THE FAILURES OF ARBOREAL LIFE 213 



eating ants, or an adaptation for any other very definite 

 and special type of food, has proved the downfall of many 

 a promising animal type. The Primate and human stock 

 has not been led astray in this direction; for it has pre- 

 served throughout that well-balanced habit of dietary, 

 only to be termed omnivorous. To talk in the fashion 

 of human successes in life, an_ammal may use or abuse 

 its life surroundings. We may say that when it uses 

 them rightly it undergoes the successful minimal adaptive 

 specialization, but when it abuses them it runs riot in 

 specializations specializations which ultimately make it 

 the slave of its environment. 



An animal which chances to come into possession of 

 a habitat of which one feature is the presence of water 

 be it rivers, lakes, or oceans in which food is to be ob- 

 tained will open up a wider field for its activities, gain a 

 new series of educational possibilities, and perhaps place 

 itself beyond the competition of a rival by acquiring, in 

 some degree, an aquatic habit. To be at home both 

 upon the land and in the water offers a wider field under 

 normal circumstances, and a useful, possibly life-saving 

 alternative under abnormal circumstances, that is an 

 obvious asset to the animal. But to go much further 

 than this in the cultivation of an aquatic habit is to court 

 disaster, since a purely aquaticT life is one singularly 

 barren of educational possibilities. Limbs become re- 

 duced to paddles ; smell, hearing, and even sight, become 

 restricted senses, and an animal wholly dependent on a 

 thoroughly aquatic life is one debarred from real mam- 

 malian progress. The Sirenia, Cetacea (toothed and 

 toothless) and even the Pinnipeda among the Mammals, 

 are examples of types which, having become slaves of 

 an aquatic habit, and leading singularly restricted, 

 though highly specialized lives, have fallen behind in the 

 march of progress. It is notorious how long in geological 

 history these animals have been, as it were, finished 

 organisms. 



