Each individual has a certain duration of existence, during which a series of successive quantitative and qualitative changes occur, manifested in the form of growth and development. The growth and development of an organism are complex phenomena, the result of many metabolic processes and cell reproduction, an increase in their size, processes of differentiation, shaping, etc. It is during the growth and development of the organism that the unique hereditary program (genotype) is realized into its external manifestation (phenotype) under the influence and control of various and always unique environmental factors.
The individual development of an individual from the moment of birth to the natural completion of the life cycle is called ontogeny.
The “appearance” of all types of variability of human biological characteristics is associated with the transformations that occur in the process of ontogenesis.
Knowledge of the patterns, causes and factors of this process serves as a scientific basis for finding means of influencing human development, which is of paramount importance for medical practice.
The study of ontogenesis provides a unique key to understanding the phenomenon of human biological variability. This knowledge is essential for understanding individual differences in the form and functions of the body, since many of these features are determined by differences in the relative growth rate of individual parts of the body. The study of the developmental process is important for elucidating the mechanisms of human evolution, since the evolution of morphological traits in many respects comes down precisely to a change in genetically determined growth and development.
Different sides (aspects) of this phenomenon are studied by embryology and developmental biology, physiology and biochemistry, molecular biology and genetics, medicine, pediatrics, developmental psychology and many other disciplines. A separate area of biological anthropology is devoted to the same problem – age anthropology or auxology (from the Greek auxano – to grow).
The purpose of the work is to familiarize with the characteristics of the stages of ontogenetic development.
1. Define the concepts and essence of ontogeny
2. Study the main stages of ontogeny
3. Determine the integrity and sustainability of ontogeny
THE CONCEPT AND ESSENCE OF ONTOGENESIS
Ontogeny is the individual development of an organism, a set of successive morphological, physiological and biochemical transformations that an organism undergoes from the moment of its inception to the end of life. Ontogeny includes growth, i.e., an increase in body weight, size, differentiation.
Ontogeny, or the life cycle, is one of the key biological concepts. It was first used by E. Haeckel (1866) when formulating his biogenetic law, meaning by ontogeny only the process of intrauterine development. At present, this term is associated with the entire spectrum of successive transformations of the body from the moment of conception to the end of the life cycle (death).
Ontogeny (from the Greek ontos – being and genesis – origin) is life before and after birth, it is a continuous process of individual growth and development of the organism, its age-related changes.
The development of an organism should by no means be presented as a simple increase in size. Human biological development is a complex morphogenetic event. This is the result of numerous metabolic processes, cell division, an increase in their size, the process of differentiation, shaping of tissues, organs and their systems.
Ontogeny can be considered as a process of emergence and transformation of various features of an organism (features and systems of signs). Under the influence and control of various and always unique environmental factors (development modifiers), in the course of growth and development, a unique genetic material (genotype) is realized into its “external” manifestation (phenotype).
Human ontogenetic development can be characterized by a number of common features. These include:
Continuity – the growth of individual organs and systems of the human body is not endless, it goes according to the so-called limited type. The final values of each trait are genetically determined, that is, there is a reaction norm. But our body is an open biological system – it is the subject of constant continuous development throughout life. There is not a single parameter (and not only biological) that would not be in development or change throughout life.
Graduality and irreversibility – the continuous process of development can be divided into conditional stages – periods, or stages, of growth – going sequentially one after another. It is impossible to skip any of these stages, just as it is impossible to return exactly to those features of the structure that have already manifested themselves in the previous stages.
Cyclicity – although ontogeny is a continuous process, the rate of development (the rate of change in traits) can vary significantly over time. In humans, there are periods of activation and inhibition of growth. There is a cyclicality associated with the seasons of the year (for example, an increase in body length occurs mainly in the summer months, and weight – in the fall), as well as a daily cycle (for example, the greatest growth activity occurs at night, when the secretion of growth hormone (GH) is most active) and a number of others.
Heterochrony, or diversity of time (the basis of allometricity), as we have already noted, manifests itself in the unequal rate of maturation of different systems of the body and different signs within the same system. Naturally, the most important, vital systems mature at the first stages of ontogenesis.
Sensitivity to endogenous and exogenous factors – growth rates are limited or activated by a wide range of exogenous environmental factors. But their influence does not take the processes of development beyond the boundaries of the broad norm of reaction determined hereditarily. Within these limits, the developmental process is kept by endogenous regulatory mechanisms. In this regulation, a significant proportion refers to the actual genetic control, implemented at the level of the organism due to the interaction of the nervous and endocrine systems (neuroendocrine regulation). There is a regulation of a different nature, for example, biomechanical (mutual correlation of signs) or tissue (due to the interaction between tissues during growth).
Sexual dimorphism. Sexual dimorphism is the clearest characteristic of human development, and it manifests itself at all stages of its ontogeny (although with varying degrees of severity for different systems of traits). Let us remind once again that the differences caused by the “sex factor” are so significant that ignoring them in research practice negates the significance of even the most interesting and promising works. Naturally, data on the growth and development of men and women are compared with each other, but in no case are mixed in auxological studies.
Another fundamental characteristic summarized from all the above is the individuality of the process of ontogenesis. People are born, grow, develop, grow old, die in accordance with certain patterns, many of which are known to us for certain. But the dynamics of the ontogenetic development of an individual is unique. It is predictable only in general terms, from other – unique “details” – the morphological individuality of a person is formed. The individuality of development is one of the general characteristics of ontogeny. Despite the strange combination of words, this is the law.