Darwin, Charles Robert

Darwin, Charles Robert

(b. The Mount, Shrewsbury, England, 9 February 1809; d. Down House, Downe, Kent, England, 19 April 1882)

natural history, geology, evolution.

Darwin was the fifth child and second son of Robert Waring Darwin, a successful and respected physician practicing in Shrewsbury, and Susannah Wedgwood, daughter of the potter Josiah Wedgwood I. The Darwin family was characterized by the high intellectual quality of its members, prosperity, industriousness, professional ability, and wide cultural interests.

Darwin’s education was begun by his elder sisters after the premature death of his mother. In 1817 he was sent to a day school at Shrewsbury, where he was found to be slow at learning. In 1818 he was entered at Shrewsbury School under Dr. Samuel Butler (grandfather of the author of Erewhon ). He afterwards complained he was taught nothing but classics, a little ancient history, and geography. “The school as a means of education to me was simply a blank.” This statement is perhaps unfair in that his grounding in the classics probably helped him afterwards to think so devastatingly straight. But his headmaster rebuked him publicly for wasting his time on chemical experiments, and his father upbraided him with the remark, “You care for nothing but shooting, dogs, and ratcatching, and you will be a disgrace to yourself and all your family.” He was removed from Shrewsbury School in 1825 and sent to Edinburgh University to study medicine.

Darwin stayed at Edinburgh until 1827, attending courses of lectures on materia medica, pharmacy, chemistry, and anatomy, which he found unbearably dull. But worst of all were his experiences attending operations, performed perforce without anesthetics. These repelled him to such an extent that he rushed out and vowed that medicine was no career for him. The chief advantages that he gained from his stay at Edinburgh were his friendship with Robert Grant, zoologist, who accepted Lamarck’s teachings on evolution; geological excursions with Robert Jameson; and expeditions onto the Firth of Forth to collect marine animals.

Confronted with the necessity of starting his son on a new line of endeavor, Darwin’s father sent him to Cambridge as a preparation for entering the Church of England as a clergyman. At that time, he accepted the Articles of Faith, and perfunctorily attended lectures, but his three years at Cambridge he thought “wasted as far as the academical studies were concerned, as completely as at Edinburgh and at school.” But he there made the acquaintance of Adam Sedgwick, who interested him in geology, and, most important of all, John Stevens Henslow, who fired him with a passionate interest in natural history and inspired him with a friendship that gave him confidence in himself, after his discouragement in his own family, at school, and at Edinburgh. Henslow acted as a second father to young Darwin during this critical, formative period in his life, which was climaxed by the voyage of the Beagle.

After taking a poor degree at Cambridge in 1831, Darwin was at home when he received an invitation, instigated by Henslow, to join the Admiralty survey ship H. M. S. Beagle, under the command of Robert FitzRoy, as unpaid naturalist on a voyage to survey the coasts of Patagonia, Tierra del Fuego, Chile, and Peru; to visit some Pacific islands; and to carry a chain of chronometrical stations around the world. Darwin wished to accept at once, but his father objected. Darwin’s uncle, Josiah Wedgwood II, thought the objection unreasonable and persuaded his brother-in-law to withdraw it. Darwin sailed on the Beagle on 27 December 1831.

The five years of the voyage were the most important event in Darwin’s intellectual life and in the history of biological science. Darwin sailed with no formal scientific training. He returned a hard-headed man of science, knowing the importance of evidence, almost convinced that species had not always been as they were since the creation but had undergone change. He also developed doubts of the value of the Scriptures as a trustworthy guide to the history of the earth and of man, with the result that he gradually became an agnostic. The experiences of his five years in the Beagle, how he dealt with them, and what they led to, built up into a process of epoch-making importance in the history of thought.

On 29 January 1839, Darwin married his first cousin, Emma Wedgwood, daughter of the Josiah Wedgwood who had saved his place in the Beagle. At first the young couple lived in London, but ill health began to attack Darwin shortly after his marriage. He found himself increasingly handicapped by great lassitude, nausea, and intestinal discomfort, which made it impossible for him to lead a normal life with social and academic contacts. The Darwins therefore moved to the country, fifteen miles from London, to Down House, in the village of Downe, in Kent. There Darwin had a garden, a small estate about which he could walk, spare rooms for the few friends who were occasionally invited to stay, a study where he could work, and peace and quiet.

His ill health gradually restricted him to a routine of four hours’ work a day, walks in the garden, visits to the greenhouses, occasional walks in the neighborhood or rides on a pony, interspersed with periods of rest on a sofa while reading a novel. Dinner was followed by listening to the piano and then early bed.

As his physicians could not discover any organic cause for Darwin’s ill health, the idea gained ground that he was a hypochondriac, and in recent years some psychiatrists have attempted to show that he was of a neurotic disposition, but the evidence is not wholly satisfactory. Following the suggestion of Saul Adler, a pathologist expert on South American infections, other commentators note that Darwin was heavily bitten in the Argentine by the Benchuca, the “black bug of the pampas,” Triatoma infestans, 70 percent of which are now reckoned to be vectors of Trypanosoma cruzi, the causative agent of Chagas’ disease. As this trypanosome was not discovered until 1909, Darwin’s doctors would have been unable to find an organic cause for his trouble; but the clinical picture found in sufferers from Chagas’ disease matches Darwin’s symptoms in detail. The parasite invades the muscle of the heart causing lassitude; it also invades the nerve cells of Auerbach’s plexus in the wall of the intestine, upsetting peristalsis; and it invades the auricular-ventricular bundle of the heart, interference with which may cause heart block. It has unpredictable periods of latency, after which it can be recovered from blood of patients infected many years before. Darwin suffered heart attacks and died from one. Whether in addition Darwin showed neurotic tendencies, accepting the overcare which his wife bestowed on him and taking advantage of his semi-invalidism to protect himself from the distractions of society and amusement, will never be known.

Darwin and his wife had ten children, of whom three died in infancy or childhood. The healths of the survivors (all of whom lived to ripe ages), and their launching in life, gave him anxiety. He once wrote that his chief worries were the discovery of gold in California and in Australia, “beggaring me by making my money on mortgage worthless”; the French coming by the Westerham and Sevenoaks roads, and, therefore, enclosing Down; and, third, “professions for my boys.” His fears were groundless. His investments were very profitable, Napoleon III did not invade England, and his sons made careers for themselves of which any father could be proud: Sir George Darwin, mathematician and astronomer; Sir Francis Darwin, botanist; Leonard Darwin, engineer and promoter of eugenics; and Sir Horace Darwin, scientific engineer and founder of the Cambridge Scientific Instrument Co. These men, their children and grandchildren, like their father and ancestors, provide material for Galton’s theory of the inheritability of intellectual eminence.

Darwin’s contributions to science fall into three main groups: geology, evolution and natural selection, and botany.

Darwin as Geologist. When Darwin sailed in the Beagle, the most commonly accepted theory in geology was that of catastrophism, which held that the forces which had produced change during the past history of the earth had been on a far greater scale than any which are active today. When geologists had concluded that stratified rocks had originated as beds of sediment laid down beneath the sea, they had then been obliged to explain how the sedimentary strata had been raised up from the sea bottom to form hills and mountains, and how they had been shifted from the horizontal position, in which they must originally have been deposited, to the inclined or even vertical positions in which they are now so often found. There were two possible explanations: (1) that the sea had formerly stood at a higher level and had in fact extended over the whole earth’s surface, or (2) that the strata had been upraised and disturbed. By 1831 most geologists had rejected the idea that the sea had formerly covered the whole earth, but when they tried to imagine forces capable of raising rock strata from the bottom of the sea to form hills or ranges of mountains, it seemed to them that such changes would necessarily involve tremendous convulsions of the earth’s surface. Furthermore, they saw a link between periods of convulsion and upheaval in the history of the earth and changes in animal life. They concluded, naturally, that a convulsion of the earth’s surface tended to destroy many species of animals and that when the convulsion had subsided new species were created to replace those that had been lost.

In the view of the catastrophists, there had been in the history of the earth a succession of creations of animal and plant life. Each creation had survived during a period of relative tranquillity of the earth’s surface, but had later been destroyed in a catastrophic disturbance and upheaval. The history of the earth therefore included periods of tranquillity interrupted by catastrophes, and each catastrophe was followed by a new creation. The catastrophic theory of geological history was reconciled to the account of creation in the Bible by supposing that the most recent catastrophe had been the flood of Noah. Many fossil animals were therefore characterized as antediluvian, or from before the flood. Geologists also supposed that the successive creations were of a progressively higher order which culminated finally in the creation of man.

Since the time of the flood the surface of the earth had been fixed, stable, and unchanging and the whole system of nature tranquil and orderly. The modern order of nature, catastrophists thought, was so very different from that which had existed throughout most of the history of the earth that little could be inferred of past events from present conditions.

The catastrophist viewpoint, firmly held by such English geologists as William Buckland, William Daniel Conybeare, and Adam Sedgwick, was challenged in 1830 by Charles Lyell in his Principles of Geology. Lyell had concluded that strata could be elevated from the bottom of the sea by the repeated action of earthquakes continued over long periods of time. In Italy and Sicily he had found recently elevated strata in the neighborhood of active volcanoes and in an area where severe earthquakes had occurred frequently throughout historic time. He showed to his own satisfaction that the strata had been elevated very gradually over an immense period of time, instead of by a single convulsion, and then went on to investigate how far the phenomena of geology might be explained by the various forces observable on the earth’s surface today. With great success he showed that the ordinary action of rain, running water, and the waves of the sea was sufficient to explain the wearing down of land and deposition of sediments, whereas the ordinary, long-continued action of volcanoes and earthquakes was sufficient to elevate continents and mountain ranges.

When Darwin sailed in the Beagle, he had with him the first volume of Lyell’s Principles of Geology (1830), which he had been advised to read but on no account to believe. That is, however, exactly what Darwin did, because he satisfied himself that Lyell’s views accorded with the facts: the first step in the making of a man of science possessed of critical judgment.

Santiago in the Cape Verde Islands provided Darwin’s first material for geological study. By applying Lyell’s principles, he quickly unraveled the history of the island. From the clear exposure of the rocks on the coast he saw that the oldest were crystalline and volcanic. Overlying them was a bed of limestone containing shells of marine organisms of Tertiary date, sixty feet above sea level and twenty feet thick. This bed, Darwin reasoned, had been deposited in a shallow sea and had since been raised to its present height; the island had undergone subsidence and then elevation. Above the limestone was more recent volcanic rock which had altered the uppermost limestone and baked it; evidence of metamorphism in situ.

St. Paul’s Rocks in mid-Atlantic enabled him to make acquaintance with an island which he correctly recognized as being of neither volcanic nor coralline origin; it is regarded today as an exposed portion of the mantle of the earth. But it was South America that presented itself as a model for his observational and interpretative skill. By comparing lavas of undoubted volcanic origin with igneous rocks of the Andes, he saw that they were closely related. He found that minerals in granites and in lavas were in all respects similar, and he showed a perfect graded series between crystalline granites and glasslike lavas. By observing the direction of strike and the angle of dip of strata, he found that the planes of foliation in schists and gneisses and the planes of cleavage in slates remained constant over areas stretching hundreds of miles, while their planes of inclination could vary greatly. Foliation planes and cleavage planes were parallel to the direction of the great axes along which elevation of the land had taken place. This was directly contrary to the then accepted views put forward by Sedgwick and by Lyell, and Darwin was able to prove that foliation and cleavage are not original phenomena dependent on the deposition of the strata, but had been subsequently superimposed on the beds by pressure, resulting in recrystallization in the case of foliation. He observed clay slate passing over into gneiss as it approached granite, which showed how homogeneous rocks could develop foliation by metamorphosis. Darwin’s demonstration of the origin of metamorphic rocks by deformation and of the distinction between cleavage and sedimentary bedding was a major contribution to geology.

The west coast of South America was an equally fruitful geological laboratory for Darwin. He was a witness to the earthquake that devastated Concepción and saw that it had resulted in an elevation of the land by several feet. He was further able to make out a connection between elevation of the land and neighboring volcanic activity because at the time when the land rose near Concepción a number of volcanoes in the Andes renewed their activity, and a new volcano beneath the sea erupted near Juan Fernandez. All these facts were shortly to be woven into an unexpected pattern.

By observing that the shells in beds raised to heights of as much as 1,300 feet belonged to species still living, and in proportions of species similar to those in the ocean, Darwin was able to prove, as Lyell had in Sicily, that such elevation was recent. In the Andes, at a height of 7,000 feet, he found a fossil forest of trees in situ (i. e., not drifted from elsewhere) because their trunks projected several feet perpendicularly from the stratum in which they were embedded, which was itself overlaid by thousands of feet of sedimentary deposits alternating with volcanic lavas. This showed that the trees had been buried thousands of feet beneath sea level as the deposits accumulated, and had since been raised to their present height. Here was proof of extensive subsidence as well as elevation.

Beds containing shells that had been raised up were far fewer and much less extensive than low-lying beds, and Darwin found that this was due to the erosion that constantly attacks land surfaces and destroys deposits. This fact had a bearing on estimations of the age of the earth, because while the time taken for a deposit to be formed can be roughly gauged, it is impossible to tell how long an interval of time has gone by while the beds were eroded. This means that the nonconformities between geological formations may represent much longer periods of time than the formation of the beds themselves, and that the age of the earth must be vastly greater than was then imagined.

From these findings, Darwin was led to consider what are the most favorable conditions for the accumulation of beds many thousands of feet thick containing fossils, such as are found elsewhere. He concluded that it could only have been when a slow subsidence continually lowered the bottom of a shallow sea, so that the depth of that sea below sea level remained fairly constant. These conditions further imply that such a sea was near to continental land, from which erosion brought down the material spread out in the deposits. Proof of this was obtained in observation of beds south of Valparaiso, 800 feet thick, containing shells of animals which when alive lived in shallow water, not more than 100 feet deep. The lowest beds of the deposit must have lain 700 feet higher than at present when the first shells became embedded, and as subsidence started the deposits continued and kept pace with the drop of 700 feet. Another bed showed evidence of the same process involving a subsidence and deposits of 6,000 feet. The various conditions required for such accumulations of fossils can only have been met occasionally and at particular localities in the history of the earth, from which it follows that the fossil record must be expected to be erratic and incomplete.

Another line of study to which Darwin was led by his expeditions in the Andes was the change in climate which regions must have undergone, both in geological time and during the life of man. This followed from observation of deserted houses, abandoned by Indians, up to the snowline in places now quite uninhabitable because of lack of water and fertility. This connection between geological phenomena and life was further developed in his studies of coral reefs.

While in South American waters, Darwin had never seen a coral reef, but he knew that atolls in their myriads all over the oceans are about at sea level, and that the coral polyps which build them can live only in waters less than 120 feet deep and at temperatures above 20°C. The theory of the origin of atolls, or lagoon islands, developed by Lyell, was that they were formed on the rims of submarine volcanic craters. Darwin quickly saw that such a hypothesis was untenable, and he put forward his own deductively. There must have been a foundation for the corals at a depth not exceeding 120 feet. It cannot be imagined that there were innumerable submarine mountain ranges with their summits all exactly at this height; therefore, they must have been brought to the required level by subsidence, and he found evidence for it in drowned villages in the Caroline Islands. This has since been confirmed by deep borings at Funafuti, at Bikini, and at Eniwetok, where evidence has been found of over 4,600 feet of coral rock produced by shallow-water organisms during prolonged subsidence.

In addition to atolls or lagoon-islands, there are also barrier reefs, like the Great Barrier Reef of Australia, which is known to have been erected by coral polyps on the down-faulted coastal edge of northeast Australia. Darwin observed a third type of coral reef, the fringing reefs or shore-reefs that surround an island which projects high above the sea, and these reefs are often found lifted above sea level. Fringing reefs are therefore the result of coral action on platforms that are either stationary or have undergone elevation. With all this evidence, Darwin drew a map. He found that large zones of the Pacific Ocean have atolls and barrier reefs and have undergone subsidence, while other zones, parallel to these, have fringing reefs and have undergone elevation. Now the most extraordinary correlation with these facts, bearing in mind Darwin’s observations of the connection between land elevation and volcanic activity, was the distribution of active volcanoes in the Pacific: all of them are situated in the zone of fringing reefs, not one of them in the zone of atolls or barrier reefs. Darwin’s book on Coral Reefs, published in 1842, still remains the accepted explanation, except for a slight addition in the form of R. A. Daly’s glacial control theory. This is based on the fact that during the recent Ice Ages, the amount of water immobilized in icecaps reduced the level of the oceans by 150 feet, which would have exposed the atolls to the air and cut down their height by wave-action. But when the Ice Age came to an end and the sea level rose again, the platforms were there for coral polyps to make new atolls.

The evidence which Darwin obtained in South America and in atolls for changes of sea level was later responsible for leading him into error. In 1838 in attempting to explain the Parallel Roads of Glen Roy in Scotland, Darwin imagined that the land had sunk by over 1,000 feet and that the so-called roads were marine beaches. In 1862 it was shown by T. F. Jamieson that the glaciers of Ben Nevis had dammed back the waters of a lake, the level of which dropped twice as outlets were formed, and that the roads were lake beaches. Darwin admitted defeat in words which have an important message for all scientific research workers: “How rash it is in science to argue because any case is not one thing, it must be some second thing, which happens to be known to the writer…. My error has been a good lesson to me never to trust in science to the principle of exclusion”.

Darwin’s trilogy of geological books was completed by the publication in 1844 of Volcanic Island, and at the end of 1846 by Geological Observations on South America. The supremacy of the position which geology occupied in Darwin’s mind shortly after his return from the voyage of the Beagle is shown by the order of subjects in the title of the first edition, published in August 1839, of his Journal of Researches into the Geology and Natural History of the Various Countries Visited by H. M. S. Beagle. In the second edition, published in August 1845, natural history and geology have changed places. The reason for this is to be found in the progressive orientation of Darwin’s mind toward the problem of evolution.

Evolution and Natural Selection. When Darwin sailed in the Beagle, he had no reason to call in question the accepted view that the species of plants and animals alive on earth were as they had always been since the creation. It was only gradually that doubts began. They arose from four kinds of evidence. The first was that in some areas species had become extinct. Darwin himself had found gigantic fossil armadillos (and other forms) in South America; but armadillos of similar but not identical form also live in South America. This meant that “extinct animals have a close relation in form with extinct species.” Why was this?

Second, in adjacent areas of South America, Darwin found one species replaced by different, although very similar, species. On the pampas he observed and collected specimens of the South American ostrich (rhea), but when he went farther south into Patagonia, he found a very similar but smaller species (Rhea darwinii ). But why were the two species of rheas built on the same plan, different from that of the African ostriches? Why were the agoutis and vizcachas of South America built on the same plan as other South American rodents and not on that of North American or European hares and rabbits?

The third doubt was evoked by the fact that inhabitants of oceanic islands tended to resemble species found in the neighboring continents; African-like species in the Cape Verde Islands, South American-like species in the Galápagos archipelago. At the same time, although the geological and physical features of the Cape Verde and Galápagos Islands are very similar, their faunas are quite different. Why was this?

Finally, the different Galápagos islands, identical in climate and physical features, and very close to each other, might be expected to have identical species, but they had not. On different islands he observed that the finches characteristic of the Galápagos group differed in structure and food habits. Some ate insects, others ate seeds, and their sizes and their bills differed in relation to their diets and mode of life. Darwin suspected that they were only varieties of a single species. The local inhabitants could also tell at sight from which island any of the giant tortoises had come. Was all this arbitrary and meaningless or could a pattern of meaning be discerned?

The answer gradually came to Darwin: All these questions, and many more, could be rationally answered if species did not remain immutable but changed into other species, and diverged, so that one species could have given rise to two or more. It is because they had a common ancestor in South America that fossil armadillos resemble living armadillos, that agoutis resemble capybaras, and that the Galápagos birds resemble South American birds, while the Cape Verde birds resemble African birds with which in each case they had a common ancestor. But why did the finches and other birds of each Galápagos island differ from one another? “One might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends,” Darwin wrote. These “ends” are very important; they fit the animals for their mode of life, they are adaptations; and the isolation of each species on each island plays an important part.

Gradually, only a few months after his return to England, these ideas began to crystallize in Darwin’s mind: “Animals, our fellow brethren in pain, disease, death, suffering and famine—our slaves in the most laborious works, our companions in our amusements—they may partake of our origin in one common ancestor—we may be all netted together.”

In July 1837 Darwin started writing down his ideas at random in his Notebook on Transmutation of Species. He soon found that if change of species had occurred, there was a ready explanation for a number of otherwise arbitrary and inexplicable facts. Why are the bones of the arm of a man, the foreleg of a dog and a horse, the wing of a bat, and the flipper of a seal built on the same general plan, with the different bones corresponding, each to each? Why are young embryos of lizards, chicks, and rabbits so similar to each other, while their adults are so distinct? Why do some animals have useless rudiments of organs? Why do particular regions of the earth have their characteristic plants and animals? Why do organisms fall into groups, namely, species, that may be arranged in larger groups, namely, genera, that in turn may be arranged in still larger groups, namely, families, and so on? Why is there this apparent relationship of species instead of a random distribution of forms across the whole field of possibilities? Why do more or less similar organisms behave in similar ways? For instance, why do both horses and men yawn; why do both orangutans and men show emotional distress by weeping? Why do fossils in early geological formations differ greatly from those living today, while those from more recent formations differ only slightly?

All these questions could be meaningfully answered if species were related by descent from common ancesters, but not otherwise. It is important to note Darwin’s form of argument. He never claimed to demonstrate the change of one species into another, and in his letters constantly repeated that he was tired of impressing this fact on his readers and critics; all that he claimed was that if evolution has occurred, it explains a host of otherwise inexplicable facts. But after he had satisfied himself that evolution had occurred, he kept his views to himself because he saw the great obstacles that lay ahead. Evolution he already saw as the change that species undergo in relation to their adaptation to their environment. A woodpecker differs from other birds in that it has two claws of its feet directed backward, with which it secures a firm grasp on the trunk of a tree, stiff tail feathers with which it supports itself against the tree, a stout bill with which it chisels a hole in the bark, and a very long tongue which it projects through the chiseled hole to extract the grubs beneath the bark. The woodpecker must have evolved these adaptations. How?

In considering this question of how evolution might have occurred, Darwin noticed that the cultivation of plants and the domestication and breeding of animals, both of which man has practiced since the Neolithic period, were the result of selection. Man deliberately chose the parents of the next generation of his plants and animals, to perpetuate and improve the qualities in them which he required. But how did, or could, selection operate in nature, where there had been no man to direct it, since the beginning of life on earth? Darwin had already observed that some species are better adapted than others to life in particular environments, and thus are likely to leave more descendants, while the less well adapted may diminish and become extinct (Notebook 1, MS. p. 37, notebook finished in February 1838). In other words, he had already grasped the principle of natural selection before he saw how it was enforced in nature.

The solution to this problem came to him on 28 September 1838 when he read Thomas Robert Malthus’ Essay on the Principle of Population. Malthus, whose whole line of thought was tinged with opposition to the principles of egalitarianism displayed by the French Revolution, argued that since the potential rate of increase in man was geometrical, and that his population could double in twenty-five years, while the increase of available foodstuffs could not increase so fast, there was bound to be misery, poverty, starvation, and death among the poor unless the rate of population increase in man was checked by war, famine, disease, or voluntary restraint (which would diminish the incentive to work among the poor).

Malthus, therefore, demonstrated the relentless pressure which human populations, by their boundless tendency to grow, maintain on their requirements for life whatever the level of their resources may be. If the food supply and other requirements for life can be increased, a population will tend to grow until its growth presses against the limits of the enlarged supply of food. Malthus also observed that in many countries the population did not grow and much of his book is taken up with a study of the means by which the numbers of people were limited in different countries. These ranged from exposure of infants, infanticide, and the intermittent reduction of the population by famine in China, to delayed marriage and strict sexual morality in Norway. But Malthus was able to show that in every country the tendency of a human population to grow was under some form of severe and continued restraint.

Darwin pounced on the argument and applied it, not to man, but to plants and animals in nature, and saw that they are in no position to increase their food supplies, but must die if they outstrip them by their own numbers. Here were the sanctions that made natural selection work.

Like most flashes of genius, it was very simple, and T. H. Huxley said later, “How extremely stupid not to have thought of that.” It marked a turning point, not only in the history of science, but in the history of ideas in general, for there is no field of human intellectual endeavor that has not been influenced by the thought and fact of evolution. By good fortune, the note that Darwin scribbled down immediately when the flash struck him has been preserved. It is of such importance that it deserves quotation:

28th [September 1838] We ought to be far from wondering of changes in numbers of species, from small changes in nature of locality. Even the energetic language of De Candolle does not convey the warring of species as inference from Malthus. Increase of brutes must be prevented solely by positive checks, excepting that famine may stop desire. In Nature production does not increase, whilst no check prevail, but the positive check of famine and consequently death. I do not doubt every one till he thinks deeply has assumed that increase of animals exactly proportionate to the number that can live.

Population is increase at geometrical ratio in FAR SHORTER time than 25 years, yet until the one sentence of Malthus no one clearly perceived the great check amongst men. There is [a] spring, like food used for other purposes as wheat for making brandy. Even a few years plenty makes population in man increase and an ordinun crop causes a dearth. Take Europe, on an average every species must have same number killed year with year by hawks, by cold etc. even one species of hawk decreasing in number must affect instantaneously all the rest. The final cause of all this wedging, must be to sort out proper structure, and adapt it to changes, to do that for form which Malthus shows is the final effect (by means however of volition) of this populousness on the energy of man. One may say there is a force like a hundred thousand wedges trying to force every kind of adapted structure into the gaps in the oeconomy of nature, or rather forming gaps by thrusting out weaker ones.

This passage, in which Darwin’s thought penetrates through a jungle of ideas, following on his reading of Candolle’s description of the war of nature and Malthus’ book, is remarkable for a number of reasons. In the first place it pinpoints the notion that evolution does not take place in a vacuum, but each individual, if it is lucky, lodges in its fortified position in the economy of nature, in what is now called its ecological niche, in dynamic equilibrium not only with the physical factors of the environment, but with the other living organisms of the habitat. It is because Darwin recognized this fact so clearly that he can be reckoned as the founder of the science of ecology.

Second, this passage shows that evolution is not a process that goes on in single individuals, or even in Paris, but which proceeds in populations and consists of some individuals becoming better adapted, under the pressure of natural selection, which is the third lesson of this passage. Ernst Mayr has pointed out that one of the most important recent advances in biology has been the realization that the real units are populations, which have objective existence, and not types (which are only imaginary abstractions), and that Darwin was more responsible than anyone else for the substitution of “population-thinking” for “typological thinking.” The change to a different species is nothing but a by-product of the process of a species becoming better adapted, after a certain point of divergence has been reached. The explanation of the fact of divergence itself is foreshadowed in the passage. As Darwin later wrote, “The more diversified the descendants of any one species become in structure, constitution and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature.” Again, it is the ecological niches which supply the key to the problem.

Darwin’s argument can be formulated as follows: (1) The numbers of individuals in species in nature remain more or less constant. (2) There is an enormous overproduction of pollen, seeds, eggs, larvae. (3) Therefore, there must be high mortality. (4) All individuals in a species are not identical, but show variation and differ from one another in innumerable anatomical, physiological, and behavioristic respects. (5) Therefore, some will be better adapted than others to their conditions of life and to the ecological niches which they could occupy, will survive more frequently in the competition for existence, will leave more off-spring, and will contribute most of the parents that will produce the next generation. (6) Hereditary resemblance between parents and offspring is a fact. (7) Therefore, successive generations will not only maintain but improve their degree of adaptation to their modes of life, i.e., to the conditions of their environments, and as these conditions vary in different places, successive generations will not only come to differ from their parents, but also from each other and give rise to divergent stocks issuing from common ancestors.

This is the formal theory of evolution by natural selection, which recent observation and controlled experiment have proved to be correct in all cases. What modern biology has done is to provide answers to the two questions which, in the state of knowledge of his time, Darwin could not answer: what is the nature of hereditary transmission between parents (and grandparents, and so forth) and offspring? And what is the nature of the origin of heritable variation? Without heritable variation, natural selection could achieve nothing. In Darwin’s day, no clear distinction was made between what was heritable and what was not, and few doubted the inheritance of characters acquired by a parent during its own life.

The problem was completely solved (unknown to Darwin, or to the world before 1900) by Gregor Mendel, who proved that the basis of inheritance takes the form of particulate characters, distributed between parents and offspring in accordance with a simple law (since proved by cytology and the behavior of chromosomes) known as Mendel’s law of segregation. The inception of a heritable novelty was a sport, now known as a mutation, a random, nonadaptive change in the chemical structure of a particular character, now known as a gene. The application of Mendelian genetics to Darwinian selection was effected by the work of J. B. S. Haldane and Sir Ronald Fisher by 1930. Since then the synthetic theory of evolution by natural selection has been generally accepted by biologists. It is remarkable that even without the knowledge that these advances represent, to say nothing of those achieved in comparative biochemistry, serology, parasitology, and cytogenetics, Darwin was nevertheless able to construct a coherent theory which made general acceptance of evolution possible—and a mechanism to account for it, namely, natural selection. Although long considered inadequate, natural selection is now proved to be the basis for biological change and for the production of all the diverse structures and functions of living organisms.

Shortly before Darwin died, his son Leonard asked him how long he thought that it would be before positive evidence of natural selection would be forthcoming. Darwin replied, about fifty years. It was a remarkably accurate forecast, for it was in the 1930’s that Sir Ronald Fisher showed how expression of a gene, in the form of the bodily character that it controls, is itself the effect of selection. Shortly afterward, E. B. Ford demonstrated that mimetic resemblance in butterflies is adaptive, confers survival value, and originates from heritable variation. The researches of H. B. D. Kettlewell on industrial melanism in moths, P. M. Sheppard and A. J. Cain in snails, T. Dobzhansky on geographical races of fruit flies, and A. C. Allison on sickle cell in man have provided experimental evidence not only of natural selection but of the pressure at which it works, and have permitted actuarial estimates of the longevity of different genetic types. This follows the mathematical studies of Sir Ronald Fisher, Sewall Wright, and J. B. S. Haldane on the effects of selection at different intensities on the composition of populations.

Studies on what B. Rensch has called “ring-races” has shown species in the act of splitting into new species, in gulls, tits, and salamanders, when geographical isolation of portions of populations enables them to evolve independently of each other, so that they become adapted in different directions and eventually no longer interbreed. This speciation is what T. H. Huxley regarded as necessary for the final confirmation of Darwin’s views.

Paleontology has been a trap for biologists and others who have neglected David Hume’s warning that the existence of a state of affairs does not in itself justify conclusions on how it came about.

Darwin claimed that the fossil record, as known to him, was compatible with evolution; but that if fossils ever provided any evidence contrary to his theory, such, for instance, as to prove that the Cambrian fossils were the first organisms that ever lived, or that a mammal was “created” later than those earliest known mammals of the Stonesfield Slate of the Jurassic period, his theory of evolution must be abandoned. However, he never adduced any evidence from fossils to bear on the problem of the principle of natural selection.

Although the recognition of fossils as former living beings goes back four centuries, it is only recently that paleontology has come into its own as a science, largely as a result of the researches of George G. Simpson. Fully aware that the mechanism of evolution can be interpreted only in terms of genetics, ecology, selection, and population studies, Simpson has shown that evolutionary sequences previously claimed as “straight” are not straight at all. For example, the evolutionary history of the horse has followed a zigzag course, first in the direction of many-toed browsers on leaves, then in that of many-toed grazers on grass, and finally in that of one-toed grazers on grass. In general the horse increased in size, but some species became smaller. Each lap of the course can be correlated with the environmental conditions of the period: soft or hard ground, leafy or grassy (siliceous) vegetation. At all times the trend has been toward favorable adaptations, to ecological niches which paleontologists are now in a position to describe; in other words, it has been compatible with the requirements of natural selection and has been opportunistic and devoid of any predetermined program. Furthermore, the rate of evolution, now measurable by radioactive dating, is not correlated with variability, nor with fertility (years per generation). In this manner, Simpson has been able to show that natural selection under changing environmental conditions accounts for evolution, and explains why in terrestrial forms evolution has generally been rapid, while in marine forms it has been slow or stationary.

It is regrettable that Darwin in later years allowed himself to be persuaded to accept Herbert Spencer’s inappropriate expression “survival of the fittest.” This stresses survival when the important thing is the greater fecundity of the better adapted; it emphasizes a superlative “fittest” when it is the slightest comparative superiority of adaptation that confers advantage. It lays the subject open to the taunt of tautology: Who survive? The fittest. Which are the fittest? Those who survive. This is a form of argument which neglects entirely the fundamental fact that forms better adapted to their environment leave more offspring. Finally, the phrase conveys no inkling that the automatic choice exerted by nature in ramming the better adapted variants into their ecological niches is the efficient cause of adaptation. It was not the first (or last) time that so-called philosophers of science have encumbered scientists with their help.

After Darwin had developed his new theory of the origin of species by natural selection in 1838, he did not publish it, or even discuss it with his friends. In 1842 he drew up a rough sketch of his argument, which in 1844 he expanded into an essay but never published. In 1845 when he had finished preparing for publication the results of his geological work on the Beagle voyage, he put the species question aside and started on eight tedious years’ study of the structure and classification of living and fossil barnacles. In the course of this work he acquired firsthand knowledge of the amount of variation that is found in nature, and he also made a striking discovery, that of complemental males, small parasitic males found under the mantle of larger hermaphrodite or female individuals.

After his return to England in 1836 Darwin became close friends with Charles Lyell and Joseph Dalton Hooker. They did not accept evolution, which was known to them only in the form of Lamarck’s exposition. Lamarck’s views were in many ways similar to those of Erasmus Darwin, who posited that there was a “natural tendency” to perfection, and the “inner a feelings” of an animal caused it to provide the organs required to meet its needs. In 1844 Robert Chambers published Vestiges of the Natural History of Creation, which only brought the subject into disrepute by its amateurish ignorance.

In April 1856 Darwin described his theory of natural selection to Lyell, who urged him to write a book describing his views on species. He began the work in the summer of 1856. On 18 June 1858 Darwin received a letter from Alfred Russel Wallace containing a perfect summary of the views which he had worked out during the preceding twenty years. Thanks to Lyell and to Hooker, Darwin’s and Wallace’s papers were read together before the Linnean Society of London on 1 July 1858 and published on 20 August of that year.

Darwin then set about writing an “abstract” of his larger work, and On the Origin of Species was published on 24 November 1859. The fat was then in the fire. Old-fashioned biologists protested that Darwin indulged in hypotheses that he could not prove (and he did not pretend to prove them). Theologians were aghast at two consequences of Darwin’s work; the first was that man and the apes must have had a common ancestor, which dislodged man from his privileged position as created by God in his own image. The second arose from the consideration that if Darwin’s views on the origins of plants and animals, including man, by natural selection were true, then much of the argument for the existence of God based on the presence of design in nature was destroyed. The theologian William Paley had argued that highly specialized and coordinated adaptations, such as the tongue, beak, claws, and tail of the woodpecker, or the human hand, manifested a complex design which required one to postulate the presence of a designer in nature. If, however, these same adaptations could be accounted for by natural selection acting on random variations, a designer was no longer needed. Since natural theology, as represented by Paley, had enjoyed enormous influence in England, the destruction of its very foundations was greeted with dismay and outrage.

Matters came to a head at the celebrated Oxford meeting of the British Association for the Advancement of Science on 30 June 1860, when the Reverend Samuel Wilberforce, bishop of Oxford (who knew little of natural history but was coached by the anatomist Richard Owen, who was jealous at what he felt already was Darwin’s ascendancy over himself), twitted Darwin’s friend Thomas Henry Huxley with the question whether it was through his father or his mother that he claimed descent from an ape. Huxley replied that he was not ashamed to be descended from an ape but he would be ashamed of an ancestor who used great gifts and eloquence in the service of falsehood. Wilberforce was annihilated by Huxley and Hooker, and Darwin’s views on evolution started their conquest of the world. In the United States, Darwin’s friend, the botanist Asa Gray, had already won a victory over the anatomist and paleontologist Louis Agassiz, who was never able to accept Darwin’s theory.

After the Origin of Species, Darwin wrote three more books expanding different aspects of the work. The Variation of Animals and Plants Under Domestication (1868) took up in detail that subject which had been confined to one chapter of the Origin. It contained his hypothesis of pangenesis, by means of which Darwin tried to frame an explanation of hereditary resemblance, inheritance of acquired characters, atavism, and regeneration. It was a brave attempt to account for a number of phenomena which were beyond the bounds of scientific knowledge in his day, such as fertilization by the union of sperm with egg, the mechanism of chromosomal inheritance, and the development of the embryo by successive cell division. His hypothesis of pangenesis could not therefore give a permanently acceptable account of the multitude of phenomena it was designed to explain. It was, however, a point of departure for particulate theories of inheritance in the later nineteenth century.

Darwin’s next book, The Descent of Man (1871), filled in what was only adumbrated in the Origin. T. H. Huxley and W. H. Flower had shown already that the body of man differs less from that of an ape than the latter does from that of a monkey. It is important to remember that Darwin never claimed that man was descended from apes, but that man’s ancestor, if alive today, would be classified among the Primates, and would be even lower in the scale than the apes. Man and apes are subject to similar psychological and physiological processes in courtship, reproduction, menstruation, gestation, birth, lactation, and childhood. At early stages of embryonic development the human fetus has a tail, inherited from ancestors who not only had a tail as embryos but also as adults and were quadrupedal. Darwin wrote, “The time will before long come when it will be thought wonderful, that naturalists, who were well acquainted with the comparative structure and development of man and other animals, should have believed that each was the work of a separate act of creation.”

Having proved his point with man’s body, Darwin then turned to the most difficult aspect, man’s mind. Here he showed that the gap, however enormous between man and the highest animal, is not unbridgeable, by the principle of gradation. Man shares with animals the urge to self-preservation, sexual love, maternal affection, paternal protection, and the senses of pleasure, pain, courage, pride, shame, excitement, boredom, wonder, curiosity, imitation, attention, and memory. As for the moral sense, Darwin concluded that it, also, arose gradually, through evolution, and that any animal endowed with social instincts, which man’s ancestors undoubtedly possessed, would acquire a moral sense as soon as its intellectual powers had developed (by natural selection) to an extent comparable with those of man and was able to appreciate the survival value of collaboration and mutual affection. Borrowing from Marcus Aurelius the view that social instincts are the prime principles of man’s moral constitution, Darwin concluded that these, with the aid of intellectual powers and the effects of new tradition and habits, would lead naturally to the Golden Rule: “As ye would that men should do to you, do ye to them likewise.”

In this book Darwin added an essay on a related subject: sexual selection, the preferential chances of mating that some individuals of one sex (usually the male) have over their rivals because of special structures, colors, and types of behavior used in courtship displays, leading them to leave more offspring and accentuate their characters: for example, antlers in deer, trains in peacocks, feathers in birds of paradise, color in sticklebacks. There is no need to assume a power of aesthetic choice in either sex; the characters act as sexual stimulants, real aphrodisiacs, so that mating follows more quickly, occurs more often, and there are more progeny. In man, there can be no doubt that the differences between the sexes in respect of distribution of hair on face and body and of fat in local accumulations under the skin are the result of sexual selection.

Darwin did not explain how the preference of females for particular structures, colors, and courtship displays was related to natural selection, although female preferences themselves must be subject to natural selection. Perhaps Darwin’s greatest contribution in this area was to show that secondary sexual characteristics had evolved in relation to a complex pattern of reproductive behavior, which must itself be the product of natural selection.

The last of Darwin’s books in this series, The Expression of the Emotions in Man and Animals (1872), contains studies of facial muscles and means of expression in man and mammals, emission of sounds, erection of hair, and so forth, and their correlation with suffering, sobbing, anxiety, grief, despair, joy, love, devotion, reflection, meditation, sulking, hatred, anger, pride, disdain, shame, surprise, fear, horror, acceptance (affirmation), and rejection (negation). With this book Darwin founded the study of ethology (animal behavior) and conveyance of information (communication theory) and made a major contribution to psychology.

Botanical Works. From the first Darwin interested himself in adaptations of plants to cross-pollination. He found that trees (with countless flowers) tend to have flowers of one sex, while small plants have hermaphrodite flowers, and he showed that the unisexuality of trees would tend to prevent self-pollination. He concluded that “flowers are adapted to be crossed, at least occasionally, by pollen from a different plant.” Here was a general principle which must have a wide meaning, and he set out to study it. His attention was first directed to orchids, which have elaborate adaptations for cross-pollination, making the bees that visit their flowers carry away the pollen sacs with them and pollinate the next flowers that they visit. His book on the Fertilization of Orchids (1862) showed that plants are in no way behind animals in the marvels of the adaptations that they show. Darwin further observed that flowers that are pollinated by wind have no colors; it is only those that are pollinated by insects that have bright colors in their petals and sweet-smelling nectaries.

Presently Darwin noticed that in some species flowers differ by the lengths of their anthers and styles, like the primroses, which show two conditions, or loosestrife, which shows three. This is also an adaptation for cross-pollination, and these observations formed the basis of Different Forms of Flowers on Plants of the Same Species (1877). The problem continued to fascinate him, and he raised two large beds of seedlings of Linaria vuglaris, the one cross-pollinated and the other self-pollinated, all from the same plant. “To my surprise, the crossed plants when fully grown were plainly taller and more vigorous than the self-fertilized ones.” Darwin had experimentally discovered and demonstrated the fact of hybrid vigor, or heterosis, which is completely explained by Mendelian genetics. These experiments, conducted over twelve years on fifty-seven species, led to the publication of Effects of Cross and Self Fertilization (1876). The demonstration of the advantage that accrues from cross-fertilization explains not only why sexual reproduction (as distinct from asexual budding) increases heritable variation (through recombination of genes), but also reveals the basis for the survival value conferred by the existence of different sexes in a species. This adaptation (for that is what it is) is a very old one, for it was inherited by plants and animals before they diverged from one another.

Darwin’s interest in climbing plants was not that of a systematic botanist but an attempt to discover what adaptive value the habit of climbing has. He found that “climbing” is a result of the process of nutation; the apex of the plant’s stem bends to one side while it grows and the plane of the bend itself revolves, clockwise or counterclockwise, so that the apex describes circular sweeping movements. In the hop plant—in hot weather, during daylight hours—it takes a little over two hours for each revolution. If the growing stem hits nothing, it continues to circle; if it hits an object it wraps itself around it by twining, Twining thus enables a young and feeble plant, in one season, to raise its growing point and leaves much higher from the ground, with more exposure to sunlight and air, without expending time and energy in the synthesis of woody supporting tissues. There is a further delicate adaptation here; a twining plant will not twine around an object larger than approximately six inches in diameter. This adaptation prevents it from climbing up a large tree, where it would be deprived of air and sun by the tree’s own leaves.

Some plants climb by a modification of this method and have stalks and leaves that clasp other objects, and intermediate forms show that leaf-climbers evolved from twiners. In others, such as the Virginia creeper, the leaf tendrils end in little discs full of resinous fluid which anchor the plant to its support. These researches were described in Climbing Plants (1875).

The behavior of climbing plants and the bending of their shoots led Darwin to investigate the mechanical cause of such bending. The fact that a stem bends toward the light because it grows faster on the unilluminated than on the illuminated side of the stem had been known for some time. By means of simple but ingenious experiments, Darwin showed that the tip of the shoot was sensitive to light and that the bending was caused by growth of the stem on the side away from the light but some way down from the apex. Furthermore, this growth was due to a substance that comes down from the apex, “some matter in the upper part which is acted upon by light, and which transmits its effects to the lower part.” From these researches and experiments (reported in Power of Movement in Plants, 1880) has sprung the whole science of growth hormones in plants.

Darwin’s chance observation of the number of flies caught on the leaf of the common sundew (Drosera rotundifolia ) was the starting point for a series of observations and experiments which showed not only how insects are caught, but how their bodies are digested and ingested, and what the significance of this carnivorous habit is for the life of the plant. By feeding one bed of sundew plants with meat and depriving another bed, he found that the fed plants had larger leaves, taller flowerstalks, and more numerous seed capsules. This remarkable adaptation, which insures survival of the plants, explains why sundew plants, which have very few roots, through which only small supplies of nitrogen can be obtained, can live on extremely poor soil. Darwin was particularly impressed by the fact that the living cells of plants possess a capacity for irritability and response similar to that of the nerve and muscle cells of animals. His work on Insectivorous Plants was published in 1875.

Darwin’s last book connected with plants was The Formation of Vegetable Mould Through the Action of Worms (1881). This was published only six months before his death but covers a subject that he had studied for more than fifty years. He showed the services performed by earthworms in eating leaves and grinding earth in their gizzards and turning it into fertile soil, which they constantly sift and turn over down to a depth of twenty inches from the surface, thereby aerating it. He calculated from the weight of worm-castings that on one acre in one year’s time eighteen tons of soil are brought up to the surface by worms. This was a pioneer study in quantitative ecology.

Darwin was elected to fellowship of the Royal Society in 1839 at the age of twenty-nine; three foreign universities awarded him honorary doctorates; and fifty-seven leading foreign learned societies elected him to honorary or corresponding membership—the French Academy of Sciences only in 1878, for his views have never been really appreciated in France. The Prussian government awarded him the highly coveted Ordre pour le mérite, but from the British sovereign and the British government he never received any recognition. His demonstration of the fact of evolution, and of the automatic mechanism of natural selection which causes it, was unpalatable to the orthodox views of the Church of England. When he died, however, twenty members of Parliament asked the dean of Westminster to allow his burial in Westminster Abbey, an honor which was readily granted. Darwin himself would have been highly amused, for, with his genial sense of humor he once said, “Considering how fiercely I have been attacked by the orthodox, it seems ludicrous that I once intended to be a clergyman.” At his funeral there were present not only his friends Hooker, Huxley, and Wallace, but also James Russell Lowell, the American ambassador, as well as diplomats representing France, Germany, Italy, Spain, and Russia.

BIBLIOGRAPHY

I. Books. Journal of Researches into the Geology and Natural History of the Various Countries Visited by H. M. S. Beagle (London, 1839); facs. repr. (New York, 1952); 2nd ed., Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage of H. M. S. Beagle (London, 1845); repr., intro. by Sir Gavin de Beer (New York, 1956); The Structure and Distribution of Coral Reefs (London, 1842; 2nd ed., 1874); Geological Observations on the Volcanic Islands Visited During the Voyage of H. M. S. Beagle (London, 1844); Geological Observations on South America (London, 1846); A Monograph of the Subclass Cirripedia, 2 vols. (London, 1851, 1854); A Monograph of the Fossil Lepadidae, or Pedunculated Cirripedes of Great Britain (London, 1851); A Monograph of the Fossil Balanidae and Verrucidae (London, 1854); On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (London, 1859; 2nd ed., 1860; 3rd ed., 1861; 4th ed., 1866; 5th ed., 1869; 6th ed., 1872); repr., intro. by Sir Gavin de Beer (London, 1963); 1st American ed. (New York, 1860); variorum text, Morse Peckham, ed. (Philadelphia, 1959); facs. repr. of 1st ed. (Cambridge, Mass., 1964); On the Various Contrivances by Which British and Foreign Orchids are Fertilized by Insects, and on the Good Effects of Intercrossing (London, 1862, 2nd ed., 1877); The Variation of Animals and Plants Under Domestication (London, 1868; 2nd ed., 1875); The Descent of Man, and Selection in Relation to Sex (London, 1871; 2nd ed., 1874); The Expression of the Emotions in Man and Animals (London, 1872); Insectivorous Plants (London, 1875); Climbing Plants (London, 1875); The Effects of Cross and Self Fertilization in the Vegetable Kingdom (London, 1876); The Different Forms of Flowers on Plants of the Same Species (London, 1877); The Power of Movement in Plants, assisted by Francis Darwin (London, 1880); The Formation of Vegetable Mould, Through the Action of Worms, With Observations on Their Habits (London, 1881); repr., intro. by Sir Albert Howard (London, 1961); and a preliminary notice in Ernst Krause, Erasmus Darwin, W. S. Dallas, trans. (London, 1879).

Posthumously published writings include Life and Letters of Charles Darwin, Francis Darwin, ed. (London, 1887); Autobiography (London, 1887), unexpurgated ed., Nora Barlow, ed. (London, 1958); More Letters of Charles Darwin, Francis Darwin and A. C. Seward, eds. (London, 1903); “Sketch” of 1842 and “Essay” of 1844, in Evolution by Natural Selection, foreword by Sir Gavin de Beer (Cambridge, 1958); and the notebooks on transmutation of species, Sir Gavin de Beer, ed., in Bulletin of the British Museum (Natural History ), Historical Ser., 2 (1960), 23–200, and 3 (1967), 129–176.

II. Bibliographies. Handlist of the Darwin Papers at the University Library Cambridge (Cambridge, 1960); R. B. Freeman, The Works of Charles Darwin. An Annotated Bibliographical Handlist (London, 1965).

III. Secondary Literature. See Sir Gavin de Beer, “Darwin’s Views on the Relations Between Embryology and Evolution,” in Journal of the Linnean Society of London, 66 (1958), 15–23; “The Origins of Darwin’s Ideas on Evolution and Natural Selection,” in Proceedings of the Royal Society, 155B , 321–338; “Mendel, Darwin, and Fisher,” in Notes and Records of the Royal Society, 19 (1964), 192–226; 21 (1966), 64–71; Atlas of Evolution (London, 1964); and Charles Darwin. A Scientific Biography (New York, 1965).

Also of interest are W. E. Le Gros Clark, Man-Apes or Ape-Men? (New York, 1967); A. Cronquist, The Evolution and Classification of Flowering Plants (London, 1967); T. Dobzhansky, Genetics and the Origin of Species (New York, 1937; 4th ed., 1959); Mankind Evolving (New Haven, 1962); R. A. Fisher, The Genetical Theory of Natural Selection (Oxford, 1930); E. B. Ford, Ecological Genetics (New York, 1964); Bentley Glass, Owsei Temkin, and William R. Strauss, eds., Forerunners of Darwin (Baltimore, 1959); Gerald L. Geison, “Darwin and Heredity: the Evolution of His Hypothesis of Pangenesis,” in Journal of the History of Medicine, 24 (1969), 375–411; Michael T. Ghiselin, The Triumph of the Darwinian Method (Berkeley, 1969); John C. Greene, The Death of Adam. Evolution and Its Impact on Western Thought (Ames, Iowa, 1959); J. B. S. Haldane, The Causes of Evolution (London, 1932); Garett Hardin, Nature and Man’s Fate (London, 1960); Julian Huxley, A. C. Hardy, and E. B. Ford, eds., Evolution as a Process (London, 1954); Julian Huxley, Evolution. The Modern Synthesis (London, 1942; repr., 1963); Ernst Mayr, Animal Species and Evolution (Cambridge, Mass., 1963); Milton Millhauser, Just Before Darwin. Robert Chambers and Vestiges (Middletown, Conn., 1959); Bernard Rensch, Evolution above the Species Level (London, 1959); and Anne Roe and George Gaylord Simpson, eds., Behavior and Evolution (New Haven, 1958).

See also George Gaylord Simpson, The Meaning of Evolution. A Study of the History of Life and of its Significance for Man (London, 1950); Horses. The Story of the Horse Family in the Modern World and Through Sixty Million Years of History (New york, 1951); The Major Features of Evolution (New York, 1953); This View of Life. The World of an Evolutionist (New York, 1964); The Geography of Evolution (Philadelphia-New York, 1965); G. Ledyard Stebbins, Variation and Evolution in Plants (New York, 1957); and Sol Tax, ed., Evolution After Darwin, 3 vols (Chicago, 1960).

On Darwin’s health see Saul Adler, “Darwin’s Illness,” in Nature, 184 (1959), 1102–1103.

Gavin de Beer