Thoughts on Species. 377 



To understand these variations, we may again appeal to general 

 truths. 



Variation is a characteristic of all things finite ; and is involved 

 in the very conditions of existence. No substance or body can 

 be wholly independent of every or any other body in the uni- 

 verse. The most comprehensive and influential law in nature 

 most fundamental in all change, composition or decomposition, 

 growth, or decay, is the law of mutual sympathy, or tendency to 

 equilibrium in force through universal action and reaction. 



The planets have their orbits modified by other bodies in 

 space through their changing relations to those bodies. A sub- 

 stance, as oxygen or iron, varies in temperature and state of ex- 

 pansion from the presence of a body of different temperature ; 

 in chemical tendencies from the presence of a luminous body 

 like the sun ; in magnetic or electrical attraction from sur- 

 rounding magnetic, or electrical influences. There is thus un- 

 ceasing flow and unceasing change through the universe. All 

 the natural forces are closely related as if a common family or 

 group, and are in constant mutual interplay. 



The degree or kind of variation has its specific law for each 

 element ; and in this law the specific nature of the element is in 

 a degree expressed. There is to each body or species, the nor- 

 mal or fundamental force in which its very nature consists ; and 

 in addition, the relation of this force to other bodies, or kinds, 

 amounts or conditions offeree, upon which its variations depend. 

 One great end of inorganic science is to study out the law of 

 variables for each element or species. For this law is as much a 

 part of an idea of the species, as the fundamental potentiality ; 

 indeed the one is a measure of the other. 



So again, a species in the organic kingdoms is subject to varia- 

 tions, and upon the same principle. Its very development de- 

 pen,ds on the appropriation of material around it, and on attend- 

 ing physical forces or conditions, all of which are variable 

 through the whole of its history. Every chemical or molecular 

 law in the universe is concerned in the growth, — the laws of 

 heat, light, electricity, cohesion, 6tc. ; and the progress of the 

 developing germ, whatever its primal potentiality, is unavoid- 

 ably subject to variation, from the diversified influences to 

 which it may be exposed. The new germ, moreover, takes 

 peculiarities from the parent, or from the circumstances to which 

 its ancestry had been exposed during one or naore preceding 

 generations. 



