The anatomy and physiology of temperature regulation was reviewed. The review supports the view that the temperature-regulating systems in animal life are inherently and irreducibly complex. Life can survive only if a relatively narrow temperature window is maintained. For humans, only 7° above normal can be lethal. For some birds and mammals the allowable range is greater, but still within certain limits. Several attempts to explain this complexity by evolution were also reviewed, concluding that evolutionists have not even been able to postulate “just-so” stories to explain their evolutionary theories. They admit that, although temperature regulation is an important consideration in evolution, no progress has been made towards viable explanations of the evolution of these systems in the past century.