What did Charles Darwin do?

The living


background information

Charles Darwin. Detail from a painting by George Richmond, late 1830s.
From wikipedia, Charles Darwin (public domain).

Until the 19th century, the biblical story of creation dominated the idea of ​​the origin of life in Christian culture. With the Copernican Revolution (more) it became clear to many people that one cannot take all statements of the Bible literally. In the 17th and 18th centuries, occupation “with stones” had also become very fashionable - geology was to emerge from it. Geologists began to classify rocks according to the time they were deposited. They realized that the earth must have been so much older than the literal interpretation of the Bible suggested. They could only guess at the real age; the former “child prodigy” Lord Kelvin (who attended university at the age of 10) estimated the earth to be 98 million years old in 1862 - an estimate that he revised downwards several times up to 1897, to a maximum of 24 million years . He thought that a celestial body like the sun could not shine any longer without using up all of its fuel (a problem that was only solved with the discovery of nuclear fusion as an energy source). Another assessment was fueled by the discovery of fossilized, extinct animal species: soon the geologists recognized that certain fossils only appeared in rocks of a certain age and were therefore suitable for age determination. The discoveries also shook belief in the immutability of creation and raised uncomfortable questions about Providence: Why did God first create species that he later destroyed?

In 1809 the French biologist Jean-Baptiste de Lamarck, professor at the Paris Museum of Natural History, published his “Philosophy zoologique”For the first time a theory of evolution: Just as adult animals develop from a fertilized egg cell through gradual changes, the world of living things should develop from the simplest to increasingly complex forms of life. He had recognized the variability of the species in fossil molluscs from the Paris basin. Although his idea found supporters among naturalists at the time, it hardly aroused any reaction from the general public. That should be very different in 1859 than Charles Darwin's book "The Origin of Species" appeared. Darwin had recognized that evolution included not only the change in species from an original to a derived state, already recognized by Lamarck (now called "anagenesis" by biologists), but also the splitting of old species into new ones - evolution through branching (from Darwin figuratively described as the “tree of life”, now called “cladogenesis” by biologists). The species had then developed from common ancestors, in Lamarck's imagination each line of descent had arisen from an infusorium created by "spontaneous generation".

Darwin's theory was based on two findings: First, he knew that all individuals of a species are different from one another and that these differences are hereditary. They are the basis of animal and plant breeding (Darwin was a member of two pigeon breeding associations), where the best specimens from the breeder's point of view are used for further breeding and the selected characteristics are increasingly pronounced. Second, an excess of offspring is produced in nature; The British economist Thomas Malthus had already described this in his “Essay on the Principle of Population” in 1798 and predicted famine. However, the surplus of offspring usually does not lead to an increase in the number of living beings, rather it remains the same on average. So only a part of the offspring survives; and whoever survived was, according to Darwin, not purely by chance: rather, they took over selective forces of nature like food supply or predators, the role of the breeder - the selection of the best specimens. In nature, these are the individuals who are best adapted to the conditions of their environment, for example found more food or were more difficult to recognize for predators. These are more likely to reproduce. These "natural selection”Takes place indirectly and unconsciously; In the course of time, however, species that are better adapted to their environment emerge. So it is not the species that adapt to the environment (Lamarck's idea), but the environmental conditions ensure that some individuals can reproduce more than others and so their characteristics can spread further.

The momentous journey of a naturalist around the world

As a young man, Charles Darwin had studied the natural sciences intensively at the Universities of Edinburgh and Cambridge, and a lifelong love of geological research developed there. At the age of 22, in December 1831, he began a five-year activity as a naturalist on the H.M.S. Beagle. The Beagle was supposed to map the southern coast of South America and sail around the world to keep chronometric records to determine longitude. On this trip Darwin examined the geology, fauna and flora of South America in particular, including the fauna of the Galapagos archipelago, which later became so famous. (Darwin did not notice the later so important biodiversity on the islands at first.) This trip should be significant for the development of the evolution theory for two reasons: Firstly, Darwin read Lyell's “Principles of Geology” (more) on the ship, in which Lyell shows that small changes can add up to huge changes over very long periods of time. On the other hand, hardly any natural scientist had gotten to know the entire world of nature so intensively as Darwin, who carefully observed and thoughtfully processed the habitats, behavior and distribution areas of animals and plants. When Darwin began to work out his theories, generations of science historians were concerned; There is still no agreement today.

Darwin himself refers in “The Origin of Species” to the distribution of the inhabitants of South America and the “relationships between the present and the earlier population of this part of the world”; Facts that seemed to him “to shed some light on the origin of species”. In September 1832, for example, while the Beagle was staying in Bahía Blanca, he found the bones of an extinct giant sloth that was anatomically similar to the living sloth, but was almost the size of an elephant - much too big to live on trees. On the Rio Negro in Patagonia, he heard gauchos speak of a “small ostrich”, which should appear next to the common “South American ostrich” (today the ratites that live in South America are called rheas) - Darwin soon realized that the range of the two species hardly overlapped . Extinct relatives of today's animals and similar but separate species - time and space, Darwin soon suspected, could somehow give rise to new animal species.

Upon his return in October 1836, Darwin began to process the extensive material he had collected during the trip. He gave a five-part “Zoology of the Journey of the H.M.S. Beagle ”, published his diary (“ Die Fahrt der Beagle ”) - and thought further about whether species can arise through gradual changes. The animals collected on the trip had been examined by specialists - Richard Owen examined the fossil mammals, John Gould the birds, Thomas Bell the reptiles. The bird life of the Galapagos Islands played a decisive role in this. Gould recognized that the islands each had their own species of mockingbirds and earth finches - and Darwin recognized the importance of this discovery: the Galapagos Islands, which are actually the peaks of volcanic mountains hidden in the sea, were never connected to the mainland; all life had therefore immigrated from the mainland. In all of South America there is only one species of mockingbird, and three species on three islands in the Galapagos. Couldn't the mainland species have reached the islands and the three species developed from it on the respective islands? Wouldn't that be a fine example of the mutability of species? The finches also gave an idea of ​​how the “selective forces of nature” might have played their role in this species formation: The beaks of the three species were each adapted to different food - insects, cacti or seeds. Darwin should take this thought further: Why shouldn't all species have a common ancestor as well? So he developed the idea of ​​the "tree of life", which branches out from a common trunk and finally brings about the diversity of life.


The "tree of Life”, From notebook B from 1837. Fig. From wikipedia.

Darwin initially recorded such thoughts in secret notebooks that were only found after his death. Over seven years - from 1837 to 1844 - he worked out a treatise on evolution that was ready to be printed, but which he never published. Only to a friend, the botanist Joseph Hooker, did he hint at what he was thinking about. In 1844 an anonymous author published the “Natural History of the Creation of the Universe, the Earth and the Organisms on it”, which also represented evolution. This book sparked a public discussion about evolution, had enthusiastic supporters and staunch opponents. The book was a shock to Darwin, as the author had grasped the basic idea of ​​evolution correctly - albeit on a weak factual basis. Darwin began working on a better factual basis for his own work, which included a pigeon breeding program and eight years of intensive research into barnacles (a group of crabs that includes barnacles and barnacles, among others). In 1856 he presented his ideas for the first time in the circle of friends (including in conversations with Hooker and Charles Lyell) for discussion, and on Lyell's advice began to write a book. Then in 1858 he received a letter from the naturalist Alfred Russel Wallace with a manuscript containing a theory of the origin of species that corresponded exactly to that of Darwin.

The other Darwin

Alfred Russel Wallace had mostly taught himself his knowledge of nature; as the eighth of nine children of an impoverished lawyer, a university degree was out of the question for him. In 1848, at the age of 25, inspired by the travel reports of Alexander von Humboldt and Charles Darwin, he went to Brazil to collect animals and plants that he wanted to sell to museums. He stayed in the Amazon for four years - and lost his collection in a shipwreck on the return voyage. Only the fact that his agent Samuel Stevens had insured the cargo without his knowledge saved him from financial ruin. In 1854 he set out again, this time for eight years on the islands of the Malay Archipelago. He collected many thousands of animals that he sent to Stevens - and quickly discovered the variability within the species. Wallace also examined the distribution patterns of many animal species in “his” archipelago, and related them to their origins. When he combined these thoughts with Malthus ’study on population growth, he came to the same conclusion as Darwin - whose reasoning he did not know, although he had corresponded with him for two years. So it came about that he sent Darwin his manuscript ... The rest is history: Joseph Hooker and Charles Lyell put two items on the agenda on the eve of the annual meeting of the Linnaeus Society: Darwin's 1844 treatise and Wallace's manuscript. This proved Darwin's earlier authorship. Although Darwin later paid tribute to Wallace in his "Origin of Species", he was almost second to be forgotten. But there are still those Wallace line, a biogeographical dividing line running through the middle of the Malay Archipelago, separating an Asian flora and fauna in the west from an Australian counterpart in the east. Wallace described it in his book “The Malay Archipelago” in 1869, and it is named after him today.

Wallace himself always recognized Darwin's lead in developing a theory of the origin of species; he called his own 1889 book on natural selection “Darwinism”. Today, however, Wallace is assigned a completely different pioneering role: from an early age he was concerned with the global interrelationships of life on earth. He dealt with the role of dust in the atmosphere in cloud formation and thus its influence on the earth's climate. Darwin had also caught dust on the Beagle and suspected that it came from the Sahara and was flying to South America. Darwin was only interested in the spread of spores and small organisms with this dust; Wallace, on the other hand, anticipated the approach of modern earth system science.

Within a year and a half after this shock, Darwin completed his book The Origin of Species. Darwin's book benefited from his profound knowledge of nature - it overflows with examples from all branches of natural history. (Wallace is said to have read the book Darwin had sent him five or six times, and each time he was even more impressed.) The masses of material could not prevent a discussion: the idea of ​​a changing flora and fauna was too strange; and furthermore, according to Darwin, organisms were the result of a natural process, and not the creation of a divine Master. Darwin or the Bible? The discussion is not quite over to this day (here), and because the book represented such a radical break with traditional worlds of thought, it is considered the “foundation stone of the modern world” (the historian of science Janet Browne, see Literature Tips.

Darwin's "Origin of Species" changes the world

With his theory of evolution, Darwin provided a solution to an old problem for naturalists: they had noticed that many animal groups had common characteristics. For example, frogs, snakes, birds and humans have a spine.Obviously, some animals were so similar that one spoke of "relationships": For example, cats are evidently related to lynxes, lions and cheetahs, and the ancient naturalists put them in a common group (the "feline"). It follows from Darwin's theory that frogs, snakes, birds and mammals all descend from a common ancestor to whom they all owe their spine. Cats, lynxes, lions and cheetahs are actually related through a common ancestor - and not just coincidentally similar. Darwin's theory stimulated the zoologists to conduct comparative investigations in which they discovered numerous “homologies”: structures with a common ancestral origin. The word homology was coined by the British anatomist Richard Owen, who noticed that the limbs of the most varied of living beings had a similar structure: for example, the bones in the wings of birds are composed exactly like in our arms. Owen believed, however, that this likeness was the Creator's plan; Darwin's explanation was that common history of origin. The study of the development of embryos provided further evidence: In the 1830s, the German-Baltic naturalist Karl Ernst von Baer discovered that embryos have a shape common to all animal species in their early phase (and that all organs can be traced back to three layers in the embryo , which he called cotyledons), the species-specific properties arise later. Ernst Haeckel later shows that they are recapitulating the phylogenetic development: the vertebrate embryos go through a stage in which they have gills. (This finding, which Haeckel declared to be the “biogenetic law”, is now only referred to as a “basic rule”, as there are exceptions - embryos also have their own adaptations to their environment, which can lead to deviations.) This sequence shows that in the Evolution always build new features on existing features. These findings led to the fact that some aspects of Darwin's theory, such as the idea of ​​evolution as such and of common ancestry, had already prevailed a few years after the publication of "The Origin of Species".

Other aspects sparked heated discussions, such as the theory of the natural selection as the cause of evolution and Darwin's ideas about the origin of species. Not only the literal interpretation of the Bible played a role, but also scientific theories such as the "theory of types" - the belief that goes back to the Greeks that all apparently changeable natural phenomena can be divided into unchangeable classes ("types"). For Aristotle, a chicken was just a (more or less flawed) expression of a "chicken ness"; Darwin, however, made the individual characteristics of the individual individuals within the classes the starting point of natural selection - a knowledge that he shared with Alfred Russel Wallace, but which was not to be generally recognized until 80 years later. Today this way of thinking is the basis of population thinking in biology: A species is the totality of its populations, with all the individual diversity contained in them. In the Soviet Union and by many of its supporters, Darwinism was rejected for another reason: it was considered a capitalist ideology because of social Darwinism.

Social darwinism

While Darwin's ideas were hotly contested in biology in the 19th century, they were soon used to justify economic inequality in Victorian England. The English philosopher Herbert Spencer was the first to apply the theory of evolution to society and, in 1864, coined the term “survival of the fittest”; a term that Darwin adopted in 1869 in the 5th edition of his Origin of Species. Spencer believed that the “invisible hand of evolution” ensures that what is best for the long-term existence of society prevails in society as well. In the wild capitalism of early industrialization (more) this was understood to mean that the “struggle” should also be the decisive driving force in economic and social policy and thus the elbow society of Manchester capitalism was justified.

The English naturalist Francis Galton (like Darwin a grandson of Erasmus Darwin) proposed a program for breeding optimized humans, which he later called "eugenics". Others, such as the Krakow-based sociologist Ludwig Gumplowicz, transferred the idea to an alleged struggle of the “races” for survival; this justified the annihilation of indigenous peoples under imperialism. Under the name “Rassenhygiene” it came to the “destruction of unworthy life” in Nazi Germany. These perversions had nothing to do with the original ideas of Darwin and Spencer - Spencer, as a liberal, rejected state interference in society; Darwin's natural selection concerned the individuals within a population, not any “races” (1) (and there is no body consciously allowed to decide on “inferiority” - a role which in the case of racial hygiene the killers themselves always assumed).

But Darwin, too, as his sometimes very negative descriptions of the indigenous peoples he met on his journey show, overlooked a crucial point: the importance of cultural evolution in people and societies. For Darwin, his English society was the measure of all things; he did not see the life of indigenous peoples as an adaptation to their very own circumstances. He did not recognize the Tierra del Fuego, described by Darwin as "the most wretched and wretched creatures I had ever seen", as a people who have survived for thousands of years without technical aids in an extremely inhospitable climate and can build boats from branches and bark, from which it hunted fish and seals with spears - and which had a complex language and a complex spiritual life. Above all, he wasn't even surprised when kidnapped children on the Beagle quickly learn the English language and manners: How big can the biological difference be when children learn a completely different life so quickly? It is quite insignificant - cultural evolution in humans has long since replaced the meaning of biological evolution. The fact that we live very differently today than the farmers did 300 years ago has nothing to do with biological evolution, but everything to do with cultural evolution. However, this is not Darwinian - on the contrary, cultural evolution consists in the passing on of acquired knowledge and skills. Sociobiologists point out that cultural evolution also has biological (and thus subject to evolution and understandable with its help) foundations; evolution may therefore help explain cultural developments. But Darwinist ideas are completely unsuitable for wanting to control non-Darwinist social developments. The fact that it was tried nevertheless is not to blame Darwin, but to those who did it.

More about cultural evolution.

The synthesis of genetics and the theory of evolution

Genetics, which emerged at the end of the 19th century, initially strengthened the skeptical camp: many geneticists believed that mutations were sufficient to explain the formation of new species. It was not until the 1930s and 1940s that the results of genetics and the theory of evolution were brought together; The publication “The genetic foundations of speciation” by the Ukrainian-American naturalist and geneticist was particularly important Theodosius Dobzhansky. As a naturalist, he had studied beetles in his youth and studied the theory of evolution; at the age of 27 he emigrated to the USA and worked in the “fly laboratory” of Thomas Hunt Morgan (more), where he got to know genetics. His work laid the foundation for the synthesis of genetics and evolutionary theory by the German-American evolutionary biologist Ernst Mayr was pushed further. Dobzhansky and Mayr showed that the mutations discovered by geneticists are a major cause of the variability of individuals within a species, and that this is the starting point for Darwin's natural selection. The biologist and writer Julian Huxley presented the results to a wide audience with his book “Evolution: The Modern Synthesis”. Since then, Darwinism, expanded to include genetic explanations, in the form of the “synthetic theory of evolution” has been the basic structure of evolutionary thinking in biology.

Is evolution "just" a theory?

While in everyday use the word theory often only refers to an assumption, natural science understands a theory to be a picture of reality that can be checked as closely as possible. If, as in the case of evolution, thousands of facts support the theory, but not a single one speaks against it, such a theory comes very close to an everyday truth. But in science a “proof” of a theory is not possible, since wrong theories can also produce correct results (see also here). Therefore, in principle, only wrong theories can be refuted. The theory of evolution would be refuted, for example, if one found fossilized rabbits from the Precambrian (an example from the British biologist J.B.S. Haldane); But similar things never happened, all previous fossil finds are compatible with it. However, this restriction means that there can be no definitive truths in science, but only more or less well-documented theories - which, however, must not be confused with the "theories" from everyday use, which are called "hypotheses" in natural science ( reasoned assumptions).

Annotation:

(1) Although the subtitle of Darwin's “On the Origin of Species through Natural Selection” is “The Preservation of Favored Races in the Struggle for Existence”, as the book shows, Darwin understood “race” in the animal-breeding sense of early biology Population with definable characteristics, not - as was the case with the Nazis - as a demarcation based on origin. Today, with modern genetic knowledge (here), Darwin would probably not speak of “race” but of “all individuals with a certain allele” (Dawkins 2009, see literature tips).

Literature tips:

Darwin's main works “A natural scientist's journey around the world”, “About the origin of species ...”, “The descent of man” and “The expression of the emotions in man and animals” are “Collected” at two thousand and one in an inexpensive anthology Works ”published (2006; www.zweitausendeins.de).

The “Journey of a Naturalist Around the World” is also available for lovers of beautiful, bound books under the title “Die Fahrt der Beagle” from Marebuchverlag (2006).

Website:

The complete work of Charles Darwin can be found online at www.darwin-online.org.uk.

The history and impact of Darwin's book "The Origin of Species" is presented in Janet Brown: "About Charles Darwin The Origin of Species" (dtv 2007).

Jürgen Neffe has traced Darwin's journey and reports about it and the development of the theory of evolution in Darwin. The adventure of life (C. Bertelsmann, 2008).

Back to:
evolution

Further in the main article:
The story of life on earth

© Jürgen Paeger 2006–2018

The Animal and plant breeding shows the changes that can be achieved through selection: In a few centuries, the tiny Chihuahua and the Great Dane were bred from wolf-like domestic dogs, and wild cabbage as diverse as cauliflower, kohlrabi, red cabbage and Brussels sprouts.

Darwin dedicated himself to that Barnacles so intensely that his children are said to have once asked a friend for a tour of his house where his father's barnacles were.

The comparisons of embryos are the scientific achievement of the Jena zoologist Ernst Haeckelwho was Darwin's leading supporter in Germany.

Haeckel was an outstanding scientist and gifted artist (see here) who also coined the term “ecology”. On the other hand, he also represented ideas according to which, for example, eliminating selection through medicine would lead to degeneration, and is considered one of the pioneers of eugenics and social Darwinism in Germany (see also box on the left).