Artificial selection: what it is, types, and how it works

Let's see what artificial selection is and how it has been used by humans for thousands of years.

The world is inhabited, approximately, by 7.7 billion inhabitants, of which (according to the World Health Organization) 690 million went hungry during 2019. It is a fact that global production and distribution of goods is completely skewed as, on the other side of the coin, 1.9 billion people were overweight in 2016.

Population numbers are soaring and, unfortunately, food production chains are increasingly threatened by multiple processes: multi-resistant bacteria, lack of space, climate change and many other deleterious events for livestock and agriculture. It is reasonable to think, therefore, that the "natural" characteristics of the beings we feed on are no longer sufficient.

This is where terms such as genetic engineering and artificial selection come into play.. Humans have modified or selected the genes of various species of living beings of agricultural or livestock interest or any animal of social interest (pets, pack animals, etc.) for their own benefit throughout history: we are not facing a new practice, but we are facing an increasingly aggressive expansion of it. If you want to know more about artificial selection and what it entails, read on.

What is artificial selection?

It is common for society to fear the "specter" of change, as playing god may seem dangerous in a world where we still have a lot to learn. The reality is that, for better or for worse, human beings have been moving away from natural mechanisms for hundreds and hundreds of years.

To understand what artificial selection is, the first thing to clarify is what it is not, since it is common to attribute biased characteristics to this type of term depending on the argument that is being made. With all the care in the world and lead feet, we confront you the term artificial selection with others related to it in the following lines.

Artificial selection VS natural selection

Natural selection is defined as the evolutionary mechanism based on the differential reproduction of genotypes in a Biological population.. Postulated by the famous biologist Charles Darwin, natural selection postulates that environmental conditions (whether biotic or abiotic, i.e., from the physical environment or caused by other living beings) favor or hinder the reproduction of species according to their peculiarities.

It is necessary to know that natural selection is not an infallible and perfect mechanism: living beings do what they can with what they have, which is why not all adaptations are the best in a given environment. To sum up, all this evolutionary force is based on fitnessThe living beings that present the fittest characteristics in a given environment will live longer and, therefore, will reproduce more and pass on their genes to the next generations.

It is also important to note that natural selection is not a unique force, since evolution is also biased by processes such as genetic drift, which are completely random and stochastic in nature.

On the other hand, artificial selection, as its name suggests, does not respond to normal adaptive mechanisms in a wild environment.. We are dealing with an environment that is anything but natural, since it is characterized by the fact that it develops in a largely anthropized environment where we, human beings, choose what we are interested in.

Artificial selection VS genetic engineering

It is very common to observe a clear confusion regarding these two terms. It is time to define them both quickly and concisely to leave no room for doubt.

Genetic engineering can be summarized in the following concept: a discipline that encompasses a series of techniques that involve the direct modification of an organism's genes for a specific purpose..

Artificial selection, on the other hand, is the selection of parents with one (or several) traits of interest, so that all possible descendants also present them and the desired trait spreads in the population.

It is shocking to learn that, to date, only 27 types of crops are commercialized, only 27 types of transgenic crops are marketed and 95% of genetically modified animals are laboratory rats for purely scientific purposes.. The reality is that most of the food that ends up on our table is the product of artificial selection and not of genetic engineering, since obtaining a transgenic animal is monetarily expensive, difficult and, to date, not a common practice in the livestock sector.

Types of artificial selection

As you may have noticed, there is a clear attribute that differentiates artificial selection from other mechanisms: here the human being chooses the best of what is already available, because he does not create new traits where there was no evidence of them before..

Thus, when we speak of a hen that lays a great many eggs, we are referring to the product of an extensive history of artificial selection where the most suitable laying parents have been selected each time, not of a transgenic animal that has undergone genetic modification. It is very important to make this distinction because, although the term "transgenic" is fashionable, it is not at all as widespread as many people think.

Once we have emerged from this forest of terminological doubts, it is also necessary to emphasize that there are several types of artificial selection. Based on the degree of planning, there are two types of artificial selection:

• Conscious: when it responds to a selection plan, designed and executed at will, to preserve certain traits over others in a domestic species.
• Unconscious: when it occurs accidentally, responding to criteria not planned in advance (or at least not formalized).

A clear example of conscious selection that is self-explanatory is that of dogs: breeds are the product of crossbreeding and inbreeding, where individuals of interest are selected for sexual reproduction by means of specific criteria. On the other hand, and without leaving the world of canids, the case of black wolves could be considered as an unconscious artificial selection.

According to scientific sources, these black wolves belong to the same species as the lifelong gray wolves (Canis lupus), but it is speculated that their melanistic color arose from crossbreeding with domestic dogs that had this gene. Thus, in this case, humans would be carrying out an unconscious artificial selection: the characteristics of an animal population are indirectly (and unintentionally) modified.

On the other hand, artificial selection can also be divided according to what is sought (or not) in the population of interest:

• Negative selection: to avoid the birth of specimens with undesirable characteristics.
• Positive selection: to favor the reproduction of certain living beings with the desired characteristics.

In our minds, we tend to think of positive selection when talking about artificial selection: we choose the biggest tomatoes, the hens that lay the most, the cows with the most meat and muscle. The reality is that, when a farmer slaughters an animal with a genetic dysfunction, he is already unwittingly making a negative artificial selection. It is much more common to select living beings based on what is not wanted (diseases, congenital defects and other events) than to select them for their positive attributes.

• You may be interested in, "What is the genetic code and how does it work?"

Benefits and detriments of this procedure

We cannot close this space without the obvious ethical connotations that artificial selection carries with it.. Among the clearest benefits of these techniques we can find the following:

• Artificial selection allows a more harmonious coexistence between domestic species and human society.
• Production capacity can be increased with the same space and number of individuals.
• Sometimes, artificial selection allows the permanence of certain species over time, since they are in a controlled environment.

On the other hand, the disadvantages of all this are also more than clear: sometimes some populations become a shadow of what they were in the wild. Excessive inbreeding, for example, leads to a weakening of the genetic lineage of the species and of its evolutionary destiny.The descendants of this type of selection are more prone to certain diseases, anatomical difficulties, unpredictable mutations and a host of other problems. The reality is truly uncomfortable, as it is clear that a pug dog will never have the same health and evolutionary fitness as a wolf.

And you, what do you think?

As you may have read in these lines, this is a very thorny issue. It is clear that artificial selection entails multiple ethical dilemmas, for when is it unjustifiable to modify a species? To what extent can the evolutionary rope be stretched without breaking it? What is the limit of animal suffering that we are willing to encourage in order to increase productivity?

All these questions depend on the judgment and values of each and every reader who has read these lines. There is no definitive answer, but one thing is clear: there are more and more people on the planet, and nature is no longer able to provide for us. What to do from here is subject to personal judgment.

Bibliographical references:

• With hunger on the rise and malnutrition persisting, achieving zero hunger by 2030 is doubtful, warns a report by the United Nations, World Health Organization. Retrieved December 13 from https://www.who.int/es/news/item/13-07-2020-as-more-go-hungry-and-malnutrition-persists-achieving-zero-hunger-by-2030-in-doubt-un-report-warns#:~:text=In%20the%20%C3%BAltimate%20edici%20C3%B3n%20of,60%20million%20in%20five%20a%20a%C3%B1os).
• Artificial selection, undestandingevolution. Retrieved December 13 from https://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_30_sp.
• Lungarete, F. (2012). Artificial selection (Doctoral dissertation, Universidad Nacional de La Plata).
• Soler, M. (2002). Evolución. Proyecto Sur de Ediciones: Granada.