Human Anatomy (with Fundamentals of Dynamic and Sports Morphology) - Ivanitsky, M. F. 2008

Age Morphology
Developmental Acceleration and Factors of Ontogenesis

Developmental acceleration is an acceleration of human Organism GROWTH AND DEVELOPMENT processes characteristic of the modern historical epoch,

leading to an increase in definitive body size compared to individuals of preceding generations in the same age groups. This developmental acceleration shortens the duration of the evolutionary stage of human ontogeny (see p. 421). Morphological acceleration is combined with the accelerated "maturation" of body Functions (including motor function) and manifests both during the prenatal period (affecting the body size of newborns) and after birth, particularly clearly in adolescence. Its other manifestations include the accelerated maturation of the Skeletal System (Changes in the timing of ossification), earlier tooth eruption, and larger body sizes in comparable age groups compared to children of the early and mid-20th century.

From generation to generation, the age of menarche shifts to progressively earlier periods. A striking comparison can be seen in the age of menarche among Polish women of three related generations: grandmothers, mothers, and daughters. In 1911, the average age of menarche for the grandmothers was 14.5 years, for the mothers in 1935 it was 13.9 years, and for the daughters in 1959 it was 12.1 years.

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Fig. 148. Monozygotic twins (boys), 8 years old. Along with facial resemblance, they show an identical pattern of Ossification of the hand Skeleton.

Disharmonious acceleration of development is frequently observed, where the maturation of certain Organs significantly outpaces others. For instance, against the backdrop of accelerated linear body growth, The Development of The Heart Muscle may be delayed, impairing the supply of oxygen and nutrients to the body. Consequently, children's physical endurance is reduced, and the development of several motor skills also fails to reach the proper level. Children with disharmonious developmental acceleration require special attention from physicians and educators.

Fig. 149. Dizygotic twins (girls), 5 years old. The degree of facial resemblance is lesser than in Fig. 148.

Significant intra-pair differences in the ossification of the hand skeleton

Along with accelerated development, a delay in age-related and senile bodily changes is also observed. This is manifested in the later cessation of menstruation in women (on average up to 50–51 years of age), thereby extending the reproductive period.

Secular acceleration of development is widespread everywhere—wherever the modern lifestyle has replaced centuries-old traditions. In this sense, it is a direct consequence of urbanization and industrialization. In major industrial centers, children's growth and development rates have now stabilized at a fairly high level. In small towns and rural areas, acceleration processes are still quite active.

Developmental acceleration is driven by the entire complex of modern living conditions shaped by civilization: dietary patterns rich in animal Proteins, The Use of pharmacological agents, informational stress (an Abundance of stimuli affecting the Central Nervous system), and the intermingling of previously isolated populations (due to religious and class barriers) leading to intergroup marriages. The latter factor promotes heterosis, which enhances growth activity and the vitality of the younger generation.

Factors of growth and Development of the organism. Growth and development result from a complex interaction between hereditary and acquired factors as the genetic program unfolds in a specific environment. The environment determines the extent to which this program is fulfilled. METABOLISM/18.html">The Influence of hereditary and environmental factors on growth and development is confirmed by the twin method of research, which has two main approaches. The first approach is based on comparing the degree of intra-pair variation between monozygotic (MZ)—genetically identical—and dizygotic (DZ)—genetically similar—twins (Fig. 148, 149), assuming that environmental conditions are identical for both partners in an MZ or DZ pair. Consequently, traits in which MZ twins exhibit greater intra-pair similarity than DZ twins are considered to be highly dependent on genetic influences.

The second approach of the twin method involves exposing twins (preferably MZ) to different environmental conditions (such as distinct upbringing regimes or educational curricula). Testing the separated twins (within a pair) before and after the experiment helps evaluate its effectiveness and outcomes.

Applying the first approach of the twin method has revealed several patterns. It has been established that body length is more strictly determined by heredity than body weight, and bone dimensions are more heavily influenced by heredity than the thickness of the muscular and subcutaneous fat layers (Fig. 150).

Fig. 150. Indices of hereditary influence (Holzinger's formula) for various structures of the upper arm and forearm: the numbers represent The ratio of hereditary influences to their total sum; diagonal hatching indicates Muscles, solid fill indicates the subcutaneous fat layer (for example, the thickness of the muscle and subcutaneous fat layers on the forearm is determined by heredity to a greater extent than on the upper arm).

Comparing the holistic characteristic of the organism (body type) with its individual components (development of the skeleton, Muscular System, and fat distribution) has demonstrated a greater hereditary Determination of the whole compared to its parts.

The degree of genetic influence varies across different stages of growth and development. The hereditary determination of total body size increases from the newborn period to middle childhood, followed by a subsequent decline by the age of 12–15 years. The absolute magnitude of morphological traits is more strongly conditioned by heredity than the rates of their change over time.