Read Ebook {PDF EPUB} and the Theory of Evolution by by Fred Bortz Evolution Theories Before Darwin. The concepts of evolution and natural selection have very long histories, with the first theories preceding Darwin and Wallace’s by thousands of years. Earlier Lifeforms Gave Birth to Humans. At the dawn of scientific thought in Ancient Greece, about 2600 years ago, a visionary by the name of Anaximander mulled over the origins of human beings. In the end, he decided humans could not have appeared on Earth in their current form. Meet your ancestor – according to Anaximander. Anaximander’s reasoning was that the young of some animals can look after themselves from the time they are born. Human children, however, need to be cared for for many years. If this had always been the case, humans could not have survived. Anaximander speculated that our ancestor may have been a fish-like creature which gave birth to humans after they had reached an age when they could survive without parents to look after them. He believed the world’s first lifeforms originated in the world’s wetter environments, then spread to the drier regions. and Monsters. About a century after Anaximander, a scientifically minded Ancient Greek philosopher by the name of Empedocles hit upon the theory of natural selection. Empedocles pictured the earth in its early days populated by strange creatures – cattle with human heads, arms without shoulders, and all sorts of other monstrous creatures. These strange lifeforms became extinct, Empedocles said. Only the better adapted survived. Although Empedocles had devised a crude theory of natural selection, he did not realize that the process might lead to the evolution of entirely new . He thought it had simply operated at one time to remove freakish creatures. Linnaeus and Hybrids. Now fast forward many centuries from Empedocles to less than 300 years ago. By that time the Age of Enlightenment had begun to take a firm hold among educated people in Europe and North America. In 1744 the great natural scientist Carl Linnaeus proposed that God originally made just a few starting species on an island. Over time, these starting species interbred, producing hybrids, resulting in a much broader range of species. Buffon and a Single Source of Living Creatures. In 1753 Comte de Buffon proposed a single source for all creatures with four legs. From this single ancestor, Buffon said: Having had this novel idea, Buffon then promptly dismissed it as incorrect! Hutton Offers a Clear Statement of Natural Selection. In 1794 the founder of modern geology – James Hutton – stated the principles of natural selection unambiguously. Darwin Takes Center Stage – but not Charles. Erasmus Darwin was Charles Darwin’s grandfather. Erasmus lived in a time when reproduction was less well understood than today. He believed that fathers provided the ‘filament’ which became the embryo. No part of the embryo was contributed by the mother. The mother’s role was to provide the growing embryo with: a home (this could be a womb or an egg) nutrients (via placenta or egg yolk) oxygen. Erasmus Darwin’s view of evolution comes rather close to his more famous grandson’s. In his 1794 book Zoonomia , Erasmus Darwin appears to suggest it’s possible that all warm-blooded animals have a common origin. The common origin is a filament which evolves over time by its own actions. It’s an interesting thought experiment to replace the concept of ‘filament’ with the concept of DNA. He then goes further, suggesting that over a large number of years there has been a progression of living creatures beginning with plants, then some types of animals, then other types of animals. All of this life has a common origin. When considering how nature decided which male would father a new generation, Erasmus Darwin expresses the view that a species is improved by competition between males – a ‘survival of the fittest’ argument: Charles Darwin read his grandfather’s Zoonomia while at university and admired it. Later, though, he said it disappointed him, because there was too much speculation and too few facts. Lamarck and Lamarckism. In 1800 Jean-Baptiste Lamarck proposed a coherent but wrong theory of evolution. Lamarck proposed that offspring inherit the characteristics their parents use most. A giraffe that stretched high for leaves would produce offspring with longer necks. Or if your parents worked out often at the gym, you would be born with the ability to become more muscular than if they had spent all their time watching TV. Lamarck believed evolution was a slow, gradual process. William Wells – A Clear Statement of Natural Selection. In 1813 read a paper to the Royal Society. In it he stated that different breeds of domestic animals are produced by people selecting the best animals to breed from. Then, discussing selection in humans, he said: “[it] seems to be done with equal efficiency, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit. Of the accidental varieties of man, which would occur among the first scattered inhabitants, some one would be better fitted than the others to bear the diseases of the country. This race would multiply while the others would decrease …” Unfortunately, Wells does not make the obvious step (for modern readers) of applying the principle of natural selection to other species. He published his work in 1818. Darwin gave credit to Wells in later editions of Origin of Species , but was unaware of Well’s work while he was working on his own theory. Geoffroy Saint-Hilaire, Evolution in Large Steps, Birds Arising from . Geoffroy Saint-Hilaire believed that all organisms are related at a deep level. In 1831 he penned a paper with the title Memoir on the Degree to Which the Environment Influences Animal Form . He believed that events in the environment could cause the sudden production of a new species from an existing species. Saint-Hilaire wondered – decades before the discovery of Archaeopteryx – whether birds had been produced by an evolutionary leap from reptiles. Although this sounds remarkably modern, Saint-Hilaire’s theory required a to lay an egg that produced a bird. Nevertheless, his insight was impressive. Grant, Lyell and a Common Origin for all Living Things. In Charles Darwin’s time, some British scientists, including Robert Edmond Grant and Charles Lyell, while rejecting Lamarckism, began to believe all lifeforms had the capacity to transform into other species. They noted that the geologic record appeared to show a progression of lifeforms. Robert Edmond Grant – who had taught Darwin at the University of Edinburgh – even proposed a common origin for plants and animals, as Darwin’s grandfather had. However, neither Grant nor Lyell could propose a coherent mechanism for the transformation of species. Edward Blyth and Natural Selection. In 1835 Edward Blyth clearly described how breeders use artificial selection to produce domestic animals to meet specific requirements. He also described how in nature animals appear with slight variations. He identified that the process we now call natural selection would operate on the variations. However, he didn’t notice that this could lead to the formation of new species. In fact, he believed the opposite was true. Blyth thought natural selection would serve to keep animals true to their original form by removing variations that worked less well than the original species. He did not make the intuitive leap that some variations might be better suited to the environment than the original. In 1837 Blyth finally seemed to realize that some variations might be better suited to the environment than the original species, writing: Unfortunately, rather than answering yes to his own question, he answered no! He still thought natural selection preserved rather than produced species. Robert Chambers and a Sensational Bestseller about Evolution. In 1844 an anonymous author (revealed after his death to be the publisher and geologist Robert Chambers) published a blockbuster of a book entitled Vestiges of the Natural History of Creation . The book’s ideas went wholly against the religious views of the day, saying the solar system had formed naturally from a nebula and that life had been spontaneously generated on the earth. The lowly forms of life had then evolved into higher forms, including man. However, Chambers did not offer a viable mechanism for evolution. Although the science behind the book was sketchy, it captured the imagination of its many readers. As much as the public enjoyed the book, the churches condemned it. Scientists, including Charles Darwin, deplored the book for its – as they saw it – half-baked science. The bickering surrounding the book may have increased Darwin’s reluctance to publish his own theory of evolution by natural selection, which he had formulated in rough form as early as 1839. On the other hand, as Darwin later acknowledged, the book also prepared some people’s minds for the ideas he expressed in his Origin of Species . Darwin and Wallace’s Theory of Evolution by Natural Selection. On July 1, 1858, a joint paper was read to the Linnean Society. The authors were Charles Darwin and . The paper told the world of their theory which came to be known as evolution by natural selection. The following year, Darwin released his historic book with large amounts of evidence supporting the new theory. By the 1870s the role of evolution in the formation of new species had been accepted by scientists. Many scientists, however, refused to believe that evolution’s driving force was natural selection. Acceptance of this by mainstream biologists only came in the 1930s. This followed publication of Ronald Fisher’s book The Genetical Theory of Natural Selection . In this work Fisher united the previously incompatible heredity concept of Gregor Mendel with the natural selection concept of Darwin and Wallace. Author of this page: The Doc Images digitally enhanced and colorized by this website. © All rights reserved. Further Reading Erasmus Darwin Zoonomia; or, The Laws of Organic Life J. Johnson, London 1794. Charles Darwin The Origin of Species, 6th Edition John Murray, London, 1872. Jonathan Barnes The Presocratic Philosophers Routledge, 2002. Phillip Sloan The Concept of Evolution to 1872 The Stanford Encyclopedia of Philosophy (Fall 2014 Edition), Edward N. Zalta (ed.) More from FamousScientists.org: Comments. Thank you very much for giving me most best information about evolution. thank you for this. i’ve got a project on evolution and i had no idea all this happened before darwin. Essay On Charles Darwin's Theory Of Evolution. However, there are some differences within their arguments. Wallace’s outlook on natural selection and varying individual characteristics greatly relied on the individual’s adaptation for its environment for surival (for example, the bird “capable of very rapid and long continued flight” page 5). Darwin’s outlook the same topic greatly related to species competition for survival. Nonetheless, both outlooks as described in these papers focus on natural selection but it is important to notice the difference in perspectives. Other notable differences in arguments presented in these papers were the topics of sexual selection, and artificial selection – which were only by Darwin.… Analysis Of Charles Darwin's Theory Of Evolution. In 1859 Charles Darwin published his book “The Origin of Species”. This book explained his theories of how animals and humans were formed. The beginning of the earth has been a mystery frustrating the minds of scientist for many years. Darwin’s Theory of Evolution is a change in the genetic material of a population of organisms from one generation to the next. Though changes produced in one generation are normally small, differences with each generation overtime can become substantial changes in population.… Survival Of The Fittest: On The Origin Of Species By Charles Darwin. Charles Darwin was an English naturalist and geologist. He is best known for his theory of evolution. Darwin learned most of his information on the Voyage of the Beagle. Charles Darwin wrote a book, On the Origin of Species. From this book, came the the saying “Survival of the Fittest.” Darwin also came up with natural selection.… Charles Darwin And John Locke And The Human Race. However, The Origins of Species is considered the root of modern biology because it explained how the human race has evolved over time. This book explains how all the species have evolved and changed over time, including the human race. This book is mainly based on a trip that Darwin took, when he went to the Galapagos Island. Over there, Darwin started to observe different species native to the islands. Darwin realized that the species were unique to the island, but with some similarities in the way they look physically, Darwin also noticed that each species was perfectly adapted to its environment.… Charles Darwin's On The Origins Of Species. This passage is found in paragraph six, Chapter IV of Charles Darwin`s On the Origins of Species. Diverse groups of animals evolve from one or a few common ancestors and the mechanism by which this evolution takes place is natural selection are main points of the evaluation theory, which explains in the book of On the Origins of Species by Charles Darwin, the father of evolution, a modest and affable scientist who believed true about the origins of adaptation, diversity, and complexity among the living forms on Earth. In his book, he tried to puzzle out the process that lead to such diversity and adaptation. In 1858, both Charles Darwin and Alfred Russel Wallace simultaneously published the same theory that species evolve through natural selection,… Essay On Darwin's Theory Of Evolution. Alfred Russel Wallace and Charles Darwin were once friends, contemporaries, and rivals. Both scientists proposed the theory of natural selection, the process where organisms develop traits over time that adapt to their surrounding environments and become more common through reproduction. Darwin published his work On the Origin of Species detailing his theory of natural selection in 1859, while Wallace had discussed with Darwin the theory as well. The theory of natural selection led Darwin and Wallace to develop radically different views of evolution that rivaled each other's theories. Darwin published his theories of evolution, and as a result, they were widely known throughout his time.… Comparing Darwin And Lamarck's Theories Of Evolution. He proposed that after periodic catastrophic floods new species were created or produced. Although also in the pre-Darwinian nineteenth century in England, Robert Chambers, was an evolutionary thinker that published Vestiges of the Natural History of Creation to open up the question of evolution by natural law. Since this publication was so controversial it was not until after his death that he was revealed to be the author. Chambers theory of how evolution occurred was similar to Lamarck’s original theory, although made some belittling remarks of Lamarck. His theory included two main ideas that he perceived from the evidence.… Darwin's Theory Of Evolution. Indeed, many organisms have common traits and characteristics, but this still doesn't mean that they are related. Darwin's theory, which all organisms descend from one ancestor, is the result of a study in which he travelled to many places around the world and studied different organisms from different places. His conclusion is based on his observations of various organisms and his study of fossils. To begin with, if whales and humans have… Charles Darwin Contributions. Contributions of Charles Darwin Charles Robert Darwin was a British scientist best known for his contributions to the evolutionary theory and his theory of natural selection. Darwin came up with these theories in the late 1830s, but failed to publish them until the release of his book the Origin of Species in 1859. With pressure building from colleagues and scientists in the Far East, it is said that Darwin decided to rush publishing his findings. Charles Darwin’s theory of evolution was constructed during a period of industrialization that was taking hold in Britain and the United States. Society during this time was looking to science to answer questions that had troubled the world for centuries.… Charles Darwin's Theory Of Evolution Essay. Emergence of the idea of Evolution The Webster’s dictionary definition of evolution is stated as the historical development of a biological group. Due to advancements in scientific thinking and ideas from different ancient cultures such as the Arabs, Indians, and Chinese, notions of biological evolution were able to be cultivated long before prominent naturalist, Charles Darwin was even born. Precursors to the development of the theory of evolution were largely important for naturalists to understand the many forms of life on Earth. In an epistemological standpoint, before early naturalists could begin to understand the forms of life they had to organize them by listing and describing them. There were numerous naturalists that discovered… Darwin’s Theory of Evolution in 5 Easy Points. The theory of evolution is one of the most widely accepted ways to explain all life on earth. At its center is how biology directs the evolution of species to create diversity and change in the natural world. Today, the centerpiece of the theory of evolution is that of natural selection by Charles Darwin. It was initially published in 1859 in his book, On the Origin of Species . It would take many years to be accepted, however eventually, and until now, it is the basis of describing the biological world. Since then, it has been carefully studied by generations of biologists. Many have broken down and provided more detail for Darwin’s theories. One of the most well-known, explained and extended Darwin’s theory by dividing it into five parts. This article will break Darwin’s theory of evolution down into easy to understand points. It will also discuss the parts of the theory that have been proven, and those that are still controversial. Evolution of species at a glance. In short, Darwin’s theory of evolution is the process of natural selection by which nature selects the fittest, best-adapted organisms to reproduce, multiply and survive. It is also called adaptation, where traits most likely to help an individual survive are labeled adaptive. As organisms change and new variants thrive, species emerge, and evolve. Five principles of Darwin’s theory of evolution. Darwin’s theory can be broken into points that describe its core principles. Mayr’s was a professor at Harvard University. His five principles outline the way and circumstances that evolution of species to occur. In this article, we will break up his explanations of evolution. They help to show the parts that are true and not true. 1. A world of constant change. When you look at a flock of birds at the park you’re seeing a tiny snapshot in time. A few moments later, they will have flown away. In 10 years, many will have died and had offspring that. Perhaps the birds change the colors of their feathers in 100 years from now. The most basic aspect of the theory of evolution is that life is not stagnant. Nature, the environment, and everything that lives in it are in a fluid, state of flux. In Darwin’s time, it was debated as to whether changes to species could occur at all. Alongside others like Lamarck and Buffon, Darwin’s work forwarded the idea that a species CAN change over time. You can observe the steady state (a bird in the park), but thousands of years before, it could have been a different species altogether. Darwin wasn’t the original person to suggest this idea. Many had suggested changes to species, each of the other experts had different opinions as to how it happened. They all agreed that a species has the inner ability to change and evolve. The Origin of Species represents an enormous shift in thinking in human history. 2. The common ancestor. If the world is in constant change, it has to have changed from something. Darwin needed to take a big leap in thinking for his theory of evolution to take hold. Where did life come from? He deduced that all creatures on earth should have come from one or a few sources. It went beyond Lamarck’s idea that complex creatures evolved from simpler ones. The theory is both accepted and controversial. On one side it is thought that life does come from one or a few sources. A common ancestor has not, however, been identified as yet. It’s believed that simple versions of DNA or RNA based viruses could be one of the main branches. However, socially Darwin’s theory brings up more contention. At the time it was thought that humans were separate from the animal world. A privileged lineage would not come from the same source as all other creatures. Today, it’s not proven whether all life did evolve from one ancestor. Biologists today are still grappling whether the evolution of species comes from a single source. The idea is generally accepted, however, that life on earth does come from one or a few ancestors. 3. Gradual change and species formation. The evolution of species argues a philosophy of science known as gradualism. It discusses whether changes on earth happen quickly or on a slower, much longer scale. Darwin’s push for a gradual change was against Lamarck’s idea that species-wide change could happen in a few generations. Gradual change has been both validated and shown to be inaccurate. One proof is the estimate of how old the earth was. In Darwin’s time, it was thought the planet was much younger. He contended that earth had to be older, based on the many species of life. Later, a Scottish geologist proved him correct when he found the earth is far older than geologists had estimated. Darwin’s prediction was right on a geological scale. However, in the world of microbes, it has since shown that evolution of species can happen much faster. In bacteria and insects, single generation change is known to occur. In sexual species (mammals and larger creatures), things are more gradual, but still, do occur in sudden bursts. Two famous evolutionists, Stephen Gould & Richard Dawkins, debated the points of punctuated equilibrium or a gradual change due to DNA mutations. Gould’s idea of punctuated equilibrium was seen more as a model of sudden bursts of change. Punctuated equilibrium can be observed when environmental disasters bring large-scale change. Life and species need to adapt to harsh conditions speeding the process of change up. Evolution of species was said to happen slowly over vast spans of time. However, today it is known to have a faster component. 4. Inheriting change across a species. Evolution of species had a big problem to explain how such massive diversity of life on earth came to be. For example, let’s think of giraffes with long necks. Lamarck described his explanation that giraffes living under a tree with leaves would grow long necks to reach the leaves. Darwin said that some are born with long necks that would spread through the population. Eventually, a new species, with long necks evolved. Lamarck’s idea was that each would have to undergo separate, internal change. Darwin’s theory says that within a population, changes occur as the balance of new inherited traits spread across the population. It differs from Lamarck’s idea that each in the population must undergo the same change. How a new species comes about was something that Darwin struggled with his entire life. In his trip to the Galapagos, he found three new species of mockingbirds on different islands. Each similar, yet distinct species, where Darwin could observe the process. He concluded geography had created new distinct species. Species evolution is the distinct way that a new creature comes to exist. Darwin’s model showed that members of the same population were being selected due to individual characteristics. A species must first have variation, then environment to select. While widely accepted today the exact mechanism of how species evolve is still not wholly explained through genetics. The mechanism may lie in epigenetics and shift in DNA. 5. Evolution by Natural Selection. Of his work, natural selection was the most unique of Darwin’s ideas. It deals with the competition or struggles for life as the driver for success or extinction of a species. Other naturalists previously discussed these. Darwin took the idea a step further. He described the change within a species. For a giraffe with a longer neck, the advantage continues because it can reach more food. It is stronger, lives longer and produces more offspring. The children are born with a long neck, and the cycle continues. Natural selection relies on other points to be true: Reproductive surplus: more offspring are created than needed. Discrete determinants of heredity: These are now known to be genes held in DNA. Individual heritable differences: Now understood to be genes passed by parents to their offspring. Natural selection is now the most widely used way to describe adaption. The evolution of a species occurs with its inner genetic potential and the environment. There are two scenarios that differ, that is sexual selection and animal breeding. In nature, creatures are subject to the randomness of the process. Natural selection took a long time to be accepted. This is mainly due to its mechanical nature. It stripped any deterministic aspect of how species will evolve due to the fate of random chance. However, natural selection has two steps: Chance of the surrounding world or the outside pressure Non-chance or inner genetic potential to produce a solution for adaption. Both of these factors work together to form natural selection. It is this arm of Darwin’s theory that biologists use to explain the harmony of adaption. Species are flowing with the surroundings, in motion with their genetic code. It is also the arm of evolution that has stripped the purpose of life. More popularly used by ‘Neo-Darwinists,’ who explain a machine like nature to existence. Conclusion: While being our best answer, evolution by natural selection is still a theory with arms to be researched. Darwin’s theory of evolution remains the best model to explain the natural world. It can be broken into many aspects that need to be explained in its own right. Today we can look with the advantage of retrospect with scientific progress to confirm or direct further understanding. Each has both factual and philosophical discussions, of which some are open-ended. Now it’s up to you. Do you think Darwin’s theory explains the natural world today? Leave your answers in the comment section below. 18.1B: Charles Darwin and Natural Selection. Charles Darwin and Alfred Wallace independently developed the theories of evolution and its main operating principle: natural selection. Explain how natural selection can lead to evolution. Key Points. Wallace traveled to Brazil to collect and observe insects from the Amazon rainforest. Darwin observed that finches in the Galápagos Islands had different beaks than finches in South America; these adaptations equiped the birds to acquire specific food sources. Wallace and Darwin observed similar patterns in the variation of organisms and independently developed the same explanation for how such variations could occur over time, a mechanism Darwin called natural selection. According to natural selection, also known as “survival of the fittest,” individuals with traits that enable them to survive are more reproductively successful; this leads to those traits becoming predominant within a population. Natural selection is an inevitable outcome of three principles: most characteristics are inherited, more offspring are produced than are able to survive, and offspring with more favorable characteristics will survive and have more offspring than those individuals with less favorable traits. Key Terms. natural selection : a process in which individual organisms or phenotypes that possess favorable traits are more likely to survive and reproduce descent with modification : change in populations over generations. Charles Darwin and Natural Selection. In the mid-nineteenth century, the mechanism for evolution was independently conceived of and described by two naturalists: Charles Darwin and Alfred Russel Wallace. Importantly, each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world to places like South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, as with Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands west of Ecuador. On these islands, Darwin observed that species of organisms on different islands were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape. The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the mainland of South America. Darwin imagined that the island species might be modified from one of the original mainland species. Upon further study, he realized that the varied beaks of each finch helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, while insect-eating finches had spear-like beaks for stabbing their prey. Figure \(\PageIndex \): Beak Shape Among Finch Species : Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources. Natural Selection. Wallace and Darwin observed similar patterns in other organisms and independently developed the same explanation for how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection, also known as “survival of the fittest,” is the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits. This leads to evolutionary change, the trait becoming predominant within a population. For example, Darwin observed that a population of giant tortoises found in the Galapagos Archipelago have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks. In times of drought, when fewer leaves would be available, those that could reach more leaves had a better chance to eat and survive than those that could not reach the food source. Consequently, long-necked tortoises would more probably be reproductively successful and pass the long-necked trait to their offspring. Over time, only long-necked tortoises would be present in the population. Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, most characteristics of organisms are inherited, or passed from parent to offspring, although how traits were inherited was unknown. Second, more offspring are produced than are able to survive. The capacity for reproduction in all organisms outstrips the availability of resources to support their numbers. Thus, there is competition for those resources in each generation. Both Darwin and Wallace were influenced by an essay written by economist Thomas Malthus who discussed this principle in relation to human populations. Third, Darwin and Wallace reasoned that offspring with the inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over successive generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment; it is the only mechanism known for adaptive evolution. Papers by Darwin and Wallace presenting the idea of natural selection were read together in 1858 before the Linnean Society in London. The following year, Darwin’s book, On the Origin of Species , was published. His book outlined his arguments for evolution by natural selection. Figure \(\PageIndex \): Charles Darwin and Alfred Wallace : Both (a) Charles Darwin and (b) Alfred Wallace wrote scientific papers on natural selection that were presented together before the Linnean Society in 1858. Charles Darwin’s Concept of Natural Selection: 5 Criticism Points with Neo- Darwinism. Charles Darwin’s concept of natural selection was explained clearly and convincingly by him in his masterpiece—The Origin of Species’ (The full title of the book was ‘On the Origin of Species by Means of Natural Selection’ or The Preservation of Favoured Races in the Struggle for Life) in 1859. Its essence is that the animal and the plant worlds came into existence by a process of dynamic descent. Darwin’s explanation of the way in which evolution occurs may be generalized as follows. The change in species by the survival of an organismal type exhibiting a natural variation that gives it an adaptive advantage in an environment, thus, leading to a new environmental equilibrium, is evolution by natural selection. Thus natural selection is a con​tinuous process of trial and error on a gigantic scale, for all of living matter is involved. It includes the following element. 1. The universal occurrence of variation: The difference between individuals within a popula​tion of a species constitutes variations. Variations are the characteristic of every group of animals and plants and there are many ways in which organisms may differ. Due to the variations some individuals would be better adjusted towards the surroundings than the others. Adaptive modifications are caused through the struggle for existence. According to Darwin, the varia​tions are continuous and those which are helpful in the adaptations of an organism towards its surroundings would be passed on to the next generation, while the others disappear. 2. Over production (rapid multiplication): Every species, in the absence of environmental checks, tends to increase in a geometrical manner. If a population of a given species doubles in one year and if there are no checks on its increase, it will quadruple the next year, and so on. A salmon produces 28,000 eggs in a season. A female rabbit gives birth to six young ones in one litter and produces four litters in a year. Six-month old rabbit is capable of reproduction. If all the rabbit survives and multiplies at this rate, their number would be very large after some time. Darwin calculated that even a pair of elephants which are about the slowest breeding animals known, could in the absence of any checks, have 29 million descendants at the end of 800 years. Thus, more organisms of each kind are born than can possibly obtain food and survive. Since the number of each species remains fairly constant under natural conditions, it must be as​sumed that most of the offsprings in each generation perish. If all the offsprings of any species remained alive and reproduced they would soon crowd all other species from the earth. 3. Struggle for existence: Since more individuals are born than can survive there is an intraspecific of interspecific or environmental struggle for survival, a competition for food, mates and space. (a) Intraspecific struggle is among the members of the same species. It is the keenest form of struggle for existence because the requirements of life are identical for the combatants. (b) Interspecific struggle is the one waged between the members of different species. This is best seen in a newly exposed land where to begin with might be counted the seedlings of at least 20 different species of plants but ultimately seedlings of 2 or 3 species grow to matu​rity. That is to say, these 2 or 3 species have survived where the other 17 or 18 could not. (c) Environmental struggle is the struggle between the organism and the environment in which it is placed. Natural catastrophes like earthquakes, tidal waves, bursting of volca​noes are all causes for killing large populations of many species of animals and plants. 4. Survival of the fittest: In this struggle for existence as we have seen few survive: majority dies out. This is explained as being due to the fact those few which survive have necessary advan​tageous variations which though small have been of a high survival value to the individual concerned, i.e., such of them as are fit to survive have survived and such of them as are unfit for survival have perished. This idea of “the survival of the fittest” is the core of the theory of natural selection. 5. Inheritance of useful variations: The organisms after getting fitted to the surroundings trans​mit their useful variations to the next generation, while the non-useful variations are elimi​‐ nated. Darwin could not differentiate between continuous and discontinuous variations. Hence, upto some extent, he agreed with Lamarck’s views, because according to Darwin acquired characters which are useful to the possessor could be inherited. Darwin considered that useful variations are transmitted to the offspring and appear more prominently in succeeding generations. After some generations these continuous and gradual variations in the possessor would be so distinct that they form a new species. Criticism of the Natural Selection Theory : 1. While natural selection theory explains survival of the fittest, it does not explain the arrival of the fittest. Thus, to give rise to such specializations as elaborate mimicry, or the electric organ of the torpedo, etc., which are of apparent advantage only in the perfected state, natural selection, acting only upon minute gradations towards perfections, seems inadequate. 2. Over-specialization of some organs like tusks of elephants, antlers of deer have developed so much that instead of providing usefulness to the possessor they often give hindrance to them. These organs or body structures should not have reached a harmful stage, if natural selection was operating. However, such cases of overspecializations have been explained by Darwin on the basis of discontinuous variations or “sports” which, according to him, do not play any role in evolution. 3. Natural selection cannot account for degeneracy—To say an organ is no longer useful and, hence, disappears, is to state the effect and not the cause. 4. One of classical objections to natural selection is that new variations would be lost by “dilu​tion” as the individuals possessing them bred with others without them. We now know that although the phenotypic expression of a gene may be altered when it exists in combination with certain other genes, yet the gene itself is not altered and is transmitted to succeeding generations. 5. Darwin indirectly accepted the Lamarckian idea of inheritance of acquired characters in the form of pangenesis hypothesis, which cannot be accepted in the light of present knowledge of genetics. Neo-Darwinism : Neo-Darwinism is a modified form of Darwinism. The Neo-Darwinians like T.H. Huxley, Herbert Spencer, D.S. Jordan, Asa Gray, E. Haeckel and A. Wiesmann believed that natural selection has accounted everything that is involved in evolution. Certain Neo-Darwinians such as A. Wiesmann and his followers rejected Darwin’s theory except its principal element of natural selection. These Neo-Darwinians, though distinguished between gerinplasm and somatoplasm of living organisms in their germplasm theory, yet they could not appreciate the role of mutations in evolution. Neo-Darwinians thought that adaptations result from multiple forces and natural selections is only one of these many forces in contrast to Darwin’s belief who held that adaptations result mainly by a single source, i.e., natural selection Neo-Darwinians also believed that characters are not inherited as such but there are character determiners, the determinants or biophores, which control only the development. The ultimate character would result out due to the interaction of the determiners, activity of the organism and the environment during development. Thus, Neo-Darwinism was incomplete and partly wrong because it lacked present understanding of genetics.