Essay On Endotherms

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Endotherms are described as organisms that are able to maintain a stable internal temperature, irrespective of the outside influence. This ability to control inner temperature is considered an important biological advancement in the evolutionary development because it allowed animal life to develop in environments with temperatures significantly different from those of the body. (9) It is the major feature of mammal and bird life that distinguishes them from reptiles and other vertebrates. Endothermy provides distinct psychological and ecological advantages, which allows for successful survival of mammals in wide range of aerial, aquatic and terrestrial environments. It allows them to maintain level of activity, which is beyond the capacity of endotherms. (6)
Mammals maintain a constant body temperature mostly by two ways. First, minimizing thermal conductance with fur, or storing large amounts of subcutaneous fat; Second, by maintaining a metabolic heat production which is equivalent to the rate at which body is losing heat to the environment. They tend to increase the amount of oxygen consumption significantly in cold temperatures to compensate for accelerated heat loss. Mammals also shiver in response to exposure to cold environments. However, there are placental mammals as well who rely on non-shivering thermogenesis for increased rate of metabolic heat production during long-term cold exposure. Brown adipose tissue is a specialized thermogenic tissue associated with hibernating and cold adapted mammals. (4)
It has been observed that the mechanisms used by homeothermic species to produce heat and maintain body temperatures are not new. They antecede homeothermy, which is supported by presence of similar mechanisms in lowe...

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...ansition. (7)
It is possible that one or multiple of the theories providing explanations to the evolution of complex characteristic of endothermy could be correct, however there is not enough fossil record to recover small changes associated with the evolution of fully expressed mammalian homeothermy. The correlated progression hypothesis supports that evidence from living amniotes or from fossils cannot be enough to reveal the sequence of mammalian endothermy because the ectotherms show few relevant signs of early endothermy, and mammals evolved from ancestors who had fully evolved endothermic mechanisms. There are several individual structures, processes and definable functions of endothermy, which evolved in a correlated progression. Endothermy cannot be separated as a single function from its integration with rest of the biological features of an organism. (7)

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