ATMOSPHERIC FACTOR IN EVOLUTION. 297 



We are speaking- of Atmospheric variation as a factor in 

 organic evolution, but nowadays there is also an inorganic 

 evolution talked of. By inorganic evolution is meant, in the 

 M-ords of Professor Duncan, that 



"The 80 odd elements of matter as we know them on the earth to-day 

 were not specially created, but like the plants and animals they have truly 

 evolved from simpler and still simpler types back to some really simple 

 elements from which they have all evolved through infinite aeons gone by. ' * 



The simplest forms of matter appear in the hottest stars, 

 where the elements of lightest atomic weight first appear; then 

 as the temperature gets less, more complex elements appear, 

 until ultimately, at the ordinary temperature of to-day we have 

 the varied and complex matter of to-day. We see then that 

 the governing factor in inorganic evolution is change of tem- 

 perature. Now let us turn to organic evolution. Here the 

 change is from the lowest form of plant life to the highest form 

 of animal, as exemplified in man or homo sapiens. In bringing 

 this great change about, I hold that the most potent factor was 

 the accompanying change which was going on gradually and 

 steadily in the atmosphere, namely the gradual elimination of 

 carbon from it. Just as a change of temperature was the 

 dominant factor in inorgaic evolution so was change of air, that 

 is, change of food, the dominant factor in organic evolution. 

 This, too, is just what we should expect. For as temperature 

 is the most important condition to an inorganic substance, so is 

 jood the most important to an organic. The quickest way of 

 producing a change in an inorganic substance is to change its 

 temperature, so, with a living organism, if you want to change 

 it, change its food. I am told that it is now possible to rear 

 as many queen bees as you wish in one hive, simply by feeding 

 as many ordinary bees as are required on the special food 

 usually reserved for the queen bee ; and by giving tjhem, of 

 course, the necessary room for expansion. It is also by change 

 of food under cultivation and domestication that we have got 

 such a rapid improvement of late years in so many of our 

 flowers and domestic animals. 



Now, since the dawn of organic life, the food of all things 

 living has ben gradually changing ; for the air in which they 

 live and move, and from which they hav\2 their being has been 

 changing ; the carbon dioxide for the plants has been getting less 

 and less, while the oxygen for the animals has been getting more 

 and more. It may be urged that, at the beginning the con- 

 ditions were favourable to plant life, but unfavourable to animal 

 life; and that thus there is a diflficulty in explaining the origin 

 of animal Ufe. There is an appearance of truth here, but that 

 is due to our thinking of animals as we know them to-day, and 

 forgetting that the first animals would be such as could live in 

 a minimum of oxygen. 



Let me here recall the proposition with which I started, 

 namely, that not only is the animal life dependent on the plant 

 life, but conversely plant Ufe is ultimately dependent on the 



" R, K. Duncan: " The New Knowledge " p. 206. 



