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.
Most can I think be satisfactorily answered.--'Natura non facit saltum' answers some of the most obvious.--The slowness of the change, and only a very few undergoing change at any one time answers others.
Thus progress itself increases the urgency of the warning that in the economic world, Natura non facit saltum (ibid., p.
Natura non facit saltum (Frontispiece, from first edition).
The truth of this remark is indeed shown by that old canon in natural history of 'Natura non facit saltum.' 194 [VI: DIFFICULTIES ON THEORY]
 The canon of 'Natura non facit saltum' applies with almost equal force to instincts as to bodily organs.
Rosenstein-Rodan's 1984 article described the essence of his early thought about development as "natura facit saltum-nature does make a jump, the opposite of the motto natura non facit saltum that Alfred Marshall thought appropriate for economics" (p.
Rosenstein-Rodan believed that the theory of the big push contradicts the conclusions of the traditional static equilibrium theory (and reverses the famous motto natura non facit saltum) in three different ways.