No isolated experiment, however significant in itself, can suffice for the experimental demonstration of any natural phenomenon; for the "one chance in a million" will undoubtedly occur, with no less and no more than its appropriate frequency, however surprised we may be that it should occur to us.

The best causes tend to attract to their support the worst arguments, which seems to be equally true in the intellectual and in the moral sense.

The neutral zone of selective advantage in the neighbourhood of zero is thus so narrow that changes in the environment, and in the genetic constitution of species, must cause this zone to be crossed and perhaps recrossed relatively rapidly in the course of evolutionary change, so that many possible gene substitutions may have a fluctuating history of advance and regression before the final balance of selective advantage is determined.

We can set no limit to human potentialities; all that is best in man can be bettered; it is not a question of producing a highly efficient machine, ... but of quickening all the distinctly human features, all that is best in man, all the different qualities, some obvious, some infinitely subtle, which we recognize as humanly excellent.

Natural selection is a mechanism for generating an exceedingly high degree of improbability.

Inductive inference is the only process known to us by which essentially new knowledge comes into the world.

We may consequently state the fundamental theorem of Natural Selection in the form: The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time.