AND ITS INHABITANTS 175 



can be said. They probably became a part of man's cultural 

 inheritance so early that he still lived in his primeval home, 

 and had perhaps not begun to differentiate into races. If that 

 is the case, the climate was presumably of the kind which we 

 have found to be most stimulating. That is, it had a tempera- 

 ture about like that of modern Greece, but with much more 

 variability from day to day. As to fire, the conditions of its 

 discovery were probably like those of the first use of tools 

 and of speech. In this case, however, we can go farther. 

 Undoubtedly after man discovered that he could produce fire 

 artificially he first employed it primarily as a source of heat. 

 Only in a climate which had a distinct cold season would the 

 incentive to its use be great. Only in a climate where there 

 was plenty of wood and also a dry season to prepare the wood 

 for fuel would he find it easy to use the new discovery. More- 

 over, only in a relatively stimulating climate would early men 

 probably have had the energy to develop the highly laborious 

 art of firemaking, for few things require greater determination 

 and persistence. When some happy accident taught man the 

 value of heat in cooking food, the discovery doubtless spread 

 to warm regions, but it seems no great stretch of the truth to 

 infer that tropical man, if left to himself, would never have 

 become a user of fire. 



Discovery of use of iron. One of the next great steps in 

 human progress was the discovery of the use of iron. This 

 discovery required the concurrence of four important con- 

 ditions, all of which are much less likely to occur within the 

 tropics than without. First, there must be bits of ore lying 

 about where fires are likely to be made. Of course this may 

 occur in any part of the world, but it is far less likely to happen 

 within the tropics than farther north because the tropical soil 

 is generally so deep that rocks are rare. In the next place the 

 fires must be hot enough and of long enough duration to melt 

 the ore. This, too, may occur within the tropics, but is much 



