Heredity proposes and development disposes.

It is ... a sign of the times-though our brothers of physics and chemistry may smile to hear me say so-that biology is now a science in which theories can be devised: theories which lead to predictions and predictions which sometimes turn out to be correct. These facts confirm me in a belief I hold most passionately-that biology is the heir of all the sciences.

To deride the hope of progress is the ultimate fatuity, the last word in poverty of spirit and meanness of mind.

Science is the art of the solvable.

The intensity of a conviction that a hypothesis is true has no bearing on whether it is true or false. The importance of the strength of our conviction is only to provide a proportionately strong incentive to find out if the hypothesis will stand up to critical evaluation.

In all sensation we pick and choose, interpret, seek and impose order, and devise and test hypotheses about what we witness. Sense data are taken, not merely given: we learn to perceive.... The teacher has forgotten, and the student himself will soon forget, that what he sees conveys no information until he knows beforehand the kind of thing he is expected to see.

I shall borrow two words used for a slightly different purpose by the great demographer Alfred Lotka to distinguish between the two systems of heredity enjoyed by man: endosomatic or internal heredity for the ordinary or genetical heredity we have in common with animals; and exosomatic or external heredity for the non-genetic heredity that is peculiarly our own - the heredity that is mediated through tradition, by which I mean the transfer of information through non-genetic channels from one generation to the next.