EVOLUTIONARY ASPECTS IN MAMMALS 



Next, I have a few closing words about the role of behavior. 

 The almost unbelievable achievement in the temperature regula- 

 tion of reptiles, reached solely by behavioral means, ought to be 

 a strong reminder to all of us that we can also reasonably expect 

 behavior to play a crucial role in temperature regulation in mam- 

 mals. This I am sure we all agree upon, but in our laboratory 

 experiments we necessarily have to dispense with most of the sub- 

 jects' opportunities for behavioral regulation. Our knowledge 

 regarding the role of behavior in the physiological phylogeny of 

 temperature regulation is therefore very limited. In the monotremes 

 it is of paramount importance. In the primitive Echidna behavior 

 seems to be the only way heat dissipation can be effected and is 

 thus of vital consequence, particularly on the hot side. To evaluate 

 the importance of behavior along the phylum is virtually impos- 

 sible, and I will make no attempt to do so. With the increasing 

 development of the cerebral capacity, behavior may reach ultimate 

 sophistication in man with his air-conditioned houses. Physiolo- 

 gists and anthropologists have thus taught us that man's invasion 

 of the climatic extremes, such as the Eskimos, Lapps, and others, 

 is almost entirely achieved by behavior, with rather subtle changes 

 in physiological adaptation. Since we are discussing evolution, it 

 may be of interest thatbehavior may also show regression as a fac- 

 tor in human temperature regulation. I am referring to man's or 

 more correctly, woman's vanity, explicit in sheer nylon stockings 

 in 40 G below weather, readily observable in the streets of 

 Fairbanks every winter. 



An important part of the armadillo's temperature regulating 

 ability is represented by its behavioral pattern. Thus, there is no 

 doubt that the ball- like posture is an extremely important means 

 of increasing the insulation. Measurements made by Buttner (1938) 

 demonstrate a reduction of 50% in the surface area when a man 

 curls into ball- like posture. The importance of posture was shown 

 clearly for the armadillo as well by the skin temperature measure- 

 ments and the experiments with the heat- flow discs. The building 

 of nests is also a most important factor in survival during exposure. 

 Without overstating it, nest- building seems to be a highly developed 

 social habit which is of the greatest functional significance in the 

 survival and expansion of the species. It is of particular interest in 



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