In the first half of the 19th century, German scientists E. Haeckel and F. Müller carried out serious embryological and comparative anatomical studies that led to the creation of a biogenetic law and the development of ideas about analogies, homologies, atavisms and rudiments. This article will be devoted to the study of such a group of living organisms containing homologous organs. These are plant and animal objects widespread in the world, in which body parts have a common origin and a single structural plan, although they can differ greatly in appearance. What led to their appearance?
Causes of occurrence
Evolutionary processes occur in populations of living beings and underlie microevolution. The emergence of new species is possible due to the accumulation of increasing differences in organisms, affecting both their structure and functions. The process leading to a divergence of morphological and anatomical features, arising as an organism's response to changing environmental factors, is called divergence. Homologs are parts of the body in individuals that have undergone natural selection and formed as a result of adaptation to the conditions of their habitat. They are studied in detail in the course of zoology. Let's take a closer look at them.
Features of the structure of vertebrates
The forelimbs of all mammals consist of the same bones: the humerus, ulna, radius, carpal bones, metacarpus and phalanges of the fingers. But various environmental conditions with the course of evolution left imprints both on the shape of the skeleton of the forelimb and on its functions. It is enough to compare the appearance, shape and size of this part of the body, for example, in a giraffe, monkey or mole. It is divergence that underlies the appearance of such organs as homologues. This is confirmed by comparative anatomical studies not only among various groups of animals, but also in the plant world. Let's look at them in the next paragraph.
Modifications of vegetative organs
During ontogenesis, representatives of the world of flora not only acquire new features, but also modify parts of their body. In botany, this phenomenon is called the modification of vegetative parts and is considered as an adaptation that arose in the course of phylogenesis. You can observe it with representatives of the department of flowering plants. In them, this leads to the emergence of structures such as homologues. This is manifested in the form of an adaptive reaction of the body to environmental factors. It is known that the root system of all seed plants develops from the germinal root according to a single plan and performs functions common to all species:fixing in the soil, support, absorption and conduction of water and solutions of mineral substances. However, the appearance of the roots can change greatly if they begin to perform special functions. Thus, the stilted roots of a pandanus growing in tropical swamps are homologous.
They keep the bottom of the stem completely submerged in water, preventing it from rotting. In orchids, aerial roots are homologous to the underground organ - they are involved in extracting additional volumes of air for the plant to breathe. They serve as a reservoir that accumulates starch and other organic compounds, beet and carrot roots, Jerusalem artichoke and dahlia root tubers. All of these modifications are homologues. Biology claims this with good reason, since they correspond to each other and to the general principle of the structure of the underground organ - the root.
Homologies in the human body
Representatives of the class of vertebrates, which includes Homo sapiens, have a single structural plan for the musculoskeletal system, in particular, its axial part - the spine.
But a person has features that have arisen as an adaptation to upright posture, for example, the shape of the spine resembles the Latin letter S. In addition, in the skeleton of the upper limb, consisting of the same bones as in animals, the phalanx of the thumb is opposed the remaining four fingers, which is the result of the ability to work. Homologs are all named examples that have arisen in the process of anthropogenesis.
