Intensification of Function

one of the major pathways of the progressive transformation of organs in the course of animal evolution. Intensification of function is associated with the growing complexity of organ structure and leads to a general rise in the level of life activity.

An example of intensification of function is the complexity of structure and function of the lungs in terrestrial vertebrates. In amphibians the lungs have the appearance of thin-walled pouches, covered with a network of blood vessels. In reptiles, septa develop within the lungs, increasing the surface of epithelium that lines the interior of the pulmonary sacs. In the lungs of birds, the bronchial system is separated from the lung sacs. In mammals the lungs acquire a honeycomb structure and the diaphragm is formed in the thoracic cavity. As a result of intensification of function, the blood of the majority of mammals and birds contains 12–18 g of hemoglobin per 100 ml of blood, and that of amphibians and reptiles contains 6–10 g per 100 ml of blood.