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Experiments in Plant Hybridization (1865)
by Gregor Mendel
Read at the meetings of February 8th, and March 8th, 1865

Introductory Remarks

Experience of artificial fertilization, such as is effected with ornamental plants in order to obtain new variations in color, has led to the experiments which will here be discussed. The striking regularity with which the same hybrid forms always reappeared whenever fertilization took place between the same species induced further experiments to be undertaken, the object of which was to follow up the developments of the hybrids in their progeny.

To this object numerous careful observers, such as K�lreuter, G�rtner, Herbert, Lecoq, Wichura and others, have devoted a part of their lives with inexhaustible perseverance. G�rtner especially in his work Die Bastarderzeugung im Pflanzenreiche , has recorded very valuable observations; and quite recently Wichura published the results of some profound investigations into the hybrids of the Willow. That, so far, no generally applicable law governing the formation and development of hybrids has been successfully formulated can hardly be wondered at by anyone who is acquainted with the extent of the task, and can appreciate the difficulties with which experiments of this class have to contend. A final decision can only be arrived at when we shall have before us the results of detailed experiments made on plants belonging to the most diverse orders.

Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of the hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations.

It requires indeed some courage to undertake a labor of such far-reaching extent; this appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the history of the evolution of organic forms.

The paper now presented records the results of such a detailed experiment. This experiment was practically confined to a small plant group, and is now, after eight years' pursuit, concluded in all essentials. Whether the plan upon which the separate experiments were conducted and carried out was the best suited to attain the desired end is left to the friendly decision of the reader.

Gregor Mendel

Gregor Johann Mendel (20 July 1822 � 6 January 1884) was an Austrian Augustinian priest and scientist often called the "father of modern genetics" for his study of the inheritance of traits in pea plants. Mendel showed that the inheritance of traits follows particular laws, which were later named after him. The significance of Mendel's work was not recognized until the turn of the 20th century. Its rediscovery prompted the foundation of genetics.

Biography

Mendel was born into a German-speaking family in Hynčice, Austrian Silesia, Austria (now Czech Republic), and was baptized two days later. He was the son of Anton and Rosine Mendel and had one elder and also a younger sister. During his childhood, Mendel worked as a gardener, studied beekeeping, and as a young man attended the Philosophical Institute in Olomouc. Upon recommendation of his physics teacher Friedrich Franz, he entered the Augustinian Abbey of St. Thomas in Brno in 1843. Born Johann Mendel, he took the name Gregor upon entering monastic life. In 1851 he was sent to the University of Vienna to study, returning to his abbey in 1853 as a teacher, principally of physics.

Gregor Mendel, who is known as the "father of modern genetics", was inspired by both his professors at university and his colleagues at the monastery to study variation in plants, and he conducted his study in the monastery's garden. Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants (i.e. Pisum sativum). This study showed that one in four pea plants had purebred recessive alleles, two out of four were hybrid and one out of four were purebred dominant. His experiments brought forth two generalisations which later became known as Mendel's Laws of Inheritance.

Mendel read his paper, "Experiments on Plant Hybridization", at two meetings of the Natural History Society of Br�nn in Moravia in 1865. When Mendel's paper was published in 1866 in Proceedings of the Natural History Society of Br�nn, it had little impact and was cited about three times over the next thirty-five years. His paper received plenty of criticism at the time, but is now considered a seminal work.

After Mendel completed his work with peas, he turned to experimenting with honeybees, to extend his work to animals. He produced a hybrid strain (so vicious they were destroyed), but failed to generate a clear picture of their heredity because of the difficulties in controlling mating behaviours of queen bees.

Elevated as abbot in 1868, his scientific work largely ended as Mendel became consumed with his increased administrative responsibilities, especially a dispute with the civil government over their attempt to impose special taxes on religious institutions.

At first Mendel's work was rejected (and it was not widely accepted until after he died). The common belief at the time was that pangenes were responsible for inheritance. Even Darwin's theory of evolution used pangenesis instead of Mendel's model of inheritance. The modern synthesis uses Mendelian genetics.

Mendel died on 6 January 1884, in Brno, Austria-Hungary (now Czech Republic), from chronic nephritis.


Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation

Rediscovery of Mendel's work

It was not until the early 20th century that the importance of his ideas was realized. In 1900, his work was rediscovered by Hugo de Vries and Carl Correns. Though Erich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understand Mendel's laws.[citation needed] Mendel's results were quickly replicated, and genetic linkage quickly worked out. Biologists flocked to the theory, even though it was not yet applicable to many phenomena, it sought to give a genotype understanding of heredity which they felt was lacking in previous studies of heredity which focused on phenotypic approaches. Most prominent of these latter approaches was the biometric school of Karl Pearson and W.F.R. Weldon, which was based heavily on statistical studies of phenotype variation. The strongest opposition to this school came from William Bateson, who perhaps did the most in the early days of publicising the benefits of Mendel's theory (the word "genetics", and much of the discipline's other terminology, originated with Bateson). This debate between the biometricians and the Mendelians was extremely vigorous in the first two decades of the twentieth century, with the biometricians claiming statistical and mathematical rigor, whereas the Mendelians claimed a better understanding of biology. In the end, the two approaches were combined as the modern synthesis of evolutionary biology, especially by work conducted by R. A. Fisher as early as 1918.

Mendel's experimental results have later been the object of considerable dispute. Fisher analyzed the results of the F1 (first filial) ratio and found them to be implausibly close to the exact ratio of 3 to 1.[4] Only a few would accuse Mendel of scientific malpractice or call it a scientific fraud � reproduction of his experiments has demonstrated the validity of his hypothesis � however, the results have continued to be a mystery for many, though it is often cited as an example of confirmation bias. This might arise if he detected an approximate 3 to 1 ratio early in his experiments with a small sample size, and continued collecting more data until the results conformed more nearly to an exact ratio. It is sometimes suggested that he may have censored his results, and that his seven traits each occur on a separate chromosome pair, an extremely unlikely occurrence if they were chosen at random. In fact, the genes Mendel studied occurred in only four linkage groups, and only one gene pair (out of 21 possible) is close enough to show segregation distortion; this is not a pair that Mendel studied.

The standard botanical author abbreviation Mendel is applied to species he described.

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Experiments on Plant Hybridization

Written in 1865 by Gregor Mendel, Experiments on Plant Hybridization (German: Versuche �ber Pflanzen-Hybriden) was the result after years spent studying genetic traits in pea plants. Mendel read his paper to the Natural History Society of Brunn (Brno) on 8 February and 8 March 1865. It was published in the Proceedings of the Society the following year.

In his paper, Mendel compared seven discrete characters:



    * Color and smoothness of the seeds (grey and round or white and wrinkled)
    * Color of the cotyledons (yellow or green)
    * Color of the flowers (white or violet)
    * Shape of the pods (full or constricted)
    * Color of unripe pods (yellow or green)
    * Position of flowers and pods on the stems
    * Height of the plants (short or tall)

Through experimentation, Mendel discovered that one inheritable trait would invariably be dominant to its recessive alternative. This model, later known as Mendelian inheritance or Mendelian genetics, provided an alternative to blending inheritance, which was the prevailing theory at the time. Mendel's work received little attention from the scientific community and was largely forgotten. It was not until the early 20th century that Mendel's work was rediscovered and his ideas used to help form the modern synthesis.

In 1936, the statistician R.A. Fisher used a chi-square test to analyze Mendel's data and concluded that Mendel's results with the predicted ratios were far too perfect, indicating that adjustments (intentional or unconscious) had been made to the data to make the observations fit the hypothesis. Later authors have claimed Fisher's analysis was flawed, proposing various statistical and botanical explanations for Mendel's numbers. It is also possible that Mendel's results are "too good" merely because he reported the best subset of his data � Mendel mentioned in his paper that the data was from a subset of his experiments.

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Alfred Russel Wallace

Alfred Russel Wallace OM, FRS (8 January 1823 � 7 November 1913) was a British naturalist, explorer, geographer, anthropologist and biologist.

He did extensive fieldwork first in the Amazon River basin, and then in the Malay Archipelago, where he identified the Wallace line dividing the fauna of Australia from that of Asia. He is best known for independently proposing a theory of natural selection which prompted Charles Darwin to publish his own more developed and researched theory sooner than intended. Wallace was also one of the leading evolutionary thinkers of the 19th century who made a number of other contributions to the development of evolutionary theory, including the concept of warning colouration in animals, and the Wallace effect. He was also considered the 19th century�s leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography".

Wallace was strongly attracted to radical ideas. His advocacy of spiritualism and his belief in a non-material origin for the higher mental faculties of humans strained his relationship with the scientific establishment, especially with other early proponents of evolution. He was critical of what he considered to be an unjust social and economic system in 19th century Britain, and was one of the first prominent scientists to raise concerns over the environmental impact of human activity.

Early evolutionary thinking

Unlike Darwin, Wallace began his career as a travelling naturalist already believing in the transmutation of species. The concept had been advocated by Jean-Baptiste Lamarck, Geoffroy Saint-Hilaire, Erasmus Darwin, and Robert Grant, among others. It was widely discussed, but not generally accepted by leading naturalists, and was considered to have radical, even revolutionary connotations. Prominent anatomists and geologists such as Georges Cuvier, Richard Owen, Adam Sedgwick, and Charles Lyell attacked it vigourously. It has been suggested that Wallace accepted the idea of the transmutation of species in part because he was always inclined to favour radical ideas in politics, religion and science and because he was unusually open to marginal, even fringe ideas in science.

He was also profoundly influenced by Robert Chambers' work Vestiges of the Natural History of Creation, a highly controversial work of popular science published anonymously in 1844 that advocated an evolutionary origin for the solar system, the earth, and living things. Wallace wrote to Henry Bates in 1845:

    I have a rather more favourable opinion of the �Vestiges� than you appear to have. I do not consider it a hasty generalization, but rather as an ingenious hypothesis strongly supported by some striking facts and analogies, but which remains to be proven by more facts and the additional light which more research may throw upon the problem. It furnishes a subject for every student of nature to attend to; every fact he observes will make either for or against it, and it thus serves both as an incitement to the collection of facts, and an object to which they can be applied when collected.

Wallace deliberately planned some of his field work to test the hypothesis that under an evolutionary scenario closely related species should inhabit neighbouring territories. During his work in the Amazon basin he came to realize that geographical barriers�such as the Amazon and its major tributaries�often separated the ranges of closely allied species, and he included these observations in his 1853 paper "On the Monkeys of the Amazon". Near the end of the paper he asks the question "Are very closely allied species ever separated by a wide interval of country?"

In February 1855, while working in the state of Sarawak on the island of Borneo, Wallace wrote "On the Law Which has Regulated the Introduction of Species", a paper which was published in the Annals and Magazine of Natural History in September 1855. In this paper he gathered and enumerated general observations regarding the geographic and geologic distribution of species (biogeography). His conclusion that "Every species has come into existence coincident both in space and time with a closely allied species" has come to be known as the "Sarawak Law". Wallace thus answered the question he had posed in his earlier paper on the monkeys of the Amazon river basin. Although it contained no mention of any possible mechanisms for evolution, this paper foreshadowed the momentous paper he would write three years later.

The paper shook Charles Lyell's belief that species were immutable. Although his friend Charles Darwin had written to him in 1842 expressing support for transmutation, Lyell had continued to be strongly opposed to the idea. Around the start of 1856 he told Darwin about Wallace's paper, as did Edward Blyth who thought it "Good! Upon the whole!� Wallace has, I think put the matter well; and according to his theory the various domestic races of animals have been fairly developed into species." Despite this hint, Darwin mistook Wallace's conclusion for the progressive creationism of the time and wrote that it was "nothing very new� Uses my simile of tree [but] it seems all creation with him." Lyell was more impressed, and opened a notebook on species where he grappled with the consequences, particularly for human ancestry. For the first time Darwin now spelt out the full details of natural selection to Lyell, and although Lyell could not agree, he urged Darwin to publish to establish priority. Darwin demurred at first, then began writing up a species sketch of his continuing work in May 1856.

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Charles Darwin

Charles Robert Darwin (12 February 1809 � 19 April 1882) was an English naturalist. After becoming eminent among scientists for his field work and inquiries into geology, he proposed and provided scientific evidence that all species of life have evolved over time from one or a few common ancestors through the process of natural selection. The fact that evolution occurs became accepted by the scientific community and the general public in his lifetime, while his theory of natural selection came to be widely seen as the primary explanation of the process of evolution in the 1930s, and now forms the basis of modern evolutionary theory. In modified form, Darwin's scientific discovery remains the foundation of biology, as it provides a unifying logical explanation for the diversity of life.

Darwin developed his interest in natural history while studying first medicine at Edinburgh University, then theology at Cambridge. His five-year voyage on the Beagle established him as a geologist whose observations and theories supported Charles Lyell's uniformitarian ideas, and publication of his journal of the voyage made him famous as a popular author. Puzzled by the geographical distribution of wildlife and fossils he collected on the voyage, Darwin investigated the transmutation of species and conceived his theory of natural selection in 1838. Having seen others attacked as heretics for such ideas, he confided only in his closest friends and continued his extensive research to meet anticipated objections. In 1858, Alfred Russel Wallace sent him an essay describing a similar theory, causing the two to publish their theories early in a joint publication.

His 1859 book On the Origin of Species established evolution by common descent as the dominant scientific explanation of diversification in nature. He examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals. His research on plants was published in a series of books, and in his final book, he examined earthworms and their effect on soil.

In recognition of Darwin's pre-eminence, he was buried in Westminster Abbey, close to John Herschel and Isaac Newton.


The voyage of the Beagle

Second voyage of HMS Beagle

The second voyage of HMS Beagle from 27 December 1831 to 2 October 1836 was the second survey expedition of HMS Beagle, under captain Robert FitzRoy who had taken over command of the ship on its first voyage after her previous captain committed suicide. FitzRoy, fearing the same fate, sought a gentleman companion for the voyage. The student clergyman Charles Darwin took the opportunity, making his name as a naturalist and becoming a renowned author with the publication of his journal which became known as The Voyage of the Beagle.

The Beagle sailed across the Atlantic Ocean then carried out detailed hydrographic surveys around the coasts of the southern part of South America, returning via Tahiti and Australia having circumnavigated the Earth. While the expedition was originally planned to last two years, it lasted almost five.

Darwin spent most of this time exploring on land; three years and three months on land, 18 months at sea. His work made his reputation as a geologist and collector of fossils, and his detailed observations of plants and animals provided the basis for ideas which he later developed into his theory of evolution by natural selection.


A watercolour by HMS Beagle's draughtsman, Conrad Martens. Painted during the survey of Tierra del Fuego, it depicts native Fuegians hailing the Beagle

Voyage

Beagle was originally scheduled to leave on 24 October 1831 but because of delays in her preparations the departure was delayed until December. She attempted to depart on 10 December but ran into bad weather. Finally, on 27 December at 2:00 pm, the Beagle left Plymouth harbour on what was to become a groundbreaking scientific expedition. After completing extensive surveys in South America she returned via New Zealand to Falmouth, Cornwall, England on 2 October 1836.

It touched at Madeira for a confirmed position without stopping, then went on to Tenerife but there was quarantine because of cholera in England and they were denied landing. They continued on to make their first stop at the volcanic island of St. Jago in the Cape de Verd Islands, and it is here that Darwin's Journal starts. While readings were taken to accurately confirm the longitude, he went on shore being fascinated by his first sight of tropical vegetation and the geology with a high white band of seashells supporting Lyell's thesis of gradual rising and falling of the earth's crust.

Darwin had been given the first volume of Charles Lyell's Principles of Geology by FitzRoy when they set out, the book explaining landforms as the outcome of gradual processes over huge periods of time, and on their first stop ashore at St Jago the features he saw gave him a revolutionary insight into the geological history of the island, inspiring him to think of writing a book on the subject. Darwin later wrote of "seeing a thing never seen by Lyell, one yet saw it partially through his eyes".

After touching at more islands they arrived at Bahia (Salvador), Brazil on 29 February where Darwin was enraptured by the tropical forest. He found the sight of slavery offensive and made the mistake of responding when FitzRoy remarked on it being justifiable, with the result that FitzRoy lost his temper and banned Darwin from his company. The officers had nicknamed their captain "hot coffee" for such outbursts, and within hours FitzRoy apologised and asked Darwin to remain.

The ship made its way down the coast to Rio de Janeiro. Customarily the ship's surgeon took the position of naturalist. Robert McCormick, the Beagle's surgeon, quite reasonably felt he was being supplanted, as the gentleman Darwin received all the invitations from dignitaries onshore, and was sufficiently disgruntled to leave the ship here. Darwin now assumed the quasi-official duties of naturalist, getting nicknamed Philos, though his collections were his own and were shipped back to Henslow in Cambridge to await his return. Several others on board including the new acting-surgeon and FitzRoy made sizeable collections for the Crown, which the Admiralty placed in the British Museum.

Surveying South America

As the Beagle carried out its survey work, going to and fro along the coast, Darwin spent much of the time away from the ship. At intervals the Beagle returned to ports where mail could be received and Darwin's notes, journals and collections were sent back to England. Darwin made long journeys inland, with travelling companions from the locality. In Patagonia he rode inland with gauchos and saw them use bolas to bring down "ostriches" (rheas), and ate roast armadillo.

With the Beagle anchored at Bahia Blanca, Darwin and FitzRoy were sailing about ten miles (16 km) across the bay on 22 September 1832 when they saw fossilised bones of extinct gigantic mammals on the beach at Punta Alta, in strata suggesting quiet tidal deposits rather than a catastrophe.[8] Darwin returned with Covington to excavate over several days, and found a huge skull which seemed to him to be related to the African rhinoceros. At first, he thought that fragments of bony armour came from a gigantic armadillo like the small creatures common in the area. When he used Bory de Saint-Vincent's Dictionnaire classique to identify a jawbone and tooth he found nearby as belonging to the Megatherium he was excited to note that the only specimens in Europe were locked away in the Kings collection at Madrid, but as Cuvier's descriptions of those specimens wrongly suggested the creatures were armoured, this misled Darwin into thinking that the armour belonged to the Megatherium.

At Montevideo in November the mail from home included a copy of the second volume of Lyell's Principles of Geology, which set out a variation of Creationism relating to the idea of gradual change, with species being formed at "centres of creation" then going extinct as the environment changed to their disadvantage.

They reached Tierra del Fuego on 1 December 1832 and Darwin was taken aback at the crude savagery of the natives, in stark contrast to the civilised behaviour of the three Fuegians they were returning as missionaries (who had been given the names York Minster, Fuegia Basket and Jemmy Button). He described his first meeting with the native Fuegians as being "without exception the most curious and interesting spectacle I ever beheld: I could not have believed how wide was the difference between savage and civilised man: it is greater than between a wild and domesticated animal, inasmuch as in man there is a greater power of improvement." In contrast, he said of Jemmy that "It seems yet wonderful to me, when I think over all his many good qualities, that he should have been of the same race, and doubtless partaken of the same character, with the miserable, degraded savages whom we first met here. (Four decades later, in The Descent of Man he would use his impressions from this period as evidence that man had evolved civilization from a more primitive state.)

At the island of "Buttons Land" on 14 January 1833 they set up a mission post, with huts, gardens, furniture and crockery, but when they returned nine days later the possessions had been looted and divided up equally by the natives. Matthews gave up, rejoining the ship and leaving the three civilised Fuegians to continue the missionary work. The Beagle went on to the Falkland Islands arriving just after the 1833 invasion. Darwin studied the relationships of species to habitats and found ancient fossils like those he'd found in Wales. Fitzroy bought a schooner to assist with the surveying, and they returned to Patagonia where this was fitted with a new copper bottom and renamed Adventure. Darwin was assisted by the young sailor Syms Covington in preserving specimens and his collecting was so successful that with FitzRoy's agreement he took on Covington as a full time servant for �30 a year.

The two ships sailed to the R�o Negro in Argentina where Darwin left the Beagle for another journey inland with the gauchos. On 13 August 1833 he met General Juan Manuel de Rosas who was then leading a punitive expedition against native "Indians", and obtained a passport from him. As they crossed the pampas the gauchos told Darwin of a rare smaller species of Rhea. At Bahia Blanca, waiting for the Beagle, he revisited Punta Alta and found bones of another megatherium, this time undisturbed in situ in a context of layers of sediments including modern shells that indicated that the climate had not changed much since their extinction, with no signs of a sudden catastrophic flood. More expeditions inland almost ended disastrously when Darwin fell ill then became entangled in a revolution as rebels allied to Rosas blockaded Buenos Aires, but the passport helped and with Covington he managed to escape in a boatload of refugees. They rejoined the Beagle at Montevideo. As surveys were still in progress Darwin set off on another 400 mile (600 km) "galloping" trip via Mercedes, Buenos Aires near the Uruguay River. On 22 November he was told of "giant's bones" in a farmyard and bought a hippopotamus sized fossil skull for eighteen pence then carried it 120 miles (190 km) back to Montevideo. This would be the first fossil identified by Richard Owen, an extinct giant capybara which Owen named Toxodon.

At the Beagle, the artist Augustus Earle left due to health problems and was replaced by Conrad Martens. They sailed south, putting in at Port Desire on 23 December. Here Martens shot a rhea which they enjoyed eating before Darwin realised that this was the smaller species, and preserved the remains. In January 1834, 110 miles (180 km) further south, they reached Port St Julian and exploring the local geology in cliffs near the harbour Darwin found fossils of pieces of spine and a hind leg of "some large animal, I fancy a Mastodon". On 26 January they entered the Straits of Magellan and at St. Gregory's Bay they met half-civilised Patagonian "giants" over 6 ft (1.8 m) tall, described by Darwin as "excellent practical naturalists" who explained to him that the smaller rheas were the only species this far south, while the larger rheas kept to the north, the species meeting around the Rio Negro.

After further surveying in Tierra del Fuego they returned on 5 March 1834 to visit the missionaries, but found the huts deserted. Then canoes approached and they found that one of the savage natives was Jemmy, who had lost his possessions and had settled into the native ways, taking a wife. Darwin had never seen "so complete & grievous a change". Jemmy came on board and dined using his cutlery properly, speaking English as well as ever, then assured them that he "had not the least wish to return to England" and was "happy and contented", leaving them gifts of otter skins and arrowheads before returning to the canoe to join his wife. Of the first visit Darwin had written that "Viewing such men, one can hardly make oneself believe that they are fellow-creatures, and inhabitants of the same world. It is a common subject of conjecture what pleasure in life some of the less gifted animals can enjoy: how much more reasonably the same question may be asked of these barbarians.", yet one of these savages had readily adapted to civilisation and then chosen to return to his primitive ways. This did not sit comfortably with the Cambridge don's view of mankind as the highest creation, immeasurably superior to the animals.

They returned to the Falkland Islands on 16 March just after an uprising of gauchos and Indians had butchered British nationals, and helped to put the revolt down. Darwin received word from Henslow that his specimens had reached Cambridge, with the South American fossils being fabulously prized and displayed before the cream of British science, making Darwin's reputation. The Beagle now sailed to southern Patagonia, and on 19 April an expedition including FitzRoy and Darwin set off to take boats as far as possible up the river Rio Santa Cruz in Santa Cruz Province, Argentina from Puerto Santa Cruz, with all involved taking turn in teams dragging the boats upstream. The river cut through a series of rises then plateaux forming wide plains covered with shells and shingle, and Darwin discussed with FitzRoy his interpretation that these terraces had been shores that had gradually raised in accordance with Lyell's theories. They approached the Andes but had to turn back.

West coast of South America

The Beagle and Adventure now surveyed the Straits of Magellan before sailing north round up the west coast, reaching the island of Chilo� in the wet and heavily wooded Chonos Archipelago on 28 June 1834. They then spent the next six months surveying the coast and islands southwards. At Valparaiso on 23 July 1834. Darwin bought horses and set off up the volcanic Andes, but on his way back down fell ill and spent a month in bed. It is possible that he contracted Chagas' disease here, leading to Charles Darwin's illness after his return, but this diagnosis of his symptoms is disputed.

He learnt that the Admiralty had reprimanded FitzRoy for buying the Adventure. FitzRoy had taken it badly, selling the ship and announcing they would go back to recheck his survey, then had resigned his command doubting his sanity, but was persuaded by his officers to withdraw his resignation and proceed. The artist Conrad Martens left the ship and took passage to Australia.

After waiting for Darwin the Beagle sailed on 11 November to survey the Chonos Archipelago. From here they saw the eruption of the volcano Osorno in the Andes. They then sailed north arriving at the port of Valdivia on 20 February 1835. Darwin was on shore when he experienced an earthquake, and returned to find the port town badly damaged. Two hundred miles (320 km) north at Concepci�n, Chile, they found the city devastated by repeated shocks and a tidal wave, with even the cathedral in ruins. Turning away from the horrors of death and destruction, Darwin noticed that mussel beds now lay above high tide with the shellfish dead. There was clear evidence of the ground rising some 9 ft (2.7 m), and he had actually experienced the gradual process of the continent emerging from the ocean as Lyell had indicated.

Back in Valparaiso, Darwin set out on another trek up the Andes and on 21 March reached the continental divide at 13,000 ft (4,000 m): even here he found fossil seashells in the rocks. After going on to Mendoza they were returning by a different pass when they found a petrified forest of fossilised trees, crystallised in a sandstone escarpment showing him that they had been on an Pacific beach when the land sank, burying them in sand which had been compressed into rock, then had gradually been raised with the continent to stand at 7,000 ft (2,100 m) in the mountains. On returning to Valparaiso with half a mule's load of specimens he wrote to his father that his findings, if accepted, would be crucial to the theory of the formation of the world. After another gruelling expedition in the Andes while the Beagle was refitted he rejoined it and sailed to Lima, but found an armed insurrection in progress and had to stay with the ship. Here he was writing up his notes when he realised that Lyell's idea that coral atolls were on the rims of rising extinct volcanoes made less sense than the volcanoes gradually sinking so that the coral reefs around the island kept building themselves close to sea level and became an atoll as the volcano disappeared below. This was a theory he would examine when they reached such islands.

Gal�pagos Islands

A week out of Lima, they reached the Gal�pagos Islands on 15 September 1835. On Chatham Island Darwin found broken black rocky volcanic lava scorching under the hot sun with volcanic craters which reminded him of the iron foundries of industrial Staffordshire. He noted widespread thin scrub thickets of only ten species, and very few insects. The impressive giant tortoises to his fancy appeared antediluvian, though apparently he thought at the time that these had been brought to the islands by buccaneers for food.

At the prison colony on Charles Island he was told that tortoises differed from island to island, but this was not obvious on the islands he visited and he did not bother with collecting their shells. The Marine Iguanas seemed hideously ugly, and due to mislabelling in the museum he thought these unique creatures were a South American species. The birds were remarkably unafraid of humans, and of unique kinds with some resemblance to South American species. He noticed that mockingbirds differed with islands and took care with labelling them, but did not bother to note where other species such as finches had been found. Fortunately others were being more methodical in labelling their collections. They left on 20 October.

Tahiti to Australia

They sailed on, dining on Galapagos tortoises, and on 9 November sighted the Low Islands which at first appeared uninteresting to Darwin, just white beaches and palm trees. On Tahiti he soon found interest in luxuriant vegetation and the pleasant intelligent natives who showed the benefits of Christianity, refuting allegations he had read about tyrannical missionaries overturning indigenous cultures.

On 19 December they reached New Zealand where Darwin thought the tattooed Māori to be savages with character of a much lower order than the Tahitians, and noted that they and their homes were "filthily dirty and offensive". He saw missionaries bringing improvement in character as well as new farming practices with an exemplary "English farm" employing natives. Richard Matthews was left here with his elder brother Joseph Matthews who was a missionary at Kaitaia. Darwin and FitzRoy were agreed that missionaries had been unfairly misrepresented in tracts, particularly one written by the artist Augustus Earle which he had left on the ship. Darwin also noted many English residents of the most worthless character, including runaway convicts from New South Wales. By 30 December he was glad to leave New Zealand.

The first sight of Australia on 12 January 1836 reminded him of Patagonia, but inland the country improved and he was soon filled with admiration at the bustling city of Sydney. On a journey into the interior he came across a group of cheery aborigines who gave him a display of spear throwing for a shilling, contradicting their usual depiction as "degraded creatures", and he reflected sadly on how their numbers were rapidly decreasing. At a large sheep farm he joined a hunting party and caught his first marsupial, a "potoroo" (rat-kangaroo), making him think that an unbeliever "might exclaim 'Surely two distinct Creators must have been [at] work'." He was then shown the even stranger platypus and was surprised to find that its bill was soft, unlike in preserved specimens, and heard that many colonists believed them to lay eggs like a reptile, a point then the subject of scientific controversy in Britain. Still in Australia, the Beagle visited Hobart, Van Diemens Land, then sailed to King George's Sound in south west Australia, a dismal settlement then being replaced by the Swan River Colony. Here Darwin attended an aboriginal dance, a "most rude barbarous scene" "all moving in hideous harmony" though he liked these "good humoured" aborigines "in such high spirits". The Beagle's departure in a storm was delayed when she ran aground. She was refloated and got on her way.

Keeling Island homewards

On their arrival at Keeling Island in the Indian Ocean on 1 April Darwin found a coconut economy, serving both the inhabitants and the wildlife. They investigated the coral lagoons, and FitzRoy's survey soundings revealed a profile consistent with the theory of atolls that Darwin had developed in Lima. Once again Darwin was a martyr to seasickness on the voyage to Mauritius, where he was impressed by the civilisation of the French colony and toured the island, partly on an elephant.

The Beagle reached the Cape of Good Hope on 31 May. In Cape Town Darwin received correspondence from his sister telling him that ten of his letters on South American geology had been edited by Henslow and printed for private distribution, establishing his reputation. After a week there Darwin and FitzRoy visited the noted astronomer Sir John Herschel who was making observations as well as taking a keen interest in geology, corresponding with Lyell on the formation of continents and on the mystery of how new species of life-forms arrived, subjects he may have discussed with them over dinner. In Cape Town, FitzRoy was requested to contribute a piece to the South African Christian Recorder and after they had set to sea on 18 June he wrote an open letter on the Moral State of Tahiti incorporating extracts from Darwin's diary and defending the reputation of missionaries. This was given to a passing ship which took it to Cape Town to become FitzRoy's (and Darwin's) first published work.

At some stage when organising his notes between then and August, Darwin wrote in his Ornithological Notes about the Galapagos mockingbird Mimus thenca that:

    The specimens from Chatham & Albemarle Isd appear to be the same; but the other two are different. In each Isld each kind is exclusively found: habits of all are indistinguishable. When I recollect the fact that [from] the form of the body, shape of scales & general size, the Spaniards can at once pronounce from which Island any Tortoise may have been brought. When I see these Islands in sight of each other, & possessed of but a scanty stock of animals, tenanted by these birds but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties. The only fact of a similar kind of which I am aware is the constant asserted difference between the wolf-like Fox of East & West Falkland Islds. If there is the slightest foundation for these remarks the zoology of Archipelagoes will be well worth examining; for such facts (would) undermine the stability of Species.

The term "would" before "undermine" had been a cautious addition after writing what is now noted as the first expression of his doubts about species being immutable, which led to him being convinced about the transmutation of species and hence evolution. Though his suspicions about the Falkland Island Fox may have been unsupported, the differences in Gal�pagos tortoises between islands were remembered, and on his return John Gould informed Darwin that the mockingbirds were not just varieties, but distinct species. The idea that varieties are actually incipient species was to be crucial for Darwin's evolutionary ideas.[10]

On 8 July they stopped at St. Helena for six days, and here Darwin noted the prevalence of imported English plants. He examined a band of fossil shells at 2,000 ft (600 m) which had been assumed to indicate that St. Helena had risen from the ocean in recent times, but Darwin was able to disprove this by identifying them as ancient land shells of an extinct species.

The Beagle reached Ascension Island on 19 July, and Darwin saw the red volcanic cones of this "cinder" in the ocean. On 23 July they set off again with most of the crew hoping to reach home soon, but FitzRoy wanted to ensure the accuracy of his longitude measurements and so took the ship across the Atlantic back to Bahia in Brazil to take check readings. Darwin took this opportunity to revisit the jungle for five days, but the return trip was delayed for a further 11 days when weather forced the Beagle to shelter further up the coast. The Beagle departed for home on 17 August, and after a stormy passage including a stop for supplies at the Azores, the Beagle finally reached Falmouth, Cornwall, England on 2 October 1836.

Return

Upon his return, Darwin was quick to take the coach home, arriving late at night on 4 October 1836 at The Mount House, the family home in Shrewsbury, Shropshire. Darwin reportedly headed straight to bed and greeted his family at breakfast. After ten days of catching up with family he went on to Cambridge and sought Henslow's advice on organising the description and cataloguing of his collections.

Darwin's father gave him an allowance that enabled him to put aside other careers, and as a scientific celebrity with a reputation established by his fossils and Henslow's publication of his letters on South American geology, he toured London's society institutions. By this time he was part of the "scientific establishment", collaborating with expert naturalists to describe his specimens, and working on ideas he had been developing during the voyage. Charles Lyell gave him enthusiastic backing. In December 1836, Darwin presented a talk to the Cambridge Philosophical Society. He wrote a paper proving that Chile, and the South American continent, was slowly rising, which he read to the Geological Society of London on 4 January 1837.

Syms Covington stayed with Darwin as his servant until shortly after Darwin's marriage in January 1837, when he parted on good terms and migrated to Australia.

[scribe]

In biology, evolution is the change in the inherited traits of a population from generation to generation. These traits are the expression of genes that are copied and passed on to offspring during reproduction. Mutations in these genes can produce new or altered traits, resulting in heritable differences (genetic variation) between organisms. New traits can also come from transfer of genes between populations, as in migration, or between species, in horizontal gene transfer. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through natural selection or randomly through genetic drift.

Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become more rare. This occurs because organisms with advantageous traits pass on more copies of these heritable traits to the next generation.[1][2] Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.[3] In contrast, genetic drift produces random changes in the frequency of traits in a population. Genetic drift arises from the role chance plays in whether a given individual will survive and reproduce.

One definition of a species is a group of organisms that can reproduce with one another and produce fertile offspring. However, when a species is separated into populations that are prevented from interbreeding, mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of new species.[4] The similarities between organisms suggest that all known species are descended from a common ancestor (or ancestral gene pool) through this process of gradual divergence.[1]

The theory of evolution by natural selection was proposed roughly simultaneously by both Charles Darwin and Alfred Russel Wallace, and set out in detail in Darwin's 1859 book On the Origin of Species.[5] In the 1930s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis,[6] in which the connection between the units of evolution (genes) and the mechanism of evolution (natural selection) was made. This powerful explanatory and predictive theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth.[7]

References
   1. a b c Futuyma, Douglas J. (2005). Evolution. Sunderland, Massachusetts: Sinauer Associates, Inc. ISBN 0-87893-187-2.
   2. a b Lande R, Arnold SJ (1983). "The measurement of selection on correlated characters". Evolution 37: 1210�26}. DOI:10.2307/2408842.
   3. Ayala FJ (2007). "Darwin's greatest discovery: design without designer". Proc. Natl. Acad. Sci. U.S.A. 104 Suppl 1: 8567�73. PMID 17494753.
   4. (Gould 2002)
   5. a b c Darwin, Charles (1859). On the Origin of Species, 1st, John Murray, p. 1. . Related earlier ideas were acknowledged in Darwin, Charles (1861). On the Origin of Species, 3rd, John Murray, p. xiii.
   6. a b c d Kutschera U, Niklas K (2004). "The modern theory of biological evolution: an expanded synthesis". Naturwissenschaften 91 (6): 255�76. PMID 15241603.
   7. IAP Statement on the Teaching of Evolution. The Interacademy Panel on International Issues (2006). Retrieved on 25 April 2007.�Statement on the Teaching of Evolution. American Association for the Advancement of Science (2006). Retrieved on 25 April 2007.

[Bart]

When the major dating system relies upon circular reasoning (ie geology, very unscientific), I must  question all data that follows, no matter how scientific the data.

Bart
[/color]

Fossil Sparks, New Finds Ignite Controversy Over Ape and Human Evolution

Bruce Bower

   Fifty years ago, British anatomist Wilfrid Le Gros Clark explained in a lecture why evolutionary scientists argue so vehemently about how ancient apelike and humanlike creatures eventually gave way to modern humans. "Every fossil relic which appears to throw light on connecting links in man's ancestry always has, and always will, arouse controversy," he stated, "and it is right that this should be so, for it is very true that the sparks of controversy often illuminate the way to truth."

DENTAL PLAN. Three Chororapithecus teeth (top) are shown aligned with the corresponding teeth of a female gorilla.
Suwa

   Le Gros Clark was no stranger to wringing the truth out of bits of fossilized skeleton. In 1953, he assisted in unmasking the infamous Piltdown hoax. For more than 40 years, researchers had assumed that skull and jaw fragments collected from a British gravel pit came from a previously unknown early human species. The finds actually consisted of an orangutan's lower jaw and a modern man's skull.

   But Le Gros Clark knew that genuine fossil discoveries ignite brighter sparks of controversy than any cranial con job ever could. Given limited evidence about long-gone populations of our predecessors, researchers devise competing evolutionary scenarios that are often difficult to disprove and that can easily accommodate whatever ancient bones turn up next.

   Scientific reactions to the latest fossil finds and analyses underscore Le Gros Clark's point. Consider a handful of 10-million-year-old teeth recently unearthed in Ethiopia and attributed by their discoverers to a direct ancestor or close relative of the gorilla. If the scientists are right, ancient gorillas initially diverged from human ancestors more than 10 million years ago, several million years before DNA-based analyses date the split. However, some researchers regard the ancient teeth as remnants of an extinct ape that probably bore no relation at all to gorillas.

   Further along evolution's path lie new fossil finds in Kenya that tell a disputed story about the emergence of direct human ancestors. Scientists who uncovered the ancient braincase and partial upper jaw say that this evidence, combined with prior fossils, indicates that two Homo species lived simultaneously in eastern Africa from about 1.9 million to 1.4 million years ago. In this scenario, one species died out and the other led to modern humans. But one prominent anthropologist rejects that conclusion, placing both new fossils in a single species that preceded Homo sapiens.

   Finally, a research team recently argued that its new analysis of fossil teeth from sites in and beyond Africa supports the controversial notion that human ancestors trekked from Africa into Asia well before 2 million years ago and then colonized Europe from Asia. Critics of the work say that more fossil evidence is needed to overturn this team's conclusion that Africans migrated into Asia no more than 1.8 million years ago and eventually settled Europe as well.

   "It's possible that hominids [the fossil ancestors of people] left Africa as early as 2 million years ago," says anthropologist Tim White of the University of California, Berkeley, "but it's hard to untangle the geographic patterns of their movements."

Pieces of Ape

   In February 2006, a field assistant working with fossil hunters in Ethiopia's Chorora Formation, a series of sediment layers dated at between 10 million and 11 million years old, found an ape's canine tooth. One year later, the researchers returned to the site and found eight more teeth from the same ancient-ape species, which they dubbed Chororapithecus abyssinicus.

SHRUNKEN HEAD? A small, newly discovered Homo erectus cranium, shown from above, contrasts with a large, previously unearthed skull from the same species.
Spoor and J. Reader/National Museums of Kenya

   Anthropologist Gen Suwa of the University of Tokyo and his coworkers see signs of gorilla ancestry in the fossils. Computerized tomography scans show that the gorilla-size teeth contain thick enamel suitable for shredding foods such as stems and leaves, the scientists report in the Aug. 23 Nature. Modern gorillas display slightly thinner dental enamel but eat the same types of vegetation. Crests on the chewing surfaces of the ancient teeth look like early versions of the more-pronounced crests in present-day gorillas, the researchers note.

   Chororapithecus represents either an early, direct ancestor of gorillas or a dead-end primate that happened to evolve gorillalike teeth, in their view.

   Precious few African-ape fossils from between 12 million and 7 million years ago have been recovered. Some scientists have speculated that the line of ancestral apes from which chimpanzees, gorillas, and people emerged came from Asia and Europe and later spread into Africa. Chororapithecus suggests instead that this evolutionary process began in Africa, Suwa's team holds.

   Moreover, the new finds indicate that an evolutionary split of direct gorilla ancestors from apelike precursors of people occurred more than 10 million years ago, the investigators say. In contrast, analyses of modern human and ape DNA place that split at about 8 million years ago.

   DNA studies also estimate that the split of chimp from human ancestors happened 6 million years ago, and that the human-orangutan split occurred about 14 million years ago.

   Given the age of Chororapithecus, Suwa's group puts the human-orangutan split at roughly 20 million years ago, the human-gorilla split at about 12 million years ago, and the human-chimp split at 9 million years ago.

   Suwa's conclusion that the Ethiopian fossils come from either a gorilla ancestor or an evolutionary cousin of ancient gorillas makes sense, remarks anthropologist Michel Brunet of the University of Poitiers in France. The teeth of the oldest known hominid, which lived about 7 million years ago, look "completely different" from those of Chororapithecus, Brunet says.

   The French researcher's team unearthed the ancient hominid's nearly complete skull in central Africa (SN: 7/13/02, p. 19). Many investigators accept that specimen as the oldest fossil ancestor of people, but others regard it as an ancient ape.

   Chororapithecus also has a disputed identity. The new find could easily have come from an ancient ape that had nothing to do with gorilla ancestors but evolved one or a few gorillalike dental traits on its own, says anatomist John Kelley of the University of Illinois at Chicago. The Ethiopian fossils have virtually nothing in common with the teeth of modern gorillas, aside from crests on their chewing surfaces that would have aided in grinding up vegetation, Kelley asserts.

   Suwa will keep looking for more pieces of ape. "There is no way to predict future finds at Chorora," he says.

Separate paths

   Scientists have long regarded Homo habilis and Homo erectus as the first two links in an evolutionary chain that ended with the appearance of modern humans. In this view, the relatively small-brained H. habilis evolved about 2 million years ago from earlier African hominids. It evolved into the larger-brained H. erectus by around 1.6 million years ago.

   New fossil finds challenge that portrait of our distant ancestors, say anatomist Fred Spoor of University College London and his coworkers. H. habilis and H. erectus evolved independently of each other, Spoor's team contends. Rather than one species giving way to the next, both species lived simultaneously in eastern Africa for roughly 500,000 years, the scientists report in the Aug. 9 Nature.

   That conclusion rests on an analysis of two fossils unearthed in Kenya in 2000. One fossil consists of a piece of upper jaw. Chemical studies of volcanic-ash layers above and below the find place its age at 1.44 million years.

   The jaw contains six teeth, running from a canine tooth in front to a wisdom tooth in back. The size and shape of the teeth, as well as evidence that the roof of the mouth was wide and shallow, align the fossil with H. habilis, according to Spoor's group.

   The second fossil consists of a small braincase with an estimated age of 1.55 million years. This specimen bears several traits unique to H. erectus, including a bony ridge running over the top of the head and a delicate jaw joint.

   Since the two species coexisted in the same region for such a long time, each must have had separate origins between 3 million and 2 million years ago, the researchers contend. Few hominid fossils have turned up from that period.

   H. sapiens apparently evolved from H. erectus, possibly via an intermediate species, in Spoor's view. H. habilis was a sister species of H. erectus and eventually hit an evolutionary dead-end.

   The newly discovered fossil brain case belonged to the smallest known H. erectus individual. The find thus indicates a size range for H. erectus fossils of eastern Africa that almost equals that for modern gorillas. The gorilla pattern reflects males' large size advantage over females, a condition that may also have applied to male and female H. erectus, says study coauthor Susan C. Ant�n of New York University.

   If so, then H. erectus males may have mated with multiple females and tried to monopolize access to them, as male gorillas do.

   Such conclusions don't sit well with Berkeley's White. He classifies both new fossil finds as H. erectus and as valuable additions to the fossil record, but hardly the stuff of major evolutionary revisions.

   White sees Spoor's paper as part of an ongoing scientific movement to increase the number of species and evolutionary branches on the hominid family tree. In contrast, White argues that early hominids usually evolved from one species to the next, without branching into multiple species (SN: 4/15/06, p. 227).

   "What's interesting is how few hominid lineages there were," White says. He regards early hominids, or australopithecines, as one such lineage that evolved into a second, the Homo lineage, more than 2 million years ago. A group of species called robust australopithecines, which died out 1.2 million years ago, qualifies as a third hominid lineage, in his view.


Eastern origins

   Teeth sometimes tell contested evolutionary tales. That adage applies to a new analysis of hominid teeth conducted by researchers who have found 400,000-year-old skeletons of Neandertal ancestors in Spain and the 1.77-million-year-old remains of an early Homo species in central Asia (SN: 9/22/07, p. 179). The scientists suspect that, perhaps 2 million to 3 million years ago, Asian hominids began to move west, exerting a huge impact on the evolution of Neandertals and other Homo species in western Asia and Europe.

   That suggestion contrasts with the traditional view that hominids left Africa around 1.8 million years ago and evolved into species such as Neandertals after reaching Europe and other locales. Asian hominids of the time evolved separately and eventually died out, according to this perspective.

   A team led by Maria Martin�n-Torres of the National Center of Human Evolution Studies in Burgos, Spain, has examined 51 anatomical traits on more than 5,000 hominid teeth. Fossils came from African australopithecines and from African, Asian, and European Homo species, including H. sapiens.

   Up to the appearance of Neandertals in Europe around 130,000 years ago and modern H. sapiens in Africa 200,000 years ago, dental features fall into two geographic categories, the researchers report in the Aug. 14 Proceedings of the National Academy of Sciences. African teeth display one suite of characteristics, while Asian and European teeth share a different dental signature.

   Asian hominids apparently made a substantial genetic contribution to the evolution of later European species, the scientists say.

   However, anthropologist David Frayer of the University of Kansas in Lawrence says that Martin�n-Torres and her coworkers need larger numbers of fossils, especially of H. sapiens, to make their case. Moreover, the researchers didn't consider several dental traits that differ between Neandertals and Asian hominids, he argues.

   To paraphrase Le Gros Clark, let the sparks of controversy fly. They may burn brightly enough to illuminate a bit of evolutionary truth.

Source

[Administration]

So like archaeology, where proof is rare and all is a balance of probabilities.

In the 1980s, I had a guest stay with me for a week, who was a professor of biology. I was bold enough to make some observations in support of evolution and he replied with a list of human biological features which were impossible according to evolutionary logic.

Here is a question which always pops into mind when the subject arises:

Among all the millions of extant species observed by humanity over thousands of years, what examples are there of observed evolution from one species to another?

Since the above conversation, I have had the pleasure of working with some of the top scientists in Britain and Europe and have oft posed that question to them, yet have never received a positive reply.