206 UNIVERSITY OF MISSOURI BULLETIN 



history of the science, and, as the static view in the former 

 has given way to the genetic, in the field of animate nature 

 the beHef in the stability and permanence of specific forms, 

 sheltered and entrenched for, many centuries, has at last been 

 dislodged after repeated assaults, and the doctrine of the 

 common descent of living things has been finally established. 



Although abundant and adequate grounds existed before 

 Darwin's time for the complete rejection of the static view 

 of organic nature, so tenacious of life was the conception of 

 the immutability of species, that its deathblow was not given 

 until the publication of Darwin's "Origin of Species" in 1859, 

 and this date marks the beginning of the period in which the 

 evolutionary account of living things became generally ac- 

 cepted. 



The opposing conception, which regarded species as fixed, 

 permanent, objective realities, the result of a single act of 

 creation or the result of many special acts, was replaced, then, 

 by the doctrine of organic descent, which has now been shown 

 by an overwhelming mass of evidence to be the only tenable 

 view of the origin of diverse living forms, whatever may be 

 the causes of the evolutionary change itself. 



Evolutional science in biology is both an historical and an 

 experimental study, and we may draw a fairly sharp line of 

 demarcation between these two aspects presented by the prob- 

 lem of organic descent. Historically considered, it is an 

 attempt to reconstruct in the imagination the past course of 

 descent through which both extinct and extant forms of living 

 things have been evolved from simpler ancestral stages. The 

 method pursued is largely one of speculation and the evidence 

 at best circumstantial. While the conclusion is now beyond 

 all question that the countless diverse forms of life have arisen 

 through a gradual development, when we attempt to trace 

 the actual paths which the descent has followed or, in other 

 words, to rebuild the genealogical tree, we are met with in- 

 superable obstacles at every point, for so fragmentary are the 



