A species is a reproductive community of populations reproductively isolated from others that occupies a specific niche in nature.

Wherever we look at the living biota … discontinuities are overwhelmingly frequent…The discontinuities are even more striking in the fossil record. New species usually appear in the fossil record suddenly, not connected with their ancestors by a series of intermediates.

I had found again and again that the most aberrant population of a species - often having reached species rank, and occasionally classified even as a separate genus - occurred at a peripheral location, indeed usually at the most isolated peripheral location.

It seems to me that for Darwin the pulsing of evolutionary rates was a strictly vertical phenomenon.

Biology can be divided into the study of proximate causes, the study of the physiological sciences (broadly conceived), and into the study of ultimate (evolutionary) causes, the subject of natural history.

A species consists of a group of populations which replace each other geographically or ecologically and of which the neighboring ones integrate or hybridise wherever they are in contact or which are potentially capable of doing so (with one or more of the populations) in those cases where contact is prevented by geographical or ecological barriers.

The most consequential change in man's view of the world, of living nature and of himself came with the introduction, over a period of some 100 years beginning only in the 18th century, of the idea of change itself, of change over periods of time: in a word, of evolution.