" The theorem of Organic Evolution is one thing; the problem of 

 deciphering the lines of evolution, the order of phylogeny, the 

 degrees of relationship and consanguinity, is quite another. Among 

 the higher organisms we arrive at conclusions regarding these things 

 by weighing much circumstantial evidence, by dealing with the 

 resultant of many variations, and by considering the probability 

 or improbability of many coincidences of cause and effect; but 

 even then our conclusions are at best uncertain, our judgments 

 are continually open to revision and subject to appeal, ..." 



D'Arcy Wentworth Thompson, Growth and Form, igJJ. 



