating and jumping in other parts of the genome, they are also called retroviruses). So yes, we do not know all about the mechanisms underlying evolutionary processes and there are still some difficulties to link micro-evolutionary mechanisms (e.g. changes of the genetic code or the regulation of genes) to macro-evolutionary mechanisms (e.g. speciation). But hey! that is why I have such a job!!! Everyday, I learn new things and try to improve our global understanding on how nature has produced such a biodiversity and that is the reason why I am so passionate about my job. Everyday, we know more and more about evolution and are refining our understanding of evolutionary processes but we don’t know everything, BUT IT DOES NOT MEAN THAT EVOLUTION IS JUST A THEORY!”

PS: this article has been written by B. Fouks and should be solely considered as an opinion. The statements, views and opinions expressed in this column are solely those of the author and do not necessarily represent those of the funding body (EU MSCA-IF) and the University (WWU).