| Show TAILS ARE SHORTER IN COOL CLIMATES study of genetics produces interesting data new york races of mammals inhabiting cooler regions have relatively shorter tails legs and ears than races of the same species from warmer regions according to a study of genetics and the origin of species issued by the columbia university press among birds the same is true for the relative lengths of beak legs and wings races of mammals and birds and some invertebrates living in cooler climates are larger in body size than races of the same species in warmer climates in mountain countries races from higher elevations are larger than those from the lower ones races of mammals from warmer countries have shorter but relatively coarser hair and less down than races from cooler countries an exposure of a mammal to cold or heat may produce respectively an increase or a decrease of the hair length a change that is quite analogous to that distinguishing the geographical races from the high and low altitudes says the author of the study professor dobzhansky of california institute of technology in summarizing mar izing findings in this field how nature works butterflies resembling the varieties known from syria and southern italy have been obtained he points out from the pupae of the central european races of the same species exposed to heat treatment on the other hand treatment of the central european race with cold has resulted in a resemblance to the form from northern scandinavia di the adaptive value of the development of longer hair and a greater amount ot of wool in a cool climate is indeed obvious the fact that the races of mammals inhabiting cold countries usually have longer hair and more down than races of the same species from hot countries is consequently evidence evid enca for and not against the effectiveness of natural selection the rule of large body size in the cool and small size in the warm climates is concerned with the temperature pera ture regulation of the animal A large body size is correlated with a relatively smaller body surface and consequently with a more limited loss of heat the protruding body parts the extremities tails and ears are especially subject to a rapid loss of heat the increase of the body surface in just these regions is therefore unfavorable in the cold and may prove desirable in the warm climates in warm and cool regions in mammals and birds races inhabiting warm and humid regions have more dark brown or black pigmentation or coloring than races of the same species in cooler or drier regions the ari arid d desert regions are characterized by races with an accumulation of yellow and reddish brown pigmentation among insects the pigmentation increases under humid and cool condition and decreases in the dry and hot regions the humidity being apparently more effective than temperature for the ladybird beetles eastern asia northeastern siberia japan is the center of heavily pigmented races going southwest and southeast from there we encounter lighter and lighter races of the species until centers of very pale races are reached in southern california in the western and in turkestan Turk estan in the eastern hemisphere it is interesting that although the darkest and lightest races respectively ively are usually confined to the centers just defined the exact location of the center is somewhat variable for different species thus in some of the old world species the maximum is observed in russian turkestan Turk estan in others in chinese turkestan Turk estan and in suu still others in persia |
