PROGRESSION AND RETROGRESSION. 



191 



over, an insect at rest is not conditioned as an insect in the air. Let 

 it forsake little by little its aerial life, and rest longer and longer on 

 other bodies. In time it becomes a parasite. The structnre it had 

 acquired while in the air becomes useless. The environment being- 

 more stable, the opposing actions within are reduced, and the organ- 

 ism lapses into a simpler form. In the insect world we should find 

 the largest number of retrograded species, and so we do. Fleas, 

 bugs, the dream of which sends a shudder through our sleep, creep- 

 ers in the hair, burrowers in the flesh, form a descending, series, each 

 order carrying with it, in the form of vestiges, reminiscences of a 

 higher state when, as winged insects, its ancestors lived in the 

 open air. 



Retrogression of this kind has aflected higher orders. An am- 

 phibious mammal, taking less to the land and more to the water, 

 would lapse in time into a simpler form. The studies of Prof. Wilder 

 on the embryotic dugong seem to show that dugongs and manatees 

 have descended by retrogression from some ancient hippopotamoid 

 mammal. 



Retrogression, whose rationale is not found in our studies on the 

 Eolids, has affected still higher orders. If the elephants of our day 

 are descendants of the mastodons and mammoths which, in Pleisto- 

 cene days, possessed North America and Europe, as the investiga- 

 tions of Gaudry wellnigh demonstrate ; if the living tigers and lions 

 have descended from species whose remains abound in ancient caves, 

 as is probable; if the "grizzly" of the Rocky Mountains is a modified 

 form of the great cave-bear, once so common in Europe, as naturalists 

 believe ; if the anthropoid apes of Africa and tropical Asia are sur- 

 vivals from a race which spread beyond the tropics and ranked some- 

 what nearer to man, as the Mesopithecus of Greece and Dryopithecus 

 of France testify out of Miocene strata, the proboscidians, carnivores, 

 and primates have all sufiered retrogression, and, at the advent of 

 man, life having reached its zenith, animal life began a downward 

 curve. If, in the main, the higher has followed the loAver, within 

 this cycle of progression the struggle for life would involve another 

 cycle of retrogression. As the savage in pi'esence of civilization 

 often sinks to lower savagery, so a species, outstripped in the race of 

 life, and left hopelessly behind, degenerates, and finally dies. 



And as the two cycles, progression and retrogression, are involved 

 in the life-history of the earth, so the two movements may go on simul- 

 taneously in the same species. Man himself is such a species. His 

 brain, and its servant, the hand, have attained the utmost develop- 

 ment. His digestive system and his foot have been modified but 

 little from a primitive type. Progression above in that Avhich is most 

 distinctively human may involve retrogression below in that which is 

 distinctively animal. 



