“Darwin believed that the crossing of two types generally led to a blend, and that consequently bisexual reproduction tended to make a species uniform. He therefore had to postulate some cause constantly at work to keep up the inheritable variation within a species. He very naturally looked to the effects of differences of environment. …It was shown that Darwin had been wrong in supposing that variations due to environment were inheritable. Selection merely picked out the best available line from a given population, and would not, as Darwin had believed, give rise to an unlimited amount of change.”

— J. B. S. Haldane, book The Causes of Evolution

Introduction, pp.14-20.
The Causes of Evolution (1932)

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J. B. S. Haldane32

Geneticist and evolutionary biologist 1892–1964

Related quotes

“As systematic inquiry into the natural facts was begun it was at once found that the accepted ideas of variation were unfounded. Variation was seen very frequently to be a definite and specific phenomenon, affecting different forms of life in different ways, but in all its diversity showing manifold and often obvious indications of regularity. This observation was not in its essence novel. Several examples of definite variation had been well known to Darwin and others, but many, especially Darwin himself in his later years, had nevertheless been disposed to depreciate the significance of such facts. They consequently then lapsed into general disparagement. Upon more careful inquiry the abundance of such phenomena proved to be far greater than was currently supposed, and a discussion of their nature brought into prominence a consideration of greater weight, namely that the differences by which these definite or discontinuous variations are constituted again and again approximate to and are comparable with the class of differences by which species are distinguished from each other.”

William Bateson (1861–1926) British geneticist and biologist

Preface
Problems In Genetics (1913)

“Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.”

Charles Darwin book On the Origin of Species (1859)

Source: On the Origin of Species (1859), chapter III: "Struggle For Existence", page 61 http://darwin-online.org.uk/content/frameset?pageseq=76&itemID=F373&viewtype=image <br class="br">Context: Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.

“Physiologic facts concerning the origin of species in nature were unknown in the time of Darwin... The experience of the breeders was quite inadequate to the use which Darwin made of it. It was neither scientific, nor critically accurate. Laws of variation were barely conjectured; the different types of variability were only imperfectly distinguished. The breeders' conception was fairly sufficient for practical purposes, but science needed a clear understanding of the factors in the general process of variation. Repeatedly Darwin tried to formulate these causes, but the evidence available did not meet his requirements.
Quetelet's law of variation had not yet been published. Mendel's claim of hereditary units for the explanation of certain laws of hybrids discovered by him, was not yet made. The clear distinction between spontaneous and sudden changes, as compared with the ever-present fluctuating variations, is only of late coming into recognition by agriculturists. Innumerable minor points which go to elucidate the breeders' experience, and with which we are now quite familiar, were unknown in Darwin's time. No wonder that he made mistakes, and laid stress on modes of descent, which have since been proved to be of minor importance or even of doubtful validity.”

Hugo De Vries (1848–1935) Dutch botanist

Species and Varieties: Their Origin by Mutation (1904), The Open Court Publishing Company, Chicago, p. 5-6

“Evolution in… cases has clearly been a very slow and almost (if not quite) continuous process, exactly as Darwin had predicted.
We must remember, however, that the organisms studied in this way are far from representative. They are in general the most successful members of animal associations living in very constant marine or lacustrine environments. We have not got similar data for land species… Nor do we possess them for the rarer forms. We shall see… that perhaps dominant species in a uniform environment are the least likely to undergo sudden change to a new type.”

J. B. S. Haldane book The Causes of Evolution

Introduction, p. 22.
The Causes of Evolution (1932)

“Throughout his last half-dozen books, for example, Arthur Koestler has been conducting a campaign against his own misunderstanding of Darwinism. He hopes to find some ordering force, constraining evolution to certain directions and overriding the influence of natural selection. […] Darwinism is not the theory of capricious change that Koestler imagines. Random variation may be the raw material of change, but natural selection builds good design by rejecting most variants while accepting and accumulating the few that improve adaptation to local environments.”

Stephen Jay Gould book The Panda's Thumb

"Double Trouble", pp. 38–40
The Panda's Thumb (1980)

“As we look around the organizational world we begin to see that it is possible to identify different species of organization in different kinds of environments. Just as we ﬁnd polar bears in arctic regions, camels in deserts, and alligators in swamps, we notice that certain species of organization are better ‘‘adapted’’ to speciﬁc environmental conditions than others. We ﬁnd that bureaucratic organizations tend to work most effectively in environments that are stable or protected in some way and that very different species are found in more competitive and turbulent regions, such as the environments of high-tech ﬁrms in the aerospace and microelectronics industries.”

Gareth Morgan book Images of Organization

Source: Images of Organization (1986), p. 39; As cited in as Vivien Martin -(2003) Leading change in health and social care. p. 157: About the organization as organism.

“Evolution must have involved the simultaneous change in many genes, which doubtless accounts for its slowness. Here matters would have been easier if heritable variations really formed a continuum, as Darwin apparently thought, i. e. if there were no limit to the possible smallness of a variation. But this is clearly not the case when we are considering meristic characters. …the atomic nature of Mendelian inheritance suggests very strongly that even where variation is apparently continuous this appearance is deceptive.”

J. B. S. Haldane book The Causes of Evolution

Source: The Causes of Evolution (1932), Ch. IV Natural Selection, pp. 103-104.