Darwin’s Ideas on Evolution – His World Trip and Finches – Modern Synthesis of Evolution -His Religious Views

Summary of Darwin’s main work on evolution: Natural Selection

(This section by OHEA Vice President who has a Ph.D. in the Biological Sciences)


Young Charles Darwin, portrait by George Richmond

“Population” is key term in evolutionary biology. A population is simply all the individuals of a species in a given area that are likely to be breeding with each other. A feature of natural populations is that every population of animals and plants produces more progeny than its environment can support. There is not enough food, shelter, water, nesting materials, general space, etc. for all individuals so they compete for these items. Variation of individuals in a population was a major point of observation of Darwin. The individuals vary in their anatomy, physiology and behavior. This variation we now know is caused by genes “circulating” in the population and these genes are “re-mixed” every generation when sperm, eggs and pollen are produced.

Mutations occur in the cells of individuals in the population producing modified genes; this produces more variation. These mutations are random but natural selection certainly is not; it is the “creator” of new subgroups of individuals, races and species.

Because there is competition for survival and reproduction among these variant individuals, those variants with the best body structures, physiology and behaviors will be more efficient during the competition and, most importantly, will produce more and better “fit” offspring. The term “survival of the fittest is now famous. “Fittest” essentially means better adapted to the environment in the sense of the competition just described. Evolution must be thought of a process over time; a very long time.

Genetics was not an organized science at the time of Darwin’s publication and science then knew little of the details of how traits were passed from one generation to another; thus the concepts of chromosomes, genetics, genes, and DNA were unknown. Darwin’s discovery of the broad idea of evolution is therefore all the more to be honored and attributed to his use of the scientific method: expertise at data collection, detailed observation, hypothesis testing and making rational conclusions. 

Darwin called this whole process just described Natural Selection.  It means that subsequent generations will have a higher representation of genetically fit individuals, with the adaptive genes inherited from their parents. Usually this whole process is slow and usually does not cause immediate, radical differences in the appearance of individuals in the population from one generation to another (see below the fact that we occasionally can observe evolution actually occurring over short periods of time)! The differences in structure, function and behavior build up and new species arise. Note that it is the population (or species) that evolves and changes, not the individuals in the “beginning” population. You can imagine that a changing environment, causing more competition, will “speed up” evolution. It is important to note that Natural Selection is not “selecting” populations, but individuals. One can, in one sense, state that natural selection is actually selecting genes — you can read about these ideas elsewhere. We recommend the book by Richard Dawkin’s called “The Selfish Gene.” Dawkins calls the gene the “replicator” (which is replicated and passed on into the next generation) and the individual organism as the “carrier” of the genes where they are expressed. 

As always, for precision in science communication, scientists want precise definitions for words and processes and in this sense, they define evolution as “a change in the gene frequencies in a population.” That simply means what the previous paragraphs stated. Some genes causing better or worse “fitness” become more or less common in the population (their frequencies change). Frequency is simply the percent of a given gene in the population expressed as a percent or decimal. 

It is rather critical to realize that (1) there are always mutations occurring in our genes that we pass on to the next generation, (2) that not all individuals survive to maturity and breed, (3) that individuals do not always mate randomly, they often select particular individuals with certain traits and genes as mates or in the case of plants, pollen and eggs are not combined randomly, (4) that  migration in and out of populations often occurs which would change gene frequencies, (5) that sometimes populations of a species can get so small by accident or isolation that the gene frequency is no longer typical and (6) as Darwin noted, some individuals are naturally selected because of their better fitness and they have more offspring which changes the gene frequencies in the population.

The six points in the previous paragraph would appear to mean that gene frequencies are always changing and thus evolution is always happening.

Humans will see these changes in gene frequencies in the form of preserved parts of organisms in the fossil record. Because fossilization is a rare process, the fossil record is sparse, and we have an occasional “sampling” of evolutionary changes over thousands or millions of years.  Sometimes we may see evolution occurring in “real time.” Many bacteria that infect humans are currently evolving to resist our antibiotics. We can also cause evolution to happen in the laboratory, particularly with microbes. An example of measurable evolution can be seen here.  Killer whales appear to be now splitting into several species “right in front on us.”

Other examples of currently observed evolution are here and also here. Many examples exist but many do not get popularized for the public.

Below is an interesting note on human evolution (is it still happening?)

From Scientific American – September 2014:

Some scientists and science communicators have claimed that humans are no longer subject to natural selection and that human evolution has effectively ceased. In fact, humans have evolved rapidly and remarkably in the past 30,000 years. Straight, black hair, blue eyes and lactose tolerance are all examples of relatively recent traits. Such rapid evolution has been possible for several reasons, including the switch from hunting and gathering to agrarian-based societies, which permitted human populations to grow much larger than before. The more people reproduce within a population, the higher the chance of new advantageous mutations. Humans will undoubtedly continue to evolve into the future. Although it may seem that we are headed toward a cosmopolitan blend of human genes, future generations will likely be striking mosaics of our entire evolutionary past. 

See sixteen of the most common misunderstandings of evolution. You will also find more information here as to how new species arise and many pieces of evidence for evolution.

Evolution is a fact not a belief. Beliefs are often emotions. If you have a belief that has some evidence you may be able to call it a hypothesis, as above. 

One can read and search Darwin’s famous book, “The Origin of Species” on-line here.

 if you have reviewed the ideas of the evolutionary  modern synthesis above, it is an educational learning experience to answer the famous philosophical “puzzle,” “Which Came First, the Chicken or the Egg.” If you have been paying attention, the answer of course cannot be either. But if you ask the question with the nouns made plural, “Which Came First, the Chickens or the Eggs,” the answer is clearly and scientifically, the eggs. For example, during evolution, over many generations, a bird species that was  not the chicken species, produced eggs which were the first generation of the species of bird we call chickens.  These eggs, for the first time ever, contained the gene frequencies of the new chicken species. That would have been a very fine line to notice and cross in the sense of the thousands or millions of years this evolution took to occur, but technically we could might be able to agree on it. This makes the point that evolution takes considerable time and is defined by the “gene frequency” concept, which is not easy to visualize.

Darwin’s Finches and How His Hypothesis Developed into a Fact

The discussion below demonstrates some of the mental history of how Darwin developed his hypothesis of Natural Selection, which became a theory which became the fact of Evolution by Natural Selection.

As a naturalist, Darwin made a trip around the world which was took almost five years; this was on a research vessel, The Beagle, from 1831- to 1836. The vessel traveled, in brief, from England to the Canary Islands, down the eastern coast of South America, to its “tip” and then north up its western coast to the Galapagos Islands and then west to New Zealand, and Australia. Travel continued west to Pacific Islands, Cape Town Africa, back to the east coast of South America and north to the Azores Islands and home.

He made extensive observations and notes and collected numerous specimens of plants, animals, rocks, and fossils whenever the vessel stopped in an island or continental port. He was 22 years old. As an astute observer, naturalist and scientist, his observations had a profound effect on how he viewed the structure and habits of different species of plants and animals. Most persons in the 19th Century thought that species had been individually created by nature or a god, all together at one time and were fixed and unchanging; special creation as it was sometime called.

Eventually he saw patterns that suggested that special creation was extremely unlikely, that species were not “fixed.” He developed the hypothesis that species slowly changed and evolved slowly over time from previous ancestors by the process he called Natural Selection. A hypothesis is a possible scientific explanation for a natural phenomenon — usually the simplest, most logical explanation according to the laws of science.

He spent the next 23 years analyzing his data, gathering new data, reading research papers and communicating with scientists around the world. How, he and other biologists asked, did all the different species of plants and animals evolve to their present-day forms? He published his most famous work, “Origin of Species” in 1859 which outlined his hypothesis in detail.

This book was explosive in terms of cosmic and world views, causing tension in the religious community but excitement in the scientific community. It stimulated many scientists to study Darwin’s, hypothesis and to collect more data for or against it; confirmation of the hypothesis was the trend. With considerable new data, and after several decades, the hypothesis had so much supporting evidence people could now call the hypothesis a theory. A theory is a hypothesis that has been firmly supported with scientific data and may be “on its way” to becoming a fact.

Remember, that at that time, no one knew how traits were coded in the bodies of plants and animals; hence no one spoke of genes or DNA, the genetic material. No one understood where all the variation came from that Darwin saw as the raw material of Natural Selection. Gregor Mendel, “the father of genetics,”  published a brilliant piece of work in 1865, outlining the laws of genetics, but unfortunately it was published in an obscure journal and was not “discovered” until the year 1900. This discovery supported Darwin’s theory and provided greater understanding and certainty of how traits, selected by Natural Selection, were passed from one generation to another. 

As years passed into the 20th Century science discovered details of these genetic processes and filled in the details of Darwin’s main theory. New Sciences and areas of science have developed since 1859 such as Genetics, Gene Expression, Advanced Geology, Bio-geology, Evolution at the Molecular Level, Population Genetics, Cytology, etc. And of course new fossil evidence was constantly being discovered.

Science requires rigorous analysis including mathematics to demonstrate its concepts and to support its theories and laws. In the 1900s, the science of evolution took huge steps in this area with rigorous mathematical work done by three persons famous in that area: William DonaldBillHamiltonRonald A. Fisher and J.B. S. Haldane.

From Wikipedia:

 R. A. Fisher, was an English statistician and biologist who used mathematics to combine Mendelian genetics and natural selection. This helped to create the new Darwinist synthesis of evolution known as the modern evolutionary synthesis. He has been called the greatest biologist since Darwin.

For example, the Fitness and Natural Selection concepts have been been placed into a mathematical context.  Relative fitness  is the survival and/or reproductive rate of a genotype (or phenotype) relative to the maximum survival and/or reproductive rate of other genotypes in the population. (A genotype is the genetic constitution of an individual organism, its specific genes and the phenotype is the actual observable physical/behavioral traits produced by the genes and their interaction with the environment). In the math of evolutionary biology, selection strength becomes a selection coefficient, a measure of the relative strength of selection acting against a genotype. Once we have these concepts placed into precise measurement systems, we can test them in both theoretical and actual experimental situations; we have a more rigorous science.

(See these math fitness and selection concepts explained nicely in a chart and see it used in humans relative to the gene for lactose tolerance in humans. That link discusses the fact that some of us as adults cannot drink milk because we get sick due to our inability to digest the lactose sugar in milk!  However, in a mere 9000 years, some of us evolved a gene allowing lactose digestion!  A fascinating story which is still being investigated.

These mathematical and other new study areas add reams of supporting evidence and understanding of evolution. Today, anyone studying all the details and evidence of the science of evolutionary biology has little doubt that this is the process which produced all the living species on earth. The word “theory” now sounds inadequate for the modern understanding and scientists no longer use it for the process of evolution. For those who have studied all the evidence, the Darwinian concept of Natural Selection placed into the modern evolutionary synthesis framework of evolution is considered a fact. 

If you want to get a more technical look at Natural Selection see this web site but there are many educational books and sites to choose from.

Why do so many people have problems accepting the fact of evolution?

Possibilities could be:

Not enough information getting to the learner: If one has little science background, it can be difficult to absorb much of the evidence and in general understand Natural Selection. Understanding cells, a little chemistry, genetics, DNA, the variation always found in any populations of animals and plants helps immensely with gaining the “big picture” of evolution. Most evolutionary change in a population (change in gene frequency) is abstract, takes long periods of time and is not usually seen in the short human  life span. Although Natural Selection appears easy to put down in words, visualizing it can be difficult. The idea that populations of one species can get geographically  isolated and  slowly change into another species is also difficult to visualize. If one were to be standing and watching this for a million years, one would still have difficulty due to the gradualness of change; there would be difficulty in “drawing a line” between the former species and the new species particularly because a species can have considerable variance in its various populations, races, etc. One cannot see gene flow between populations unless you are measuring it on a regular basis. So common errors of understanding occur; see some of the common misunderstandings about the evolutionary process as noted above. 

Or perhaps Cognitive dissonance?

From Wikipedia: 

In psychology, cognitive dissonance is the mental stress or discomfort experienced by an individual who holds two or more contradictory beliefs, ideas, or values at the same time; performs an action that is contradictory to their beliefs, ideas, or values; or is confronted by new information that conflicts with existing beliefs, ideas or values.

Leon Festinger’s theory of cognitive dissonance focuses on how humans strive for internal consistency. An individual who experiences inconsistency tends to become psychologically uncomfortable, and is motivated to try to reduce this dissonance, as well as actively avoid situations and information likely to increase it.

Cognitive dissonance theory is founded on the assumption that individuals seek consistency between their expectations and their reality. Because of this, people engage in a process called “dissonance reduction” to bring their cognitions and actions in line with one another. This creation of uniformity allows for a lessening of psychological tension and distress. According to Festinger, dissonance reduction can be achieved in four ways.  (1) Change behavior or cognition; (2) Justify behavior or cognition by changing the conflicting cognition; (3) Justify behavior or cognition by adding new cognitions; (4) Ignore or deny any information that conflicts with existing beliefs.

Not accepting scientific concepts in general or having religious views which conflict with evolutionary biology may apply here.

(All remaining pages below are from Wikipedia or other stated sources)

During the survey voyage of HMS Beagle, Darwin was unaware of the significance of the birds of the Galápagos. He had learned how to preserve bird specimens while at the University of Edinburgh and had been keen on shooting, but he had no expertise in ornithology and by this stage of the voyage concentrated mainly on geology.[8] In Galápagos he mostly left bird shooting to his servant Syms Covington.[9] Nonetheless, these birds were to play an important part in the inception of Darwin’s theory of evolution by natural selection.

On the Galápagos Islands and afterward, Darwin thought in terms of “centres of creation” and rejected ideas concerning the transmutation of species.[10] From Henslow’s teaching, he was interested in the geographical distribution of species, particularly links between species on oceanic islands and on nearby continents. On Chatham Island, he recorded that a mockingbird was similar to those he had seen in Chile, and after finding a different one on Charles Island he carefully noted where mockingbirds had been caught.[8] In contrast, he paid little attention to the finches. When examining his specimens on the way to Tahiti, Darwin noted that all of the mockingbirds on Charles Island were of one species, those from Albemarle of another, and those from James and Chatham Islands of a third. As they sailed home about nine months later, this, together with other facts, including what he had heard about Galápagos tortoises, made him wonder about the stability of species.[11][12]

Following his return from the voyage, Darwin presented the finches to the Zoological Society of London on 4 January 1837, along with other mammal and bird specimens that he had collected. The bird specimens, including the finches, were given to John Gould, the famous English ornithologist, for identification. Gould set aside his paying work and at the next meeting, on 10 January, reported that the birds from the Galápagos Islands that Darwin had thought were blackbirds, “gross-beaks” and finches were actually “a series of ground Finches which are so peculiar [as to form] an entirely new group, containing 12 species”. This story made the newspapers.[13][14]

Darwin had been in Cambridge at that time. In early March, he met Gould again and for the first time got a full report on the findings, including the point that his Galápagos “wren” was another closely allied species of finch. The mockingbirds that Darwin had labelled by island were separate species rather than just varieties. Gould found more species than Darwin had expected, [15] and concluded that 25 of the 26 land birds were new and distinct forms, found nowhere else in the world but closely allied to those found on the South American continent.[14]

Darwin now saw that, if the finch species were confined to individual islands, the mockingbirds, this would help to account for the number of species on the islands, and he sought information from others on the expedition. Specimens had also been collected by Captain Robert FitzRoy, FitzRoy’s steward Harry Fuller and Darwin’s servant Covington, who had labelled them by island.[16] From these, Darwin tried to reconstruct the locations from where he had collected his own specimens. The conclusions supported his idea of the transmutation (evolution) of species.[14]


Author Jackie malvin/Wikipedia

Seen above is adapted radiation of finch 1. (Geospiza magnirostris) into three other species of finches found on the Galapagos Islands. Due to the absence of other species of birds, the finches adapted to new niches. The finches beaks and bodies changed allowing them to eat certain types of foods such as nuts, fruits, and insects.

  1. Geospiza magnirostris
  2. Geospiza parvula
  3. Certhidea olivacea
  4. Geospiza fortis


At the time that he rewrote his diary for publication as Journal and Remarks (later The Voyage of the Beagle), he described Gould’s findings on the number of birds, noting that “Although the species are thus peculiar to the archipelago, yet nearly all in their general structure, habits, colour of feathers, and even tone of voice, are strictly American”.[17] In the first edition of The Voyage of the Beagle, Darwin said that “It is very remarkable that a nearly perfect gradation of structure in this one group can be traced in the form of the beak, from one exceeding in dimensions that of the largest gros-beak, to another differing but little from that of a warbler”.[18]

By the time the first edition was published, the development of Darwin’s theory of natural selection was in progress. For the 1845 second edition of The Voyage (now titled Journal of Researches), Darwin added more detail about the beaks of the birds, and two closing sentences which reflected his changed ideas: “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”[19][20]

The remaining land-birds form a most singular group of finches, related to each other in the structure of their beaks, short tails, form of body and plumage: there are thirteen species, which Mr. Gould has divided into four subgroups. All these species are peculiar to this archipelago; and so is the whole group, with the exception of one species of the sub-group Cactornis, lately brought from Bow Island, in the Low Archipelago. Of Cactornis, the two species may be often seen climbing about the flowers of the great cactus-trees; but all the other species of this group of finches, mingled together in flocks, feed on the dry and sterile ground of the lower districts. The males of all, or certainly of the greater number, are jet black; and the females (with perhaps one or two exceptions) are brown. The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in including his sub-group, Certhidea, in the main group) even to that of a warbler. The largest beak in the genus Geospiza is shown in Fig. 1, and the smallest in Fig. 3; but instead of there being only one intermediate species, with a beak of the size shown in Fig. 2, there are no less than six species with insensibly graduated beaks. The beak of the sub-group Certhidea, is shown in Fig. 4. The beak of Cactornis is somewhat  that of a starling, and that of the fourth subgroup, Camarhynchus, is slightly parrot-shaped. Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends. In a  manner it might be fancied that a bird originally a buzzard, had been induced here to undertake the office of the carrion-feeding Polybori of the American continent.[21]

Darwin discussed the divergence of species of birds in the Galápagos more explicitly in his chapter on geographical distribution in On the Origin of Species:

“The most striking and important fact for us in regard to the inhabitants of islands, is their affinity to those of the nearest mainland, without being actually the same species. [In] the Galapagos Archipelago… almost every product of the land and water bears the unmistakable stamp of the American continent. There are twenty-six land birds, and twenty-five of these are ranked by Mr. Gould as distinct species, supposed to have been created here; yet the close affinity of most of these birds to American species in every character, in their habits, gestures, and tones of voice, was manifest…. The naturalist, looking at the inhabitants of these volcanic islands in the Pacific, distant several hundred miles from the continent, yet feels that he is standing on American land. Why should this be so? why should the species which are supposed to have been created in the Galapagos Archipelago, and nowhere else, bear so plain a stamp of affinity to those created in America? There is nothing in the conditions of life, in the geological nature of the islands, in their height or climate, or in the proportions in which the several classes are associated together, which resembles closely the conditions of the South American coast: in fact there is a considerable dissimilarity in all these respects. On the other hand, there is a considerable degree of resemblance in the volcanic nature of the soil, in climate, height, and size of the islands, between the Galapagos and Cape de Verde Archipelagos: but what an entire and absolute difference in their inhabitants! The inhabitants of the Cape de Verde Islands are related to those of Africa,  those of the Galapagos to America. I believe this grand fact can receive no sort of explanation on the ordinary view of independent creation; whereas on the view here maintained, it is obvious that the Galapagos Islands would be likely to receive colonists, whether by occasional means of transport or by formerly continuous land, from America; and the Cape de Verde Islands from Africa; and that such colonists would be liable to modification;— the principle of inheritance still betraying their original birthplace.”[22]


 Quotes from The Origin of Species Quotes (from Goodreads)

The Origin of Species Quotes (showing 1-30 of 120)

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed *into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

― Charles DarwinThe Origin of Species

(*This quote above is from the first edition. Due to angry clerics, he was forced to change this sentence to  “originally breathed by the creator, into a few forms………In this regard, see his letter below (in part) to a friend.


Sunday night

My dear Hooker

Many thanks for Athenæum, received this morning & to be returned tomorrow morning.4 Who would have ever thought of the old stupid Athenæum taking to Oken-like transcendental philosophy written in Owenian style! It will be some time before we see “slime, snot or protolasm” (what an elegant writer) generating a new animal.5 But I have long regretted that I truckled to public opinion & used Pentateuchal term of creation, by which I really meant “appeared” by some wholly unknown process.—6 It is mere rubbish thinking, at present, of origin of life; one might as well think of origin of matter.—

goodnight | C. Darwin

Thwaites has sent me from Ceylon, I suppose through you, two splendid specimens of reciprocally dimorphic plants like Primula. One is Limnanthemum Indicum; & the other Sethia.—10

Above is a Darwin Letter To J. D. Hooker   [29 March 1863]


“One general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die.”
― Charles DarwinThe Origin of Species

“Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult–at least I have found it so–than constantly to bear this conclusion in mind.”
― Charles DarwinThe Origin of Species

“Man selects only for his own good: Nature only for that of the being which she tends.”
― Charles DarwinThe Origin of Species

“I see no good reasons why the views given in this volume should shock the religious views of anyone.”
― Charles DarwinThe Origin of Species

“…for the shield may be as important for victory, as the sword or spear.”
― Charles DarwinThe Origin of Species

“If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.”
― Charles DarwinThe Origin of Species

“There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.”
― Charles DarwinThe Origin of Species

“We will now discuss in a little more detail the Struggle for Existence.”
― Charles DarwinThe Origin of Species

“Nevertheless so profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world, or invent laws on the duration of the forms of life!”
― Charles DarwinThe Origin of Species

“But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is immeasurably superior to man’s feeble efforts, as the works of Nature are to those of Art.”
― Charles DarwinThe Origin of Species

“To conclude, therefore, let no man out of a weak conceit of sobriety, or an ill-applied moderation, think or maintain, that a man can search too far or be too well studied in the book of God’s word, or in the book of God’s works; divinity or philosophy; but rather let men endeavour an endless progress or proficience in both.”—Bacon: “Advancement of Learning”.”
― Charles DarwinOn the Origin of Species

“But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed, be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against the theory. The explanation lies, as I believe, in the extreme imperfection of the geological record.”
― Charles DarwinThe Origin of Species

“I think it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. The forms which stand in closest competition with those undergoing modification and improvement will naturally suffer most.”
― Charles DarwinThe Origin of Species

“As natural selection acts by competition, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates; so that we need feel no surprise at the inhabitants of any one country, although on the ordinary view supposed to have been specially created and adapted for that country, being beaten and supplanted by the naturalised productions from another land.”
― Charles DarwinThe Origin of Species

“When we no longer look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting, I speak from experience, will the study of natural history become!”
― Charles DarwinThe Origin of Species

“A grain in the balance will determine which individual shall live and which shall die – which variety or species shall increase in number, and which shall decrease, or finally become extinct.”
― Charles DarwinThe Origin of Species

“But a plant on the edge of a deserts is said to struggle for life against the drought, though more properly it should be said to be dependent upon the moisture.”
― Charles DarwinThe Origin of Species

“As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.”
― Charles DarwinThe Origin of Species

“But with regard to the material world, we can at least go so far as this— we can perceive that events are brought about not by insulated interpositions of Divine power, exerted in each particular case, but by the establishment of general laws.”—Whewell: “Bridgewater Treatise”.”
― Charles DarwinOn the Origin of Species

“The expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient.”
― Charles DarwinThe Origin of Species

“The only distinct meaning of the word ‘natural’ is STATED, FIXED or SETTLED; since what is natural as much requires and presupposes an intelligent agent to render it so, i.e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once.”—Butler: “Analogy of Revealed Religion”.”
― Charles DarwinOn the Origin of Species

“Look at a plant in the midst of its range! Why does it not double or quadruple its numbers? We know that it can perfectly well withstand a little more heat or cold, dampness or dryness, for elsewhere it ranges into slightly hotter or colder, damper or drier districts. In this case we can clearly see that if we wish in imagination to give the plant the power of increasing in numbers, we should have to give it some advantage”
― Charles DarwinOn the Origin of Species

“When we compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature. And if we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, we are driven to conclude that this great variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent species had been exposed under nature. There is, also, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation; and that, when the organisation has once begun to vary, it generally continues varying for many generations. No case is on record of a variable organism ceasing to vary under cultivation. Our oldest cultivated plants, such as wheat, still yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.”
― Charles DarwinOn the Origin of Species

“I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that natural selection has been the most important, but not the exclusive, means of modification.”
― Charles DarwinOn the Origin of Species

“I will here give a brief sketch of the progress of opinion on the Origin of Species. Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created. This view has been ably maintained by many authors. Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre existing forms. Passing over allusions to the subject in the classical writers (Aristotle, in his “Physicae Auscultationes” (lib.2, cap.8, s.2), after remarking that rain does not fall in order to make the corn grow, any more than it falls to spoil the farmer’s corn when threshed out of doors, applies the same argument to organisation; and adds (as translated by Mr. Clair Grece, who first pointed out the passage to me), “So what hinders the different parts (of the body) from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident. And in  manner as to other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened  as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity; and whatsoever things were not thus constituted, perished and still perish.” We here see the principle of natural selection shadowed forth, but how little Aristotle fully comprehended the principle, is shown by his remarks on the formation of the teeth.), the first author who in modern times has treated it in a scientific spirit was Buffon. But as his opinions fluctuated greatly at different periods, and as he does not enter on the causes or means of the transformation of species, I need not here enter on details.”
― Charles DarwinThe Origin of Species

“Youatt gives an excellent illustration of the effects of a course of selection which may be considered as unconscious, in so far that the breeders could never have expected, or even wished, to produce the result which ensued—namely, the production of the distinct strains. The two flocks of Leicester sheep kept by Mr. Buckley and Mr. Burgess, as Mr. Youatt remarks, “Have been purely bred from the original stock of Mr. Bakewell for upwards of fifty years. There is not a suspicion existing in the mind of any one at all acquainted with the subject that the owner of either of them has deviated in any one instance from the pure blood of Mr. Bakewell’s flock, and yet the difference between the sheep possessed by these two gentlemen is so great that they have the appearance of being quite different varieties.”
― Charles DarwinOn the Origin of Species

Darwin’s loss of faith – from Wikipedia


An 1868 photo of by Julia Margaret Cameron.

In his later private autobiography, Darwin wrote of the period from October 1836 to January 1839: 

“During these two years I was led to think much about religion. Whilst on board the Beagle I was quite orthodox, & I remember being heartily laughed at by several of the officers (though themselves orthodox) for quoting the Bible as an unanswerable authority on some point of morality. I suppose it was the novelty of the argument that amused them. But I had gradually come, by this time, to see that the Old Testament from its manifestly false history of the world, with the Tower of Babelrainbow as a sign, etc., etc., and from its attributing to God the feelings of a revengeful tyrant, was no more to be trusted than the sacred books of the Hindoos, or the beliefs of any barbarian.”[41]

In seeking to explain his observations, by early 1837 Darwin was speculating in his notebooks on transmutation of species and writing of “my theory”. His journal for 1838 records “All September read a good deal on many subject: thought much upon religion. Beginning of October ditto.” At this time he outlined ideas of comparative anthropology, from his knowledge of different religious beliefs around the world as well as at various times in history, and came to the view that scriptures were unreliable and contradictory.[42

Early in 1842, Darwin wrote about his ideas to Lyell, who noted that his ally “denies seeing a beginning to each crop of species”.[50] On 11 January 1844 Darwin mentioned his theorising to the botanist Joseph Dalton Hooker, writing with melodramatic humour “I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable. Heaven forfend me from Lamarck nonsense of a ‘tendency to progression’ ‘adaptations from the slow willing of animals’ &c,—but the conclusions I am led to are not widely different from his—though the means of change are wholly so—I think I have found out (here’s presumption!) the simple way by which species become exquisitely adapted to various ends.”[51][52] Hooker replied “There may in my opinion have been a series of productions on different spots, & also a gradual change of species. I shall be delighted to hear how you think that this change may have taken place, as no presently conceived opinions satisfy me on the subject.”[53]

From around 1849 Darwin stopped attending church, but Emma and the children continued to attend services.[14] On Sundays Darwin sometimes went with them as far as the lych gate to the churchyard, and then he would go for a walk. During the service, Emma continued to face forward when the congregation turned to face the altar for the Creed, sticking to her Unitarian faith.

Darwin had already wondered about the materialism implied by his ideas, noting in his transmutation notebook “Thought (or desires more properly) being hereditary it is difficult to imagine it anything but structure of brain hereditary, analogy points out to this. – love of the deity effect of organization, oh you materialist!”[44]

Darwin was interested in ideas of Natural “laws of harmony”, and made enquiries into animal breeding. Having read the new 6th edition of the Revd. Thomas Malthus‘s Essay on the Principle of Population, around late November 1838 he compared breeders selecting traits to a Malthusian Nature selecting from variants thrown up by chance so that “every part of newly acquired structure is fully practical & perfected”,[48] thinking this “a beautiful part of my theory”.[49] The theodicy of Paley and Thomas Malthus vindicated evils such as starvation as a result of a benevolent creator’s laws which had an overall good effect. To Darwin, Natural selection produced the good of adaptation but removed the need for design,[8] and he could not see the work of an omnipotent deity in all the pain and suffering such as the ichneumon wasp paralysing caterpillars as live food for its eggs.[9]

 For the second edition, Darwin added these lines to the last chapter, with attribution to “a celebrated author and divine”. [58][59]

Autobiography on gradually increasing disbelief

In his autobiography written in 1876 Darwin reviewed questions about Christianity in relation to other religions and how “the more we know of the fixed laws of nature the more incredible do miracles become”. Though “very unwilling to give up my belief”, he found that “disbelief crept over me at a very slow rate, but was at last complete. The rate was so slow that I felt no distress, and have never since doubted even for a single second that my conclusion was correct.” He noted how “The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection has been discovered”, and how Paley’s teleological argument had difficulties with the problem of evil.[62]

Even when writing On the Origin of Species in the 1850s he was still inclined to theism, but his views gradually changed to agnosticism:

Another source of conviction in the existence of God, connected with the reason and not with the feelings, impresses me as having much more weight. This follows from the extreme difficulty or rather impossibility of conceiving this immense and wonderful universe, including man with his capacity of looking far backwards and far into futurity, as the result of blind chance or necessity. When thus reflecting I feel compelled to look to a First Cause having an intelligent mind in some degree analogous to that of man; and I deserve to be called a Theist.

This conclusion was strong in my mind about the time, as far as I can remember, when I wrote the Origin of Species; and it is since that time that it has very gradually with many fluctuations become weaker. But then arises the doubt–can the mind of man, which has, as I fully believe, been developed from a mind as low as that possessed by the lowest animal, be trusted when it draws such grand conclusions? May not these be the result of the connection between cause and effect which strikes us as a necessary one, but probably depends merely on inherited experience? Nor must we overlook the probability of the constant inculcation in a belief in God on the minds of children producing so strong and perhaps an inherited effect on their brains not yet fully developed, that it would be as difficult for them to throw off their belief in God, as for a monkey to throw off its instinctive fear and hatred of a snake.

I cannot pretend to throw the least light on such abstruse problems. The mystery of the beginning of all things is insoluble by us; and I for one must be content to remain an Agnostic.[63]

In his 1871 book The Descent of Man Darwin clearly saw religion and “moral qualities” as being important evolved human social characteristics. Darwin’s frequent pairing of “Belief in God” and religion with topics on superstitions and fetishism throughout the book can also be interpreted as indicating how much truth he assigned to the former.

In the introduction Darwin wrote:

“Ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.”[70]

Later on in the book he dismisses an argument for religion being innate:

“Belief in God — Religion. — There is no evidence that man was aboriginally endowed with the ennobling belief in the existence of an Omnipotent God. On the contrary there is ample evidence, derived not from hasty travellers, but from men who have long resided with savages, that numerous races have existed, and still exist, who have no idea of one or more gods, and who have no words in their languages to express such an idea. The question is of course wholly distinct from that higher one, whether there exists a Creator and Ruler of the universe; and this has been answered in the affirmative by some of the highest intellects that have ever existed.”[71]

“The belief in God has often been advanced as not only the greatest, but the most complete of all the distinctions between man and the lower animals. It is however impossible, as we have seen, to maintain that this belief is innate or instinctive in man. On the other hand a belief in all-pervading spiritual agencies seems to be universal; and apparently follows from a considerable advance in man’s reason, and from a still greater advance in his faculties of imagination, curiosity and wonder. I am aware that the assumed instinctive belief in God has been used by many persons as an argument for His existence. But this is a rash argument, as we should thus be compelled to believe in the existence of many cruel and malignant spirits, only a little more powerful than man; for the belief in them is far more general than in a beneficent Deity. The idea of a universal and beneficent Creator does not seem to arise in the mind of man, until he has been elevated by long-continued culture.”[72]

Enquiries about religious views

Fame and honours brought a stream of enquiries about Darwin’s religious views, leading him to comment “Half the fools throughout Europe write to ask me the stupidest questions.”[73]He sometimes retorted sharply, “I am sorry to have to inform you that I do not believe in the Bible as a divine revelation, & therefore not in Jesus Christ as the Son of God”,[74] and at other times was more guarded, telling a young count studying with Ernst Haeckel that “Science has nothing to do with Christ; except in so far as the habit of scientific research makes a man cautious in admitting evidence. For myself I do not believe that there ever has been any Revelation. As for a future life, every man must judge for himself between conflicting vague probabilities.”[75] He declined a request by the Archbishop of Canterbury to join a ‘Private Conference’ of devout scientists to harmonise science and religion, for he saw “no prospect of any benefit arising” from it.[76]

Caution about publication, spiritualism

In 1873 Darwin’s son George wrote an essay which boldly dismissed prayer, divine morals and “future rewards & punishments”. Darwin wrote “I would urge you not to publish it for some months, at the soonest, & then consider whether you think it new & important enough to counterbalance the evils; remembering the cart-loads which have been published on this subject. – The evils on giving pain to others, & injuring your own power & usefulness… It is an old doctrine of mine that it is of foremost importance for a young author to publish.. only what is very good & new… remember that an enemy might ask who is this man… that he should give to the world his opinions on the deepest subjects?… but my advice is to pause, pause, pause.”[80]

During the public interest in Modern Spiritualism, Darwin attended a séance at Erasmus‘s house in January 1874, but as the room grew stuffy Darwin went upstairs to lie down, missing the show, with sparks, sounds and the table rising above their heads. While Galton thought it a “good séance”, Darwin later wrote “The Lord have mercy on us all, if we have to believe such rubbish”[81] and told Emma that it was “all imposture” and “it would take an enormous weight of evidence” to convince him otherwise. At a second séance Huxley and George found that Williams was nothing but a cheat, to Darwin’s relief.

In 1876 Darwin wrote the following regarding his publicly stated position of agnosticism: “Formerly I was led… to the firm conviction of the existence of God and the immortality of the soul. In my Journal I wrote that whilst standing in the midst of the grandeur of a Brazilian forest, ‘it is not possible to give an adequate idea of the higher feelings of wonder, admiration, and devotion, which fill and elevate the mind.’ I well remember my conviction that there is more in man than the mere breath of his body. But now the grandest scenes would not cause any such convictions and feelings to rise in my mind.”[82]

In November 1878 when George Romanes presented his new book refuting theism, A Candid Examination of Theism by “Physicus”, Darwin read it with “very great interest”, but found it unconvincing; the arguments it put forward left open the possibility that God had initially created matter and energy with the potential of evolving to become organised.[83][84]


In 1879 John Fordyce wrote asking if Darwin believed in God, and if theism and evolution were compatible. Darwin replied that a man “can be an ardent Theist and an evolutionist”, citing Charles Kingsley and Asa Gray as examples, and for himself, “In my most extreme fluctuations I have never been an atheist in the sense of denying the existence of a God.— I think that generally (& more and more so as I grow older) but not always, that an agnostic would be the most correct description of my state of mind.”[85]

Those opposing religion often took Darwin as their inspiration and expected his support for their cause, a role he firmly refused. In 1880 there was a huge controversy when the atheist Charles Bradlaugh was elected as a member of parliament and then prevented from taking his seat in the House of Commons. In response, the secularist Edward Aveling toured the country leading protests.[86] In October of that year Aveling wanted to dedicate his book on Darwin and his Works to Darwin and asked him for permission. Darwin declined, writing that “though I am a strong advocate for free thought on all subjects, yet it appears to me (whether rightly or wrongly) that direct arguments against Christianity & theism produce hardly any effect on the public; & freedom of thought is best promoted by the gradual illumination of men’s minds, which follows from the advance of science. It has, therefore, been always my object to avoid writing on religion, & I have confined myself to science. I may, however, have been unduly biased by the pain which it would give some members of my family, if I aided in any way direct attacks on religion.”[87]

Aveling and Büchner

In Germany militant Darwinismus elevated Darwin to heroic status. When the eminent Freethinker Doctor Ludwig Büchner requested an audience he thought he was greeting a noble ally. To Darwin this was a grotesque misunderstanding, but he felt unable to refuse. Darwin’s wife Emma Darwin expressed her expectation that their guest “will refrain from airing his very strong religious opinions” and invited their old friend the Revd. John Brodie Innes. On Thursday 28 September 1881 Büchner arrived with Edward Aveling. Darwin’s son Frank was also present. Darwin wittily explained that “[Brodie] & I have been fast friends for 30 years. We never thoroughly agreed on any subject but once and then we looked at each other and thought one of us must be very ill”.[88]

In uncharacteristically bold discussions after dinner Darwin asked his guests “Why do you call yourselves Atheists?” When they responded that they “did not commit the folly of god-denial, [and] avoided with equal care the folly of god-assertion”, Darwin gave a thoughtful response, concluding that “I am with you in thought, but I should prefer the word Agnostic to the word Atheist.” Aveling replied that, “after all, ‘Agnostic’ was but ‘Atheist’ writ respectable, and ‘Atheist’ was only ‘Agnostic’ writ aggressive.” Darwin smiled and responded “Why should you be so aggressive? Is anything gained by trying to force these new ideas upon the mass of mankind? It is all very well for educated, cultured, thoughtful people; but are the masses yet ripe for it?” Aveling and Büchner questioned what would have happened if Darwin had been given that advice before publication of the Origin, and had confined “the revolutionary truths of Natural and Sexual Selection to the judicious few”, where would the world be? Many feared danger if new ideas were “proclaimed abroad on the house-tops, and discussed in market-place and home. But he, happily for humanity, had by the gentle, irresistible power of reason, forced his new ideas upon the mass of the people. And the masses had been found ripe for it. Had he kept silence, the tremendous strides taken by human thought during the last twenty-one years would have been shorn of their fair proportions, perhaps had hardly been made at all. His own illustrious example was encouragement, was for a command to every thinker to make known to all his fellows that which he believed to be the truth.”[88][89]

Their talk turned to religion, and Darwin said “I never gave up Christianity until I was forty years of age.” He agreed that Christianity was “not supported by the evidence”, but he had reached this conclusion only slowly. Aveling recorded this discussion, and published it in 1883 as a penny pamphlet.[88][89]Francis Darwin thought it gave “quite fairly his impressions of my father’s views, but took issue with any suggestion of similar religious views, saying “My father’s replies implied his preference for the unaggressive attitude of an Agnostic. Dr. Aveling seems to regard the absence of aggressiveness in my father’s views as distinguishing them in an unessential manner from his own. But, in my judgment, it is precisely differences of this kind which distinguish him so completely from the class of thinkers to which Dr. Aveling belongs.”[90]


Darwin’s Westminster Abbey funeral expressed a public feeling of national pride, and religious writers of all persuasions praised his “noble character and his ardent pursuit of truth”, calling him a “true Christian gentleman”. In particular the Unitarians and free religionists, proud of his Dissenting upbringing, supported his naturalistic views. The Unitarian William Carpenter carried a resolution praising Darwin’s unravelling of “the immutable laws of the Divine Government”, shedding light on “the progress of humanity”, and the Unitarian preacher John White Chadwick from New York wrote that “The nation’s grandest temple of religion opened its gates and lifted up its everlasting doors and bade the King of Science come in.”

Posthumous Autobiography

Darwin decided to leave a posthumous memoir for his family, and on Sunday 28 May 1876 he began Recollections of the Development of my mind and character. He found this candid private memoir easy going, covering his childhood, university, life on the Beagle expedition and developing work in science. A section headed “Religious Belief” opened just before his marriage, and frankly discussed his long disagreement with Emma. At first he had been unwilling to give up his faith, and had tried to “invent evidence” supporting the Gospels, but just as his clerical career had died a slow “natural death”, so too did his belief in “Christianity as a divine revelation”. “Inward convictions and feelings” had arisen from natural selection, as had survival instincts, and could not be relied on. He was quick to show Emma’s side of the story and pay tribute to “your mother, … so infinitely my superior in every moral quality … my wise adviser and cheerful comforter”.[91]

The Autobiography of Charles Darwin was published posthumously, and quotes about Christianity were omitted by Darwin’s wife Emma and his son Francis because they were deemed dangerous for Charles Darwin’s reputation. Only in 1958 did Darwin’s granddaughter Nora Barlow publish a revised version which contained the omissions.[92] This included statements discussed above in Autobiography on gradually increasing disbelief, and others such as the following:

“By further reflecting that the clearest evidence would be requisite to make any sane man believe in the miracles by which Christianity is supported, — that the more we know of the fixed laws of nature the more incredible, do miracles become, — that the men at that time were ignorant and credulous to a degree almost incomprehensible by us, — that the Gospels cannot be proved to have been written simultaneously with the events, – that they differ in many important details, far too important as it seemed to me to be admitted as the usual inaccuracies of eyewitness; – by such reflections as these, which I give not as having the least novelty or value, but as they influenced me, I gradually came to disbelieve in Christianity as a divine revelation. The fact that many false religions have spread over large portions of the earth like wild-fire had some weight with me. Beautiful as is the morality of the New Testament, it can hardly be denied that its perfection depends in part on the interpretation which we now put on metaphors and allegories.” (p.86)

“I can indeed hardly see how anyone ought to wish Christianity to be true; for if so the plain language of the text seems to show that the men who do not believe, and this would include my Father, Brother and almost all my best friends, will be everlastingly punished. And this is a damnable doctrine.” (p. 87)

“The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection had been discovered. We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man. There seems to be no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows. Everything in nature is the result of fixed laws.” (p.87)

“At the present day (ca. 1872) the most usual argument for the existence of an intelligent God is drawn from the deep inward conviction and feelings which are experienced by most persons. But it cannot be doubted that HindoosMahomadans and others might argue in the same manner and with equal force in favor of the existence of one God, or of many Gods, or as with the Buddhists of no God…This argument would be a valid one if all men of all races had the same inward conviction of the existence of one God: but we know that this is very far from being the case. Therefore I cannot see that such inward convictions and feelings are of any weight as evidence of what really exists.” (p.91)