Darwin's life

British naturalist and founder of evolution. 1831-1836, as a naturalist, he took part in the voyage around the world sent by Britain and made a five-year scientific investigation. A lot of observation and collection have been made in animals, plants and geology, and after comprehensive discussion, the concept of biological evolution has been formed. 1859 published the Origin of Species, which shocked the academic circles at that time. It is proved by a large number of data in the book that all kinds of creatures are not created by God, but constantly develop and change in heredity, variation, survival competition and natural selection. From simple to complex, from low to high, the theory of biological evolution is put forward, thus destroying all kinds of idealistic creationism and species invariance. Engels listed "evolution theory" as one of the three major discoveries of natural science in19th century (the other two are cell theory, energy conservation and transformation law).

Natural selection and sexual selection put forward by him are consistent and universal theories in current life sciences. Besides biology, his theory is also important to anthropology, psychology and philosophy.

all one's life

First of all, before Darwin

The theory of biological evolution, even the whole biological science, began on1859165438+1October 24th. On that day, after twenty years of careful preparation, Darwin published The Origin of Species. The first edition printed 1250 copies and sold out in one day. A brand-new discipline was born.

However, a new subject will not fall from the sky. 1859, the scientific community had a lot of evidence of evolution, which made preparations for the birth of evolution. The evolutionary evidence at this time can be summarized as animal and plant culture, fossil record, anatomical comparison, degenerated organs, embryonic development and biogeographic distribution.

Animal domestication and plant cultivation have a history of thousands of years, from which people have known that the same species often has very different forms. These forms can be changed, and new varieties can be obtained through careful selection. The varieties obtained by Darwin's so-called "artificial selection" are sometimes more different from each other than wild species. If we see German shepherd dogs and pugs in the wild, it is entirely possible to regard them as two completely different species like wolves and foxes. Animal and plant culture provides perceptual and intuitive materials for "biology is changeable"

At that time, the scientific community had long known that fossils were the remains of living things, and many previous species no longer existed and were extinct, which means that the composition of the biological world has not been static since ancient times. Many species show a trend of gradual change with the passage of geographical time in fossil records, and sometimes transitional fossils can be found between the two groups. The main biological groups do not appear at the same time in the fossil record, but have a first order, and this order is consistent with the order obtained by comparing the existing organisms. For example, from the comparison of morphological structure (such as heart structure) and physiological characteristics (such as respiratory system), we can infer that the order of vertebrates from "low level" to "high level" is fish, amphibian, reptile and mammal, and in the fossil record, we also find that fish fossils really began to appear in earlier strata, followed by amphibians and reptiles, and mammal fossils appeared last. The sequence from "low level" to "high level" shown in fossil records is strong evidence of biological evolution.

As early as the sixteenth century, scientists found that although people and birds are very different in appearance, their bone composition and arrangement are very similar. In the19th century, the comparative anatomy of morphological structures of different biological species has been developed, and the homology of internal structures of various biological species has become more and more obvious. As Darwin pointed out, human hands for grasping, mole forelimbs for digging, horse legs for running, flippers of dolphins for swimming and winged hands of bats for flying are so different in appearance and function, but after removing fur and muscles, the bones presented to us are so similar! The most reasonable explanation for this is that they all evolved from the same ancestor, because they have different functions and different shapes to adapt to the environment, but they have not changed much in their bones. If created separately, it is not necessary for organs with different functions and shapes to have similar structures, because such structural design is sometimes not so reasonable in terms of function and shape. If an engineer is asked to design these forelimbs, he can completely remove some species that are necessary for other species, but they are cumbersome and degenerate to only a trace.

Moreover, comparative anatomy makes us realize that many creatures have some degenerated organs, which is convincing evidence of biological evolution. For example, the whale's hind legs have disappeared, but its hind leg bones have not disappeared. We can also find the pelvis and femur whose tail is no longer working. Even on some snakes, we can find the remains of pelvis and femur. This leads us to believe that whales evolved from land quadrupeds and snakes evolved from lizards. We humans, quite a few organs have completely degenerated, such as coccyx, rotator cuff, appendix, blink membrane (third eyelid) and so on, which have completely degenerated and failed. Besides reminding us that our ancestors once had a monkey-like tail, rabbit-like ears, a herbivore-like cecum and a frog-like blink, can there be any other reasonable explanation?

As early as the18th century, zoologists have discovered that during the development of animal embryos, they will go through a series of periods similar to those of lower animals. For example, people have branchial cleft in the early embryonic development, which is not only like fish in appearance, but also like fish in internal organs: there are arterial arches, and the heart has only two cavities, and so on. The only reasonable explanation for this phenomenon is that people evolved from fish, and the characteristics of ancestors are constantly repeated during embryonic development. In fact, reptiles, birds and mammals are all similar to fish in the early embryonic development, and some periods are almost indistinguishable. This is evidence that all vertebrates have the same ancestor.

Since16th century, with the development of western navigation, especially the discovery of America and Australia, naturalists have seen countless novel species. Many species, even whole genera, families and orders, are found only in a certain geographical area. When naturalists see such unheard-of animals as kangaroos, wombats, marsupials, ferrets and Tasmanian devils in Australia and South America, they can't help wondering why God only created marsupials here. This is not because the environment there is designed for marsupials, because when immigrants bring higher mammals to these places, many marsupials are drastically reduced or even extinct because they cannot compete with higher mammals. Obviously, a more reasonable explanation is that these areas have a unique evolutionary path because they are isolated from other continents. Even an archipelago often has endemic species that cannot be found anywhere else. Darwin, a graduate of a seminary, initially became suspicious of creationism. It is precisely because he saw giant tortoises of different species in the Galapagos Islands and thirteen species of "Darwin finches" that could not be found anywhere else that he couldn't help wondering: Why did God show off his creativity in this small corner and create so many unique species of "only one branch, no branch" here? The reasonable explanation is that the ancestors of these species all came from other places, and after tens of thousands and hundreds of thousands of years of changes, various endemic species have emerged.

In short, before Darwin, biological evolution was irrefutable evidence, and some scientists who dared to break through the shackles of religious beliefs began to face up to this fact. As early as the middle of18th century, French naturalist Buffon thought that biological species were changeable and boldly speculated that all animals came from the same ancestor. He also believes that the age of the earth is much older than thousands of years recorded in the Bible, and links the changes of biological species with the changes of the earth's environment. However, under the pressure of society, Buffon was forced to give up these deviant views, so it failed to have any impact.

Lamarck, another French naturalist later than Buffon, was much more stubborn and influential. He was the first person to systematically study biological evolution. His understanding of biological evolution is different from that of today. In his view, the biological world is a ladder from the simplest and most primitive microorganisms to the most complex and advanced human beings in sequence, and the so-called biological evolution is the process of naturally producing microorganisms from abiotic organisms, and microorganisms evolve into lower organisms, and lower organisms evolve into higher organisms until they evolve into adults. He believes that this evolutionary process is repeated and continues to this day. In other words, to this day, intelligent orangutans are still trying to evolve into adults. Lamarck was also the first person who tried to explain the phenomenon of evolution. He gave the first theory of evolution. There are two main points in this theory: first, the organism itself has an inherent desire to become more and more complex and evolve to a higher form; Second, the living environment can change the morphological structure of organisms, and acquired traits can be inherited. In short, "use it and then discard it". In the famous giraffe example, Lamarck explained the origin of giraffe's long neck like this: giraffe's ancestors often craned their necks to eat tall leaves on trees, and their necks were lengthened by exercise, which is hereditary, so their offspring will be longer than their parents' necks, and their necks will be longer from generation to generation.

Lamarck's theory could not convince scientists at that time to accept the theory of evolution. There are religious reasons, but there are also scientific doubts. For example, Lamarck's theory of evolution holds that abiotic organisms can naturally produce microorganisms, but at that time, although Pasteur had not made a famous experiment to deny the theory of spontaneous production, the scientific community generally believed that there was enough evidence to show that the theory of spontaneous production was incorrect. Therefore, although Lamarck has a great influence, it is often ridiculed and refuted as a negative textbook. There is an urgent need for a scientific giant like Newton in the field of biology. He can undoubtedly prove the fact of biological evolution and give a reasonable explanation. This giant is Darwin.

Second, Darwin

It seems purely accidental that history chose Darwin as the founder of biological science. 1809 Charles Darwin, born in a wealthy doctor's family in February, was an idle dude when he was young, not a genius with a historical mission. His father once accused him: "you don't care about anything but hunting, playing with dogs and catching mice." You will be a disgrace to yourself and your whole family. " Of course, he was very keen on collecting specimens of minerals and insects at this time, but this is a common hobby of boys, and there is nothing special about it, although we can now think that his future scientific research is a continuation of his childhood interest. 1in the autumn of 825, old Darwin was going to let his son inherit the mantle and send him to Edinburgh Medical College. Unfortunately, little Darwin had no interest in medicine, and what was more fatal was that he was too fragile to face the blood dripping on the operating table. Two years later, I had to drop out of medical school. Being a doctor is impossible, and being a priest is also a decent profession. Darwin obeyed his father's orders and went to Cambridge to study theology. Although he is not interested in theology, I'm afraid he spends much more time hunting and collecting beetle specimens than his studies, but he finally graduated from 183 1 and is going to be a country priest for the rest of his life.

When Darwin looked back on his life in his later years, he thought that all his so-called higher education was a complete waste. He finds formal courses boring and never learns anything. But over the years, he met a group of excellent naturalists in his spare time and received their scientific training. His talent in natural history has also been appreciated by these naturalists. 183 1 year, when botanist j·s· Henslow was asked to recommend a young naturalist to take part in the voyage around the world on the beagle, he recommended Darwin. Darwin's father strongly opposed his son's participation in sailing, believing that it would delay his son's development in theology. Under Darwin's repeated entreaties, Old Darwin finally gave in and said that he could go if he could find a respectable person to support him. Darwin found his uncle and future father-in-law to convince his father, and fortunately passed the interview of Captain R. Fitzroy, who is famous for his harshness. 183 1 At the end, he set sail with Beagle, passing through Atlantic Ocean, South America and Pacific Ocean, and inspected geology, animals and plants along the way. Along the way, Darwin made a lot of observation notes, collected countless specimens and shipped them back to England, which provided first-hand information for his future research. Five years later, the Beagle circled the earth and returned to England.

Darwin was a theological graduate and an Orthodox when he set foot on the Beagle, and his piety was often teased by sailors. But when he returned to England, in his view, the Old Testament was only an "obviously false world history", and its reliability was not higher than that of the Hindu holy book. He completely abandoned the Christian faith and gradually became a skeptic or rationalist who did not believe in the existence of God. His starting point was to doubt the belief that "all living things were created by God".

When sailing around the world, there are three sets of facts that make Darwin unable to accept the preaching of creationism: one is the continuity of biological species. He dug up some extinct armadillo fossils in South America, almost the same as the surviving armadillo bones, but much larger. In his view, it can be considered that today's armadillos evolved from this extinct armadillo. Second, the existence of endemic species. When he crossed the South American prairie, he noticed that one kind of ostrich was gradually replaced by another kind of ostrich. Although different, this kind of ostrich was very similar. Each region has different and similar endemic species, which is not so much the result of God's creation as the result of the evolution of the same ancestor in a geographically isolated state. Third, it is evidence from ocean islands. He compared the biota of Cape Verde Islands in Africa and Galapagos Islands in South America. The geographical environment of the two islands is similar. If creatures were created by God, it is reasonable to create similar biological groups in similar geographical environments, but the biological groups of the two islands are very different. The biota of Cape Verde Islands is actually closer to the African continent near it. Obviously, it should be taken into account that the creatures on the island come from the African continent and have gradually changed. This evolutionary process is more obvious in the Galapagos Islands. Darwin found that the islands that make up this archipelago have their own unique turtles, lizards and finches, although their environments are similar. There is no reason to think that God deliberately created these unique species on an island. More reasonably, it should be considered that these unique species evolved from the same ancestor under geographical isolation.

1837, one year after the Beagle sailed, Darwin began to study evolution in secret. His first pile of notes is the variation of animals and plants in domestic and natural environments. He studied all possible materials: personal observations and experiments, other people's papers, communication with biologists at home and abroad, conversations with gardeners and breeders, etc. And soon came to the conclusion that the variation of domestic animals and plants is caused by careful selection of people. But how did the variation in the natural environment come from? He still doesn't know. A year later, he read Malthus's Population Theory in his spare time. Malthus believes that the growth of population is bound to be faster than the growth of means of subsistence, which will inevitably lead to poverty and competition for means of subsistence. Darwin suddenly realized that Malthus' theory could also be applied to biology. The reproductive speed of all living things increases exponentially, and the number of offspring is quite amazing, but the number of a biological group is relatively stable, which shows that only a few offspring can survive, and there is bound to be competition for resources. Darwin further deduced that individuals of any species are different and have variations. These variations may be neutral, and may also affect the viability, leading to the strength of individual viability. In the competition for survival, individuals with strong viability can produce more offspring, races can reproduce, and their genetic traits gradually gain advantages in quantity, while individuals with weak viability are gradually eliminated, which is called "survival of the fittest". As a result, biological species gradually changed because they adapted to the environment. Darwin called this process natural selection.

So in Darwin's view, the origin of giraffe is not the result of recycling, but the variation of long neck in giraffe ancestors. When the environment changes and food is scarce, giraffes with long necks have survival advantages because they can eat the tall leaves on the trees. As a result of selection from generation to generation, the characteristics of long neck spread in the group, and a new species of giraffe was born.

Although Darwin was inspired by reading Population Theory and immediately came up with the idea of natural selection, it was not until four years later that he began to record this theory and sent the manuscript to some friends for advice after collecting a lot of information. He knows very well what kind of shock his theory will bring to society once it is published. As a peace-loving person, this is what he wants to avoid, so he left a will, and his manuscript on evolution can only be published after his death.

But in the summer of 1858, Darwin received a letter from Wallace, forcing him to publish the theory of natural selection before he died. Wallace is a young biogeographer who is visiting the Malay Archipelago. Like Darwin, the geographical distribution characteristics of creatures he observed also prompted him to think about the evolution of creatures. In February of that year, he had an intermittent fever. In his illness, he suddenly thought of Malthus's "population theory", and thus independently discovered the theory of natural selection. He was born in poverty and was extremely opposed to Christianity. He doesn't have Darwin's worries as an upper-class person. Therefore, he spent three nights writing a paper demonstrating natural selection and sent it to Darwin for advice. He didn't know that Darwin had been studying evolution for twenty years at this time, and he discovered Darwin entirely because of his lofty position in biogeography. This position was established after Darwin completed the voyage of Beagle.

When Darwin read Wallace's paper and saw his theory appear in other people's works, his shock and frustration can be imagined. His first thought was to suppress his own achievements and let Wallace enjoy the honor alone. But his friends, geographer Ryle and botanist Hooke, have read his manuscript on natural selection. At their suggestion, Darwin compressed his manuscript into a paper and published it together with Wallace's paper in the Journal of Linnaean Society of 1859. These two papers did not cause much repercussions. It was also at the urging of Ryle and Hooke that Darwin published The Origin of Species in the same year (only about one-third of the manuscript he had prepared for many years), which caused an uproar and conquered the scientific community.

Because the success of the Origin of Species may also be impressed by Darwin's personality and wisdom. Although Wallace and Darwin shared the honor of discovering the theory of natural selection, he always attributed this honor to Darwin and called the theory of natural selection "Darwinism"-a term that is still in use today.

Third, Darwin's three major problems.

Darwin himself called the origin of species a "long debate" and demonstrated two problems: First, species are changeable and organisms are evolutionary. At that time, most biologists who had read the Origin of Species quickly accepted the fact that evolution replaced creationism and became the cornerstone of biological research. Even then, the debate about whether organisms evolved was mainly between biologists and Christian missionaries, not in the field of biology. Second, natural selection is the driving force of biological evolution. Biologists at that time were hesitant to accept this because there were three difficulties in the theory of natural selection at that time.

First, there is a lack of transitional fossils. According to the theory of natural selection, biological evolution is a process of gradual change under the choice of environment, so there should be transitional forms between old species and new species, and between old species and new species, which can only be found in fossils. None of the fossil specimens found at that time can be considered as transitional. Darwin believed that this was due to the incomplete fossil record, and believed that further search would find some transitional fossils. Indeed, two years after the publication of the Origin of Species, the transitional archaeopteryx from reptiles to birds was unearthed, and various transitional fossils were discovered one after another, the most famous of which was the ape-man fossil from apes to humans. There are thousands of transitional fossils now, but compared with millions of known fossils, they are still very rare. There are two reasons for this. On the one hand, biological fossils are formed by accident, so the fossil record must be very incomplete; On the other hand, according to the popular "punctuated equilibrium" hypothesis, when organisms evolve, they often complete the evolution to new species in a short time after a long period of stability, so it is more difficult to form fossils in transitional forms.

Second, earth times. Since natural selection theory holds that biological evolution is a gradual process, it will take a very long time. Darwin believed that this process would take at least hundreds of millions or even billions of years. But william thomson (Lord Kelvin, a creationist), a master of physics at that time, proved by thermodynamic method that the earth was only 1 100 million years old, and only in the last 20 million years at most, the earth was cooled enough for life to survive. Darwin couldn't fight back against the challenge of physicists, just saying, "I'm sure that one day the world will be found to be older than Thomson's calculation." Today, we know that Darwin was right, but Thomson miscalculated. Now, geologists realize that the earth has a history of more than 4 billion years and life was born at least 3 billion years ago. But when it came to the age of the earth, people were obviously more inclined to believe in the authority of physics.

The third difficulty is the most fatal: Darwin could not find a reasonable genetic mechanism to explain natural selection. At that time, biologists generally believed in the so-called "fusion inheritance": the traits of father and mother were fused and passed on to future generations. It seems obvious that the skin color of children born to whites and blacks is always between black and white. According to this, F. Jenkin, a student of Thomson and a Scottish engineer, pointed out that a good mutation will be quickly merged and diluted by many inferior mutations, but it can't be preserved and spread in future generations like the theory of natural selection. Just like a white man marries a black African tribe and has children, his descendants will become completely black after several generations. Although Darwin knew from animal and plant cultures that a good character can be preserved, he did not have a reasonable genetic theory to refute Jane. Darwin was forced to make a concession, and admitted that Lamarckianism of "taking what has been used and discarding it" was also established, which can be used to supplement the theory of natural selection. In fact, before and after Darwin's death (1882), Lamarconism was generally accepted by biologists, while natural selection was doubted.

If Darwin had known about the experiment of Austrian geneticist Mendel, he would not have been in a desperate situation on genetic issues. Mendel discovered the phenomenon of gene separation and independent distribution in 1865. Biological inheritance does not fuse, but is transmitted randomly in units of genes. Therefore, as long as the population is large enough, a genetic trait will not disappear without the influence of external factors (such as natural selection) (the fusion of skin color is a superficial phenomenon under the action of several pairs of genes). Under the action of natural selection, an excellent gene can increase its frequency in the population and gradually spread to the whole population.

Obviously, Mendelianism is the genetic theory that Darwin needed. Unfortunately, Mendel's discovery was completely ignored by the scientific community at that time. Ironically, when Mendelianism was rediscovered in 1900, geneticists thought it declared the death of Darwinism. In their view, random gene mutation, rather than natural selection, is the real driving force of biological evolution. Only some biostatisticians who observe the behavior of wild animals and plants still believe in Darwinism, because the wonderful adaptability of creatures they observe to the environment cannot be explained by random mutation.

Fourth, grand synthesis.

Darwinism and Mendelianism began to merge, twenty years after Mendelian law was rediscovered. This time, the giant of science is not alone, but the stars are bright. Among these great scientists, the most important ones are British R.A. Fisher, J.B.S Hald and American S.Wright. They proved theoretically that Darwinism and Mendelianism not only do not conflict, but also complement each other. The evolutionary data obtained by biostatisticians who observe and study in this field can be deduced from the principles of genetics. On the basis of Mendelian genetics, natural selection can perfectly explain the adaptive evolution of organisms, without Lamarconism at all (Lamarconism has also been proved impossible at this time). Mendelian genetics is what Darwin dreamed of! These theoretical studies began at 19 18 and were basically completed in the early 1930s. 1930, Fisher published the genetic theory of natural selection. 193 1 year, Wright published Evolution in Mendel Population. 1932, Holden published Evolutionary Dynamics. These three classic works constitute the theoretical basis of modern evolution.

However, these theoretical studies involve complex mathematical calculations, which are beyond the understanding of ordinary biologists. Moreover, the theory without experiments is hard to be accepted by biologists. Therefore, their research work did not have much influence in the biology field at that time. Until another great scientist appeared in the field of biology. He not only has the patience to understand these complicated mathematical calculations, but also verifies them with experiments. He is an American geneticist of Russian descent, T. Dobzhansky. Dubzansky studied Drosophila genetics with Russian geneticist S. Chetverikov and immigrated to the United States in 1927 (two years later, his teacher was arrested by the Soviet government and his laboratory was closed). He cooperated with Wright and confirmed Wright's theoretical work with fruit flies as experimental materials. 1937, Dubzhansky published Genetics and the Origin of Species. In this most important book on evolution after the Origin of Species, Dubzansky unified the theory of natural selection and Mendelian genetics theoretically and experimentally, which had a great influence on naturalists and experimental biologists and stimulated biologists in various fields to devote themselves to the study of evolution.

The next decade will be a fruitful decade of modern evolution. Zoologist E. Mayr applied modern evolution theory to taxonomic research, and put forward a model for the emergence of new species under the conditions of geographical variation and isolation. Paleontologist G.G. Simpson's research shows that modern evolutionary theory can be used to explain fossil records, while botanist G.L. stebbins pointed out that the evolution of plants can also be explained by modern evolutionary theory. By the 1940s, modern evolutionism had been successfully applied to all fields of biology. 1942, Sir Julian Sorell Huxley (the grandson of thomas huxley, one of the founders of evolution) published Evolution: Modern Synthesis, which integrated the research results of modern evolution in various fields, so modern evolution was called "Modern Synthesis Theory", that is, neo-Darwinism. The final completion of this great comprehensive process was marked by the establishment of the "Committee on the same problems of genetics, taxonomy and paleontology" in Princeton in 1947. The thirty academic authorities who make up this committee represent different fields of biology, but they share the same view: the integration of Darwinism and Mendelianism.

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