132 COACTION: THE INTERRELATIONS OF ORGANISMS 



assumes that the human type separated from the rest of the anthro- 

 poid stock through (a) the adoption of life on the ground, (6) the 

 addition of flesh to a diet of fruit and green plants or the assumption 

 of a more or less complete flesh diet, and (c) hunting in packs. Such 

 hunting would be a necessity only when food from plant sources failed 

 in the dry or cold season. 



Recourse to the social hunting of large game in a climate with 

 severe winters is exemplified by the wolves. During the summer their 

 food consists of small mammals, birds, bird's eggs, and even insects, 

 but in winter this kind of food is inadequate or wanting and coopera- 

 tion becomes requisite to the securing of large mammals. Olson 

 (1938, a) has mapped wolf dens and hunting-pack routes in the Supe- 

 rior National Forest and Quctico Park. One main traveled trail to 

 the northeast forms a narrow ellipse about 60 miles long and 15 wide, 

 while the southwesterly course constitutes a similar ellipse approxi- 

 mately 90 miles in length. Each of these appears to be hunted over 

 at fairly regular intervals. Family dens are scattered about near the 

 hunting trail, and the size of the pack naturally varies with the num- 

 ber of families participating. Social organization also accompanies 

 hunting habits in other genera (Houssay, 1893), as well as in other 

 groups, such as certain steppe birds in Asia (Brehm, 1896), and South 

 American weasels and birds (Hudson, 1892). It has been noted in a 

 high degree of perfection in fishing squadrons of the white pelican on 

 lakes of Southern California (cf. Bailey, 1917:43). 



The Prey of Carnivores. The distinction between carnivorous 

 species and insectivorous or omnivorous species is far from absolute. 

 Most of the carnivores eat insects regularly or on occasion, even the 

 cougar being said to take grasshoppers, while mole and shrew feed 

 upon flesh to some degree. ]\Iore than half of the common carnivores 

 of North America eat fruits to some extent, with the consequence that 

 this group passes more or less gradually into the omnivores. Not- 

 withstanding these exceptions, the general habits of the group are 

 well marked and are reflected in dentition, claws, and other structural 

 features. 



Life habits characteristic of the herbivorous mammals are found 

 in somewhat less degree among the carnivores. The marten is arbor- 

 eal, and its relative, the fisher, rather less so. The foxes and M'olves 

 are cursorial; the weasels and skunks exhibit the ferreting life habit; 

 the hog-nosed skunk is more or less of a rooter, and the badger fos- 

 sorial. The natatorial habit is represented by the otter; the mink is 

 essentially amphibious, and the fisher rather less of a swimmer. 

 Nearly all the group exhibit a strong tendency to be nocturnal, and 



