BIOLOGICAL ADAPTATION: CHARACTERISTICS, TYPES, EXAMPLES - BIOLOGY - 2025

A biological adaptation is a characteristic present in an organism that increases its capacity for survival and reproduction, in relation to its companions who do not have this trait. The only process that leads to adaptations is natural selection.

If we stop to look at the different lineages of living organisms, we will find that they are replete with a series of complex adaptations. From the mimicry of butterflies to the complex structure of their wings that allow flight.

Source: By Punnett, Reginald Crundall, via Wikimedia Commons

Not all the characteristics or traits that we observe in certain organisms can be immediately labeled as adaptations. Some may be chemical or physical consequences, they may be traits produced by genetic drift or by an event called genetic hitchhiking.

The characteristics of organisms can be studied by applying the scientific method to verify if they are indeed adaptations and what is their tentative function.

To do so, hypotheses about potential use must be proposed and tested with a suitable experimental design - either by manipulating the individual or by simple observation.

Although adaptations often seem perfect and even "designed", they are not. The adaptations were not the result of a conscious process since evolution has neither an end nor a goal, and neither does it seek to perfect organisms.

characteristics

Depending on the island, a different species of finch evolved.

An adaptation is a trait that increases the fitness of an individual. In evolutionary biology, the term fitness or biological fitness refers to the ability of an organism to leave offspring. If a certain individual leaves more offspring than a partner, it is said that he has greater fitness.

The most fit individual is not the strongest, nor the fastest, nor the greatest. It is the one that survives, finds a mate and reproduces.

Some authors often add other elements in their definitions of adaptation. If we take into account the history of the lineage, we can define adaptation as a derived trait that evolved in response to a certain selective agent. This definition compares the effects of character on fitness for a specific variant.

Types of adaptation

The three basic types of adaptations, based on how genetic changes are expressed, are structural, physiological, and behavioral adjustments. Within each of these types, different processes are carried out. Most organisms have combinations of all three.

Morphological and structural

These adaptations can be anatomical, including mimicry and cryptic coloration.

For its part, mimicry refers to the external similarity that some organisms are capable of developing to imitate characteristics of other more aggressive and dangerous ones in order to drive them away.

For example, coral snakes are poisonous. They can be recognized by their characteristic bright colors. On the other hand, queen mountain snakes are harmless, yet their colors make them look like a coral reef.

The appearance of an organism is modeled through structural adaptations depending on the environment in which it develops. For example, desert foxes have large ears for heat radiation and arctic foxes have small ears to retain body heat.

Thanks to the pigmentation of their fur, white polar bears camouflage themselves on ice floes and spotted jaguars in the spotted shade of the jungle.

Plants also suffer from these changes. Trees may have cork bark to protect them from wildfires.

Structural modifications affect organisms at different levels, from the knee joint to the presence of large flight muscles and sharp vision for predatory birds.

Physiological and functional

These types of adaptations involve the alteration of organs or tissues. They are a change in the functioning of the organism to solve a problem that occurs in the environment.

Depending on body chemistry and metabolism, physiological adaptations are usually not visibly displayed.

A clear example of this type of adaptation is hibernation. This is a sleepy or lethargic state that many warm-blooded animals go through in the winter. The physiological changes that occur during the hibernation period are very different depending on the species.

A physiological and functional adaptation would be, for example, the more efficient kidneys for desert animals such as camels, the compounds that prevent blood clotting in mosquito saliva or the presence of toxins in plant leaves to repel them. herbivores.

Laboratory studies that measure the content of blood, urine, and other body fluids, that trace metabolic pathways, or microscopic studies of an organism's tissues are often necessary to identify physiological adaptations.

It is sometimes difficult to detect them if there is no common ancestor or closely related species to compare the results with.

Ethological or behavioral

These adaptations affect the way living organisms act due to various causes such as ensuring reproduction or food, defending themselves against predators or changing habitats when environmental conditions are not suitable.

Among the behavioral adaptations we find migration, which refers to the periodic and massive mobilization of animals from their natural breeding areas to other habitats.

This displacement occurs before and after the breeding season. The curious thing about this process is that within it other changes develop that can be anatomical and physiological, as happens with butterflies, fish and butterflies.

Another behavior that is subject to change is courtship or courtship. Its variants can be incredibly complex. The objective of the animals is to obtain a mate and direct it to mating.

During the mating period, most species have different behaviors considered as rituals. These include exhibiting, making sounds, or offering gifts.

Thus, we can observe that bears hibernate to escape the cold, birds and whales migrate to warmer climates when it is winter, and desert animals are active at night during hot summer weather. These examples are behaviors that help animals survive.

Often times, behavioral adaptations take careful study from the field and laboratory to bring them to light. They usually involve physiological mechanisms.

These types of adaptations are also seen in humans. These employ cultural adaptations as a subset of behavioral adaptations. For example, where people living in a given environment learn ways to modify the food they need to cope with the given climate.

Are all features adaptations?

When observing any living being we will notice that it is full of characteristics that need an explanation. Consider a bird: the coloration of the plumage, the song, the shape of the legs and the beak, the complex courtship dances, can we all consider them adaptive characteristics?

No. While it is true that the natural world is full of adaptations, we should not immediately infer that the trait we observe is one of them. A trait may be present mainly for the following reasons:

They can be a chemical or physical consequence

Many traits are simply consequences of a chemical or physical event. The color of blood is red in mammals and no one thinks that the color red per se is an adaptation.

Blood is red due to its composition: red blood cells store a protein responsible for transporting oxygen called hemoglobin - which causes the characteristic coloration of said fluid.

May be a consequence of gene drift

Drift is a random process that produces changes in allele frequencies, and leads to the fixation or elimination of certain alleles in a stochastic way. These characteristics do not confer any advantage and do not increase the fitness of the individual.

Suppose we have a population of white bears and black bears of the same species. At some point, the study population suffers a decrease in the number of organisms due to an environmental catastrophe and most white individuals die by chance.

With the passage of time, there is a high possibility that the allele that codes for black fur will be fixed and the entire population will be made up of black individuals.

However, it is not an adaptation because it does not confer any advantage on the individual who possesses it. Note that the processes of gene drift do not lead to the formation of adaptations, this only occurs through the mechanism of natural selection.

It may be correlated with another characteristic

Our genes are side by side and can combine in different ways in a process called recombination. In some cases, genes are linked and inherited together.

To exemplify this situation, we will use a hypothetical case: the genes that code for blue eyes are linked to those for blonde hair. Logically it is a simplification, there are probably other factors involved in the coloring of the structures, however we use it as a didactic example.

Suppose that the blond hair of our hypothetical organism gives it some advantage: camouflage, protection against radiation, against cold, etc. Individuals with blond hair will have more children than their peers who do not have this characteristic.

The offspring, in addition to blonde hair, will have blue eyes because the genes are linked. Throughout the generations we can observe that blue eyes increase in frequency even though they do not confer any adaptive advantage. This phenomenon is known in the literature as “genetic hitchhiking”.

May be a consequence of phylogenetic history

Some characters may be a consequence of phylogenetic history. The sutures of the skull in mammals contribute to and facilitate the birthing process, and can be interpreted as an adaptation for it. However, the trait is representative in other lineages and is an ancestral trait.

Pre-adaptations and exaptations

Over the years, evolutionary biologists have enriched the terminology regarding the characteristics of the organism, including new concepts such as "pre-adaptation" and "exaptation."

According to Futuyma (2005), a pre-adaptation is “a trait that fortuitously serves a new function”.

For example, the strong beaks of some birds may have been selected to consume a certain type of food. But in appropriate cases, this structure can also serve as an adaptation to attack sheep. This sudden change in function is pre-adaptation.

In 1982, Gould and Vrba introduced the concept of "exaptation" to describe a pre-adaptation that has been co-opted for a new use.

For example, the feathers of swimming birds were not shaped by natural selection under the selective pressure of swimming, but fortuitously they served to do so.

As an analogy to this process we have our nose, although it was surely selected because it added some advantage in the breathing process, now we use it to hold our glasses.

The most famous example of exaptation is the panda's thumb. This species feeds specifically on bamboo and to manipulate it they use a “sixth thumb” derived from the growth of other structures.

Examples of adaptations

Flight in vertebrates

Birds, bats, and the now extinct pterosaurs convergently acquired their means of locomotion: flight. Various aspects of the morphology and physiology of these animals appear to be adaptations that increase or favor the ability to fly.

The bones have cavities that make them light, but resistant structures. This conformation is known as pneumatized bones. In today's flying lineages - birds and bats - the digestive system also has certain peculiarities.

The intestines are much shorter, compared to flightless animals of similar size, probably to reduce weight during flight. Thus, the reduction in the nutrient absorption surface selected an increase in cellular absorption pathways.

Adaptations in birds go down to molecular levels. It has been proposed that the size of the genome has been reduced as an adaptation for flight, reducing the metabolic costs associated with having a large genome, and therefore large cells.

Echolocation in bats

Source: By Shung, from Wikimedia Commons

In bats there is a particular adaptation that allows them to orient themselves spatially while they move: echolocation.

This system consists of the emission of sounds (humans are not capable of perceiving them) that bounce off objects and the bat is capable of perceiving and translating them. Likewise, the morphology of the ears of certain species is considered an adaptation to be able to receive the waves effectively.

The long neck of giraffes

Source: By John Storr, from Wikimedia Commons

No one would doubt that giraffes have an unusual morphology: an elongated neck that supports a small head and long legs that support their weight. This design makes different activities in the animal's life difficult, such as drinking water from a pond.

The explanation for the long necks of these African species has been a favorite example of evolutionary biologists for decades. Before Charles Darwin conceived the theory of natural selection, the French naturalist Jean-Baptiste Lamarck already wielded a concept - albeit erroneous - of changes and biological evolution.

For Lamarck, the neck of the giraffes was elongated because these animals constantly stretched it to be able to reach the acacia buds. This action would translate into an inheritable change.

In the light of modern evolutionary biology, the use and disuse of characters is considered to have no effect on offspring. The adaptation of the long neck must have arisen because the individuals that carried mutations for said characteristics left more offspring than their peers with shorter necks.

Intuitively we can assume that the long neck helps giraffes to get food. However, these animals usually forage for food in low bushes.

So what is giraffe necks for?

In 1996, researchers Simmons and Scheepers studied the social relationships of this group and disproved the interpretation of how giraffes got their necks.

For these biologists, the neck evolved as a "weapon" that males use in combat to get females, and not to get food in high areas. Various facts support this hypothesis: the necks of males are much longer and heavier than those of females.

We can conclude that, even if an adaptation has an apparently obvious meaning, we must question the interpretations and test all possible hypotheses using the scientific method.

Differences with evolution

Both concepts, evolution and adaptation are not contradictory. Evolution can occur through the mechanism of natural selection and this generates adaptations. It is necessary to emphasize that the only mechanism that produces adaptations is natural selection.

There is another process, called gene drift (mentioned in the previous section), which can lead to the evolution of a population but does not produce adaptations.

Confusions about adaptations

Although adaptations appear to be features designed exactly for their use, evolution, and consequently the conception of adaptations, do not have a goal or conscious purpose. Nor are they synonymous with progress.

Just as the process of erosion is not intended to create beautiful mountains, evolution is not intended to create organisms perfectly adapted to their environment.

Organisms do not strive to evolve, so natural selection does not give an individual what he needs. For example, let's imagine a series of rabbits that, due to environmental changes, have to endure a severe frost. The need of animals for abundant fur will not make it appear and spread in the population.

In contrast, some random mutation in the genetic material of the rabbit may generate a more abundant coat, making its carrier have more children. These children probably inherit their father's fur. Thus, abundant fur can increase its frequency in the rabbit population and at no time was the rabbit aware of this.

Also, selection does not produce perfect structures. They just need to be "good" enough to be able to pass on to the next generation.

References

1. Caviedes-Vidal, E., McWhorter, TJ, Lavin, SR, Chediack, JG, Tracy, CR, & Karasov, WH (2007). The digestive adaptation of flying vertebrates: high intestinal paracellular absorption compensates for smaller guts. Proceedings of the National Academy of Sciences, 104 (48), 19132-19137.
2. Freeman, S., & Herron, JC (2002). Evolutionary analysis. Prentice Hall.
3. Futuyma, DJ (2005). Evolution. Sinauer.
4. Gould, SJ, & Vrba, ES (1982). Exaptation-a missing term in the science of form. Paleobiology, 8 (1), 4-15.
5. Organ, CL, Shedlock, AM, Meade, A., Pagel, M., & Edwards, SV (2007). Origin of avian genome size and structure in non-avian dinosaurs. Nature, 446 (7132), 180.