THE 



AMERICAN JOURNALOFSCIENCE 



[FOURTH SERIES.] 



Aet. XL. — Polar Climate in Tim.e the Major Factor in 

 the Evolution of Plants and Animals ; by G. R. Wieland. 



The long period of physical evolution which preceded and 

 made possible the appearance of life on the globe forms a sub- 

 ject with which the physicist, the chemist, and the astronomer 

 must deal in common. For the history of these changes is an 

 inferential one based on the iDhysical properties, constitution, 

 and relative position of the materials of the globe in space. 

 And indeed the same is largely true of the immense period of 

 time which doubtless elapsed from the appearance of whatever 

 was the most primitive form of protoplasm to the evolution of 

 the oldest organisms now found fossilized. From this crucial 

 period onward, the paleontologist can decipher the main facts 

 in the story of life on the globe, although he can at no point 

 dispense with the mathematical sciences. Especially is this 

 true when it is attempted to gain a knowledge of climate in 

 time, certainly the most tangible and readily understood, and 

 doubtless the fundamental factor in evolution. To make this 

 latter statement clear let the extent to which organic growth 

 and life-processes involve chemism, be recalled in the light of 

 the more recent experiments of such investigators as Loeb and 

 Matthews, l^ow chemism refers solely to those properties of 

 matter which are unchangeable and eternal. On the other 

 hand, chemical change is governed by the conditions of elec- 

 trification, and of heat, light, and moistiire, which are none 

 other than the elements of climate, or weather conditions. Life 

 then, as far as we have succeeded in scrutinizing it, is a func- 

 tion of variable mechanical factors combined with chemism, 

 which is fixed, and of climate as dependent mainly on the 



Am. Jour. Sci. — Fourth Series, Vol. XYI, No. 96. — December, 1903. 



