XH INTRODUCTION 



knowledge of the present state of learning in these several 

 branches of knowledge and to give him some idea of the 

 bearing of the various specialties upon man and the possibih- 

 ties of his further development. This book is one answer to 

 the lament of H. G. Wells when he says "If only the 

 scientists would tell us less mumblingly what it is all about!" 



We hve in a particular world. Our life and activities are 

 hedged in and controlled by the nature of the earth and the 

 universe of which it is a part. We have throughout the ages 

 speculated about the form and composition of our world and 

 have looked wonderingly at other spheres which seem to 

 our unaided eyes but tiny specks saihng through the firmament 

 of space. Great telescopes have been invented to enlarge the 

 reach of our weak eyes. Through these we explore the 

 heavens and in other ways we are getting shght tentative 

 knowledge of our neighbor worlds. The story of these 

 explorations into the far reaches of the universe is told in 

 Part I, with special attention to conditions of possible Hfe, 

 somewhat similar to ours, upon the other spheres. The mag- 

 nitude of space and the far stretch of time give perspective 

 to any consideration of man and his world today and in the 

 future. 



The stream of hfe upon our planet leading up to the races 

 of man, or the subdivisions of the human race, is discussed in 

 Part II. By such a critical examination of how changes and 

 new departures in organic hfe have come about we can look 

 to the future with at least scraps of knowledge of nature's 

 precedents. 



In addition to glimpses of the past, for the whole record 

 doubtless will never be unfolded, we need an understanding 

 of the materials nature has to work with in man: the structure 

 of the human body and the ways in which it performs its 

 functions. This subject is presented in Part in. 



As biological units we depend upon the world we live in 

 for food, for air and water and light and warmth. We are on a 

 planet teeming with multitudinous life in the form of 

 animals both large and microscopic and of almost infinite 

 varieties of plants, as well as of hundreds of millions of 

 other human beings. We must snatch the means of living 

 from this world; we are constantly influenced by heat and 



