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Natural Selection Examples


Antibiotic or insecticide resistance

The resistance of bacteria to antibiotics and insects to insecticides has increased greatly in recent years, and there is always a need to develop new antibiotics and new insecticides.

Take for example antibiotic resistance. For this, let's first imagine the existence of individuals adapted to a certain environmental condition. If we introduce a certain amount of antibiotic into this environment, there will be high bacterial mortality, but some that already have mutations that give them resistance to this substance will survive. These, in turn, when reproducing will give rise to individuals with characteristics distributed around another medium type.

If these individuals are given higher doses of this same antibiotic, again there will be high mortality and only those who already have the genetic conditions to resist higher doses of the drug will survive. By repeating the procedure, it will be possible to obtain populations with more and more individuals resistant to the antibiotic in question, which may lead to a shift of the average of the characteristics in the sense of greater resistance to a given substance.

Warning Coloring

Some animals produce or accumulate harmful chemicals and have flashy coloration, called warning coloration, signaling that they should not be ingested. Those who try to feed on one of these organisms learn not to eat a similar one.


The vibrantly colored coral snake and frog have a very dangerous poison.

An example is the monarch butterfly, which has a very showy orange and black color, being an animal easily visible in the environment. This species of butterfly produces substances that make them unpalatable to their predators. They learn to associate the coloring pattern with the unpleasant taste and avoid catching these butterflies.

Industrial Melanism

Prior to the industrialization of England, clear moths predominated; but sometimes dark, dominant mutants appeared, which, though more robust, were eliminated by predators because they were visible. After industrialization in the last century, dark mutants have been mimicked by soot. These became less predated because they were "hidden", which increased their frequency in the population. Moth predators, such as birds, act as selective agents.

Camouflage and mimicry

The action of natural selection is also verified in the establishment of characteristics that make organisms similar to others or objects of the environment, so that they go unnoticed by their predators or their prey.


False coral and true coral.

This is the case of certain animals that are less preyed because, by natural selection, they have a coloration that makes them imperceptible in the middle, combining their color pattern with that of the environment: bark, sand, twigs and leaves, for example.

On the other hand, certain predators may also have the medium color so that prey does not perceive their presence and is more easily captured.

In addition to color, certain animals also come to have by natural selection the shape and color of structures in the environment in which they live. This is the case of the insect leaf and stick insect, which resemble leaves and twigs respectively. These cases are called camouflage.


Leaf Bug and Stick Bug