Terms of endearment.

In the animal psychobiology literature, the terms congenital, predetermined, heritable, and chronotypy each have meanings that can help differentiate implicit, sometimes hidden, elements of the broad and onerous term, "innate." Relevant phenomena in animals' nonverbal recognition and communication systems are discussed. Several ontogenetic analyses reveal that thermotactile stimulation and other forms of heat are potent determinants of learning and attachment in a variety of endothermic species. We describe preliminary data from language evolution and word usage that mirror physiological and affective aspects of thermal stimuli in development. Specifically, we examine the thermal and affective meaning of "warm" and "cool" in languages used in temperate and in tropical climates, as well as the histories of such words in languages that derived from remote linguistic origins, namely Indo-European and Proto-Uralic roots. In each of these languages, there have evolved conjoint thermal and affective meanings that suggest a reflection of fundamental homeothermic biology in the psychology of human language.