On the Origin of Homeothermic Animals

Temperature has a fundamental influence in all chemical and biochemical reactions and physiological processes. Maintaining the relative constancy of the internal temperature (temperature homeostasis) is a necessary condition for normal life. Mammals and birds as well as humans have been found to be able to maintain a temperature homeostasis in the body (homeothermic animals). However, it is unknown the origin of homeothermic animals. It is assumed that homeothermy is not the result of the evolution of the central organ-based physiological mechanisms of thermoregulation. Homeothermy is the result of the evolution of some part of non-coding DNAs in the genome of the higher eukaryotes that led to the emergence of chromosomal heterochromatin regions (HRs). Chromosomal HRs are capable to form the condensed chromatin around the nucleus, which underlie the material basis of cell thermoregulation and responsible for dissipating excess heat energy from the nucleus into the cytoplasm. Homeotherms are animals in whose cells chromosomal HRs are able to form the densest layer of condensed chromatin with high thermal conductivity capable efficiently removing excess heat from the nucleus to ensure the implementation of a very high level of cellular metabolism.