Basics of Evolution - Korzh O.P. - 2006

Part II. MACROEVOLUTION

Chapter 11. Means of Transformation of Organs and Functions

11.1. Prerequisites for the Evolution of Organs and Functions

Since Organs and the Functions they perform are closely interrelated, their evolution proceeds in parallel. It is incorrect to ask which changes first—the organ or the function—since this happens simultaneously. One of the universally recognized properties of organs is their multifunctionality. New, and sometimes even unexpected, functions are revealed later through deeper studies of organisms. Naturally, various organs differ to a certain extent in their functional capabilities, which is most clearly observed in receptors that are specific to certain stimuli.

It turns out that sometimes even highly specialized organs perform a whole range of functions. Thus, any plant organ, In addition to its primary functions, can perform others: a leaf, besides Photosynthesis and Transpiration, is sometimes used as a storage organ for nutrients and Water, for Vegetative Reproduction, The excretion of waste products, and so on. This can even apply to Tissues: Vascular Tissues in plants also perform a supporting function, while the epidermis with Stomata, in addition to protection against desiccation and the Adverse effects of sunlight or wind, helps regulate moisture evaporation (transpiration) and gas exchange.

Multifunctionality is also characteristic of animal organs, but the human hand must be recognized as the most universal organ, possessing an extraordinary number of functions. Internal Organs are similarly multifunctional—even vestigial organs play a certain role in the functioning of the Organism (the Appendix, having lost its digestive function, remains one of the organs responsible for the body's immune responses).

This is explained by the fact that unicellular organisms initially performed all vital functions. Similarly, prior to differentiation, all Cells are totipotent, meaning they can theoretically perform almost all functions. Perhaps the suppression of some functions and the dominance of others is a consequence of differentiation, modulated to a certain extent by the organism.

One of the prerequisites for the evolution of organs and functions is quantitative Changes in the latter, that is, the intensity of their manifestation. This applies both to different species that differ from each other in most functional characteristics, and to individual organisms of the same species, since the heterogeneity of the latter is also evident at the functional level. For example, the speed of locomotion varies not only among different species (hare, wolf, horse, etc.), but also among different individuals of these species, which is determined by their individual characteristics.

Quantitative changes in functions can be caused by Variability in the number or size of homogeneous structures that perform them. It should be borne in mind that any functions of an organism change quantitatively and even qualitatively during ontogeny. A clear example of qualitative changes in functions is metamorphosis, especially when the larval and adult forms develop in different environments.

Thus, the multifunctionality of organs and the possibility of quantitative changes in functions serve as the main prerequisites for the evolutionary transformations of organs during phylogeny.

Features and properties of organisms that share a common origin despite having different Anatomical and morphological structures are called homologous, whereas organs that share an external similarity but have an independent origin are called analogous (Fig. 11.1). Analogy is always caused by similarities in lifestyle (wings in flying animals—birds, insects, reptiles, etc.; the digging limb of the mole cricket and the mole, among other Examples). Homology is based on similarities in genotypes and the initial Stages of Ontogeny, while differences in the Structure and functioning of these organs are caused by the divergence of organisms into different ecological niches (the limb of a horse, whale, bat, etc., is the result of these animals' adaptation to different living conditions).

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Fig. 11.1. Examples of ANALOGOUS AND HOMOLOGOUS organs in plants and animals (according to various authors):

A - homology of fruit tissues in seed plants: 1 - orange; 2 - tomato; 3 - Ovary absent; 4 - strawberry; 5 - apple; B - limb homologues in Arthropods: 1 — crayfish claw; 2 — copulatory organ; 3 — swimming leg of a water beetle; 4 - walking leg of an insect; 5 - antenna; 6 - Mandible; C - analogous ROOT-like structures in plants: 1 - mallow roots; 2 - moss rhizoids; 3 - root-like submerged leaf of Salvinia; D - wing analogues in animals: 1 - butterfly; 2 - bird; 3 - bat