Query Id: tqa2:L_0432
Run: ReRank2_BERT
In 1859, Charles Darwin placed the whole theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, and provided observational evidence that it had done so. This changed the attitudes of most exponents of the scientific method. Darwin's discoveries revolutionised the zoological and botanical sciences, by introducing the theory of evolution by natural selection as an explanation for the diversity of all animal and plant life. The subject-matter of this new science, or branch of biological science, had been neglected: it did not form part of the studies of the collector and systematist, nor was it a branch of anatomy, nor of the physiology pursued by medical men, nor again was it included in the field of microscopy and the cell theory. Almost a thousand years before Darwin, the Arab scholar Al-Jahiz (781 – 868) had already developed a rudimentary theory of natural selection , describing the Struggle for existence in his Book of Animals where he speculates on how environmental factors can affect the characteristics of species by forcing them to adapt and then passing on those new traits to future generations. However, his work had largely been forgotten, along with many other early advances of Arab scientists, and there is no evidence that his works were known to Darwin.
Thus punctuated equilibrium contradicts some of Darwin's ideas regarding the specific mechanisms of evolution, but generally accords with Darwin's theory of evolution by natural selection.
Precise mechanisms of reproductive heritability and the origin of new traits remained a mystery. Towards this end, Darwin developed his provisional theory of pangenesis. In 1865, Gregor Mendel reported that traits were inherited in a predictable manner through the independent assortment and segregation of elements (later known as genes). Mendel's laws of inheritance eventually supplanted most of Darwin's pangenesis theory. August Weismann made the important distinction between germ cells that give rise to gametes (such as sperm and egg cells) and the somatic cells of the body, demonstrating that heredity passes through the germ line only. Hugo de Vries connected Darwin's pangenesis theory to Weismann's germ/soma cell distinction and proposed that Darwin's pangenes were concentrated in the cell nucleus and when expressed they could move into the cytoplasm to change the cells structure. De Vries was also one of the researchers who made Mendel's work well-known, believing that Mendelian traits corresponded to the transfer of heritable variations along the germline. To explain how new variants originate, de Vries developed a mutation theory that led to a temporary rift between those who accepted Darwinian evolution and biometricians who allied with de Vries. In the 1930s, pioneers in the field of population genetics, such as Ronald Fisher, Sewall Wright and J. B. S. Haldane set the foundations of evolution onto a robust statistical philosophy. The false contradiction between Darwin's theory, genetic mutations, and Mendelian inheritance was thus reconciled.
While he did not originate the term, Charles Darwin identified the argument as a possible way to falsify a prediction of the theory of evolution at the outset. In The Origin of Species (1859), he wrote, "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case." Darwin's theory of evolution challenges the teleological argument by postulating an alternative explanation to that of an intelligent designer—namely, evolution by natural selection. By showing how simple unintelligent forces can ratchet up designs of extraordinary complexity without invoking outside design, Darwin showed that an intelligent designer was not the necessary conclusion to draw from complexity in nature. The argument from irreducible complexity attempts to demonstrate that certain biological features cannot be purely the product of Darwinian evolution.
The voyage of the Beagle brought the survey ship HMS Beagle, under captain Robert FitzRoy, to the Galápagos on 15 September 1835 to survey approaches to harbours. The captain and others on board, including his companion, the young naturalist Charles Darwin, made observations on the geology and biology on Chatham, Charles, Albemarle and James islands before they left on 20 October to continue on their round-the-world expedition. Primarily a geologist at the time, Darwin was impressed by the quantity of volcanic craters they saw, later referring to the archipelago as "that land of craters." His study of several volcanic formations over the 5 weeks he stayed in the islands, led to several important geological discoveries, including the first, correct explanation for how volcanic tuff is formed. Darwin noticed the mockingbirds differed between islands, though he thought the birds now known as Darwin's finches were unrelated to each other, and did not bother labelling them by island. Nicholas Lawson, acting Governor of Galápagos for the Republic of the Equator, met them on Charles Island, and as they walked to the prison colony, Lawson told Darwin the tortoises differed from island to island. Towards the end of the voyage, Darwin speculated that the distribution of the mockingbirds and the tortoises might "undermine the stability of Species". When specimens of birds were analysed on his return to England, it was found that many apparently different kinds of birds were species of finches, which were unique to islands. These facts were crucial in Darwin's development of his theory of natural selection explaining evolution, which was presented in The Origin of Species.
Subsequently, on the voyage of the Beagle, Darwin found that nature was not so beneficent, and the distribution of species did not support ideas of divine creation. In 1838, shortly after his return, Darwin conceived his theory that natural selection, rather than divine design, was the best explanation for gradual change in populations over many generations. He published the theory in On the Origin of Species in 1859, and in later editions, he noted responses that he had received:
On the voyage of the Beagle the young Charles Darwin took a break between graduating and starting his career as a clergyman to study the natural history of South America, an interest he had developed at the University of Edinburgh and the University of Cambridge. Influenced by Charles Lyell's Principles of Geology, he became an able geologist as well as collecting plant and animal specimens, and fossils of gigantic extinct mammals. By the return journey, he was connecting patterns of geographical and historical distribution, and starting to doubt the stability of Species. In September 1838 he conceived his theory of natural selection as the cause of evolution, then as well as developing his career as a geologist and writer worked privately on finding evidence and answering possible objections, and set out his ideas in an essay written in 1844. He discussed transmutation with his friend Joseph Dalton Hooker, who read the essay in 1847. After turning his attention to biology and completing eight years of work on barnacles, Darwin intensified work on his theory of species in 1854.
The book was in the library of HMS Beagle for Charles Darwin's voyage. In The Origin of Species (1859), in a chapter on the difficulties facing the theory, Darwin comments that "The expression of conditions of existence, so often insisted on by the illustrious Cuvier, is fully embraced by the principle of natural selection." Darwin continues, reflecting both on Cuvier's emphasis on the conditions of existence, and Jean-Baptiste Lamarck's theory of acquiring heritable characteristics from those Cuvieran conditions: "For natural selection acts by either now adapting the varying parts of each being to its organic and inorganic conditions of life; or by having adapted them during long-past periods of time: the adaptations being aided in some cases by use and disuse, being slightly affected by the direct action of the external conditions of life, and being in all cases subjected to the several laws of growth. Hence, in fact, the law of the Conditions of Existence is the higher law; as it includes, through the inheritance of former adaptations, that of Unity of Type."
The Aldabra giant tortoise has an unusually long history of organized conservation. Albert Gunther of the British Museum, who later moved to the Natural History Museum of London (enlisting Charles Darwin and other famous scientists to help him) worked with the government of Mauritius to establish a preserve at the end of the 19th century. The related, but distinct, species of giant tortoise from the Seychelles islands (Seychelles giant tortoise A. g. hololissa and Arnold's giant tortoise A. g. arnoldi) are the subject of a captive-breeding and reintroduction program by the Nature Protection Trust of Seychelles.
Giant tortoises are among the world's longest-living animals, with an average lifespan of 100 years or more. The Madagascar radiated tortoise Tu'i Malila was 188 at death in Tonga in 1965. Harriet (initially thought to be one of the three Galápagos tortoises brought back to England from Charles Darwin's Beagle voyage but later shown to be from an island not even visited by Darwin) was reported by the Australia Zoo to be 176 years old when she died in 2006. Also, on 23 March 2006, an Aldabra giant tortoise named Adwaita died at Alipore Zoological Gardens in Kolkata. He was brought to the zoo in the 1870s from the estate of Lord Clive and is thought to have been around 255 years old when he died. Around the time of its discovery, they were caught for food in such large quantities that they became virtually extinct by 1900. Giant tortoises are now under strict conservation laws and are categorised as threatened species.
Giants of the Galápagos was opened in 2009 to coincide with the 200th birthday of Charles Darwin, and is home to five Galápagos giant tortoises: a male named Dirk and four females named Dolly, Dolores, Polly and Priscilla. The exhibit features a large indoor area, with a heated pond and underfloor heating, while the outdoor paddock has been designed to mimic the tortoise's natural environment and features two heated pools, one of which is a naturalistic clay wallow.
Darwin's finches provide a good example of divergent evolution, where some 15 species diverged from a single species of finch that arrived on the Galapagos islands.
Although not the only species in the family the Darwin's finches are the only ones in the family to be found in the archipelago. Famous for inspiring Darwin in his theory of evolution, the finches have astonishingly different beaks.14 species in Galápagos
Darwin's finches are different closely related species which Darwin discovered on the Galapagos Islands. Darwin's voyage on the Beagle, and the finches in particular, are known to have influenced his thinking so that he would later produce a basic theory of evolution by natural selection. Darwin reasoned that there had to be a common ancestor. Later, extensive research was done by Peter and Rosemary Grant. The birds are all about the same size (10–20 cm). They mainly differ in the form of the beak. The beak is adapted to the food they eat. The birds are all brownish or black. They have short rounded wings and a rounded tail that often appears cocked to one side. Most male finch mature to a solid black color, while the females mature to a drab grayish color. Exceptions are made for the Vegetarian and Tree Finches the males never become completely black rather they have a black head, neck and upper breast. Warbler, Woodpecker and Mangrove Finches have more of an olive color.
Before the time of Charles Darwin's work and life, animal and plant scientists had already used selective breeding. Darwin added to that body of work with his scientific observations about the ability of science to change species. These accounts contributed to Darwin's theory of natural selection.
Charles Darwin coined the term 'selective breeding'; he was interested in the process as an illustration of his proposed wider process of natural selection. Darwin noted that many domesticated animals and plants had special properties that were developed by intentional animal and plant breeding from individuals that showed desirable characteristics, and discouraging the breeding of individuals with less desirable characteristics.
Darwin's barnacle studies convinced him that variation arose constantly and not just in response to changed circumstances. In 1854, he completed the last part of his Beagle-related writing and began working full-time on evolution. His thinking changed from the view that species formed in isolated populations only, as on islands, to an emphasis on speciation without isolation; that is, he saw increasing specialisation within large stable populations as continuously exploiting new ecological niches. He conducted empirical research focusing on difficulties with his theory. He studied the developmental and anatomical differences between different breeds of many domestic animals, became actively involved in fancy pigeon breeding, and experimented (with the help of his son Francis) on ways that plant seeds and animals might disperse across oceans to colonise distant islands. By 1856, his theory was much more sophisticated, with a mass of supporting evidence.
In 1859, Charles Darwin placed the whole theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, and provided observational evidence that it had done so. This changed the attitudes of most exponents of the scientific method. Darwin's discoveries revolutionised the zoological and botanical sciences, by introducing the theory of evolution by natural selection as an explanation for the diversity of all animal and plant life. The subject-matter of this new science, or branch of biological science, had been neglected: it did not form part of the studies of the collector and systematist, nor was it a branch of anatomy, nor of the physiology pursued by medical men, nor again was it included in the field of microscopy and the cell theory. Almost a thousand years before Darwin, the Arab scholar Al-Jahiz (781 – 868) had already developed a rudimentary theory of natural selection , describing the Struggle for existence in his Book of Animals where he speculates on how environmental factors can affect the characteristics of species by forcing them to adapt and then passing on those new traits to future generations. However, his work had largely been forgotten, along with many other early advances of Arab scientists, and there is no evidence that his works were known to Darwin.
The major sticking point for many in the question of human evolution was whether human mental faculties could have possibly been evolved. The gap between humans and even the smartest ape seemed too large, even for those who were sympathetic to Darwin's basic theory. Alfred Russel Wallace, the co-discoverer of evolution by natural selection, believed that the human mind was too complex to have evolved gradually, and began over time to subscribe to a theory of evolution that took more from Spiritualism than it did the natural world. Darwin was deeply distressed by Wallace's change of heart, and much of the Descent of Man is in response to opinions put forth by Wallace. Darwin focuses less on the question of whether humans evolved than he does on showing that each of the human faculties considered to be so far beyond those of beasts—such as moral reasoning, sympathy for others, beauty, and music—can be seen in kind (if not degree) in other animal species (usually apes and dogs).
The 1859 publication of Darwin's theory in On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life is often considered the central event in the history of modern biology. Darwin's established credibility as a naturalist, the sober tone of the work, and most of all the sheer strength and volume of evidence presented, allowed Origin to succeed where previous evolutionary works such as the anonymous Vestiges of Creation had failed. Most scientists were convinced of evolution and common descent by the end of the 19th century. However, natural selection would not be accepted as the primary mechanism of evolution until well into the 20th century, as most contemporary theories of heredity seemed incompatible with the inheritance of random variation.