An Early Passage on Taxonomy

NATURE, by descending gradually from great to small, from strong to weak, coun|terbalances every part of her works. Attentive solely to the preservation of each species, she creates a profusion of individuals, and supports by numbers the small and the feeble, whom she hath left unprovided with arms or with courage. She has not only put those inferior animals in a condition to perpetuate and to resist by their own numbers, but she seems, at the same time, to have afforded a supply to each by m...

 A Great Summary of Taxonmy

Branches or types are characterized by the plan of their structure,Classes, by the manner in which that plan is executed, as far as ways and means are concerned,Orders, by the degrees of complication of that structure,Families, by their form, as far as determined by structure,Genera, by the details of the execution in special parts, andSpecies, by the relations of individuals to one another and to the world in which they live, as well as by the proportions of their parts, their ornamentation,...

 Missing Links Make Defining Species Possible

As we trace the ancestry of modern Homo sapiens backwards, there must come a time when the difference from living people is sufficiently great to deserve a different specific name, say Homo ergaster. Yet, every step of the way, individuals were presumably sufficiently similar to their parents and their children to be placed in the same species. Now we go back further, tracing the ancestry of Homo ergaster, and there must come a time when we reach individuals who are sufficiently different fro...