In the first half of the 19th century, German scientists E. Haeckel and F. Müller conducted serious embryological and comparative anatomical studies, which 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 widespread plant and animal objects in the world, in which parts of the body have a common origin and a unified plan of structure, although they may differ greatly in appearance. What led to their appearance?
Causes of occurrence
Evolutionary processes occur in populations of living creatures and underlie microevolution. The emergence of new species is possible due to the accumulation in organisms of ever greater differences affecting both their structure and function. The process leading to the divergence of morphological and anatomical features that occurs as an organism's response to changing environmental factors is called divergence. Homologists are parts of the body of individuals that undergo natural selection and are formed as a result of adaptation to the conditions of their environment. They are studied in detail in the course of zoology. Let's consider them in more detail.
Features of the structure of vertebrates
The forelimbs of all mammals consist of the same bones: the humerus, ulnar, radial, bones of the wrist, metacarpus and phalanx of the fingers. But various environmental conditions over the course of evolution left their mark on both the shape of the skeleton of the forelimb and 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 organs such as homologues. This is confirmed by comparative anatomical studies not only among various groups of animals, but also in the plant world. We will consider them in the next paragraph.
Modifications of the autonomic organs
During ontogenesis, representatives of the flora world not only acquire new characteristics, but also modify parts of their body. In botany, this phenomenon is called a modification of the vegetative parts and is considered as an adaptation that arose during phylogenesis. You can observe it with representatives of the flowering plant department. For 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 unified plan and performs functions common to all types: fixing in the soil, support, absorption and conduction of water and solutions of mineral substances. However, the appearance of the roots can vary greatly if they begin to perform special functions. So, the stilted roots of a pandanus growing in tropical swamps are homologous.
They do not allow the bottom of the stem to completely immerse in water, protecting it from decay. Orchids have aerial roots homologous to the underground organ - they are involved in extracting additional volumes of air for plant respiration. They serve as a reservoir accumulating starch and other organic compounds, beet and carrot root crops, Jerusalem artichoke and dahlia root tubers. All of the above modifications are homologs. This biology claims with good reason, since they correspond to each other and to the general principle of the structure of the underground organ - the root.
Homology in the human body
Representatives of the vertebrate class, which includes Homo sapiens, have a single plan for the structure of 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 animals, the phalanx of the thumb is opposed to the other four fingers, which is the result of the ability to work. Homologists are all these examples that have arisen in the process of anthropogenesis.