Difficulties on the theory of descent with modification -- Transitions -- Absence or rarity of transitional varieties -- Transitions in habits of life -- Diversified habits in the same species -- Species with habits widely different from those of their allies -- Organs of extreme perfection -- Means of transition -- Cases of difficulty -- Natura non facit saltum
-- Organs of small importance -- Organs not in all cases absolutely perfect -- The law of Unity of Type and of the Conditions of Existence embraced by the theory of Natural Selection.
Abstract: The adage Natura non facit saltum was, as is well known, adopted by Alfred Marshall as the motto for his Principles of Economics, most probably as a borrowing from Charles Darwin's Origin of Species.
It [the First edition of the Principles] also contained a motto, Natura non facit saltum, adopted perhaps from Kant, perhaps from Darwin's Origin of Species.
Those manifestations of nature which occur most frequently, and are so orderly that they can be closely watched and narrowly studied, are the basis of economic as of most other scientific work; while those which are spasmodic, infrequent, and difficult of observation, are commonly reserved for special examination at a later stage: and the motto Natura non facit saltum is specially appropriate to a volume on Economic Foundations (Preface, p.
Thus progress itself increases the urgency of the warning that in the economic world, Natura non facit saltum (ibid.
Natura non facit saltum (Frontispiece, from first edition).