Peter Simon Pallas
Peter Simon Pallas FRS FRSE was a Prussian zoologist and botanist who worked in Russia. Pallas was born in the son of Professor of Surgery Simon Pallas, he studied with private tutors and took an interest in natural history attending the University of Halle and the University of Göttingen. In 1760, he moved to the University of Leiden and passed his doctor's degree at the age of 19. Pallas travelled throughout the Netherlands and to London, improving his medical and surgical knowledge, he settled at The Hague, his new system of animal classification was praised by Georges Cuvier. Pallas wrote Miscellanea Zoologica, which included descriptions of several vertebrates new to science which he had discovered in the Dutch museum collections. A planned voyage to southern Africa and the East Indies fell through when his father recalled him to Berlin. There, he began work on his Spicilegia Zoologica. In 1767, Pallas was invited by Catherine II of Russia to become a professor at the St Petersburg Academy of Sciences and, between 1768 and 1774, he led an expedition to central Russian provinces, Urals, West Siberia and Transbaikal, collecting natural history specimens for the academy.
He explored the Caspian Sea, the Ural and Altai Mountains and the upper Amur River, reaching as far eastward as Lake Baikal. The regular reports which Pallas sent to St Petersburg were collected and published as Reise durch verschiedene Provinzen des Russischen Reichs, they covered a wide range of topics, including geology and mineralogy, reports on the native peoples and their religions, descriptions of new plants and animals. In 1776, Pallas was elected a foreign member of the Royal Swedish Academy of Sciences. Pallas settled in St Petersburg, becoming a favourite of Catherine II and teaching natural history to the Grand Dukes Alexander and Constantine, he was provided with the plants collected by other naturalists to compile the Flora Rossica, a Russian flora, started work on his Zoographica Rosso-Asiatica, a zoography of Russia and Asia. He published an account of Johann Anton Güldenstädt's travels in the Caucasus; the Empress bought Pallas's large natural history collection for 2,000 rubles, 500 more than his asking price, allowed him to keep them for life.
During this period, Pallas helped plan the Mulovsky expedition, cancelled in October 1787. Between 1793 and 1794, Pallas led a second expedition to southern Russia, visiting the Crimea and the Black Sea, he was accompanied by his daughter and his new wife, an artist, a military escort. In February 1793, they travelled to Saratov and downriver to Tsaritsyn, they explored the country to the east, in August travelled along the banks of the Caspian Sea and into the Caucasus Mountains. In September, they travelled to the Crimea. Pallas spent early 1794 exploring to the southeast, in July travelled up the valley of the Dnieper, arriving back in St Petersburg in September. Pallas gave his account of the journey in his P. S. Pallas Bemerkungen auf einer Reise in die Südlichen Statthalterschaften des Russischen Reichs. Catherine II gave him a large estate at Simferopol, where Pallas lived until the death of his second wife in 1810, he was granted permission to leave Russia by Emperor Alexander, returned to Berlin, where he died in the following year.
His grave is preserved in the Protestant Friedhof I der Jerusalems- und Neuen Kirchengemeinde in Berlin-Kreuzberg, south of Hallesches Tor. In 1809 he became associate member of the Royal Institute of the Netherlands. In 1772, Pallas was shown a 680-kg lump of metal, found near Krasnoyarsk. Pallas arranged. Subsequent analysis of the metal showed it to be a new type of stony-iron meteorite; this new type of meteorite was called pallasite after him. Several animals were described by Pallas, his surname is included in their common names, including: Pallas' glass lizard, Pallas' viper, Pallas's cat, Pallas's long-tongued bat, Pallas's tube-nosed bat, Pallas's squirrel, Pallas's leaf warbler, Pallas's cormorant, Pallas's fish-eagle, Pallas's gull, Pallas's sandgrouse, Pallas's rosefinch, Pallas's grasshopper warbler, he is honoured in the scientific names of animals described by others, including: the Dagestani tortoise, Pallas's pika, Pallas's reed bunting, the Pacific herring. Streets in Berlin and Castrop-Rauxel are named Pallasstraße.
Pallasovka, a city in Volgograd Oblast, is named after him, his monument stands there. An asteroid is named after him: 21087 Petsimpallas. A Belgian astronomer, Eric Elst chose the name "Sarapul 26851" for an asteroid because in Pallas' writings, he mentioned his liking of the city of Sarapul, Russia. Dissertatio inauguralis. Elenchus zoophytorum, sistens generum adumbrationes generaliores et specierum cognitarum succinctas descriptiones, cum selectis auctorum synonymis. Miscellanea zoologica, quibus novæ imprimis atque obscuræ animalum species describuntur et observationibus iconibusque illustrantur. Spicilegia zoologica. Lyst der Plant-Dieren, bevattende de algemeene schetzen der geslachten en korte beschryvingen der bekende zoorten (Utrecht: van Paddenburg & van S
Kuwait the State of Kuwait, is a country in Western Asia. Situated in the northern edge of Eastern Arabia at the tip of the Persian Gulf, it shares borders with Iraq and Saudi Arabia; as of 2016, Kuwait has a population of 4.5 million people: 1.3 million are Kuwaitis and 3.2 million are expatriates. Expatriates account for 70% of the population. Oil reserves were discovered in commercial quantities in 1938. From 1946 to 1982, the country underwent large-scale modernization. In the 1980s, Kuwait experienced a period of geopolitical instability and an economic crisis following the stock market crash. In 1990, Kuwait was invaded, annexed, by Saddam's Iraq; the Iraqi occupation of Kuwait came to an end in 1991 after military intervention by a military coalition led by the United States. Kuwait is a major non-NATO ally of the United States, it is a major ally of ASEAN, while maintaining a strong relationship with China. Kuwait is a constitutional sovereign state with a semi-democratic political system.
Kuwait has a high-income economy backed by the world's sixth largest oil reserves. The Kuwaiti dinar is the highest valued currency in the world. According to the World Bank, the country has the fourth highest per capita income; the Constitution was promulgated in 1962. Kuwait is home to the largest opera house in the Middle East; the Kuwait National Cultural District is a member of the Global Cultural Districts Network. In 1613, the town of Kuwait was founded in modern-day Kuwait City. Administratively, it was a sheikhdom, ruled by local sheikhs. In 1716, the Bani Utub settled in Kuwait, which at this time was inhabited by a few fishermen and functioned as a fishing village. In the eighteenth century, Kuwait prospered and became the principal commercial center for the transit of goods between India, Muscat and Arabia. By the mid 1700s, Kuwait had established itself as the major trading route from the Persian Gulf to Aleppo. During the Persian siege of Basra in 1775–79, Iraqi merchants took refuge in Kuwait and were instrumental in the expansion of Kuwait's boat-building and trading activities.
As a result, Kuwait's maritime commerce boomed, as the Indian trade routes with Baghdad, Aleppo and Constantinople were diverted to Kuwait during this time. The East India Company was diverted to Kuwait in 1792; the East India Company secured the sea routes between Kuwait and the east coasts of Africa. After the Persians withdrew from Basra in 1779, Kuwait continued to attract trade away from Basra. Kuwait was the center of boat building in the Persian Gulf region. During the late eighteenth and nineteenth centuries, vessels made in Kuwait carried the bulk of trade between the ports of India, East Africa and the Red Sea. Kuwaiti ships were renowned throughout the Indian Ocean. Regional geopolitical turbulence helped foster economic prosperity in Kuwait in the second half of the 18th century; the biggest catalyst for much of Kuwait becoming prosperous was due to Basra's instability in the late 18th century. In the late 18th century, Kuwait functioned as a haven for Basra's merchants, who were fleeing Ottoman government persecution.
Kuwaitis developed a reputation as the best sailors in the Persian Gulf. In the 1890s, Kuwait began to feel threatened by the Ottoman empire. In a bid to address its security issues, the ruler, Sheikh Mubarak Al Sabah signed an agreement with the British government in India, subsequently known as the Anglo-Kuwaiti Agreement of 1899 and became a British protectorate; the Sheikhdom of Kuwait remained a British protectorate from 1899. Following the Kuwait–Najd War of 1919–20, Ibn Saud imposed a trade blockade against Kuwait from the years 1923 until 1937; the goal of the Saudi economic and military attacks on Kuwait was to annex as much of Kuwait's territory as possible. At the Uqair conference in 1922, the boundaries of Kuwait and Najd were set. Ibn Saud persuaded Sir Percy Cox to give him two-thirds of Kuwait's territory. More than half of Kuwait was lost due to Uqair. After the Uqair conference, Kuwait was still subjected to a Saudi economic blockade and intermittent Saudi raiding; the Great Depression harmed Kuwait's economy.
International trading was one of Kuwait's main sources of income before oil. Kuwaiti merchants were intermediary merchants; as a result of the decline of European demand for goods from India and Africa, Kuwait's economy suffered. The decline in international trade resulted in an increase in gold smuggling by Kuwaiti ships to India; some Kuwaiti merchant families became rich from this smuggling. Kuwait's pearl industry collapsed as a result of the worldwide economic depression. At its height, Kuwait's pearl industry had led the world's luxury market sending out between 750 and 800 ships to meet the European elite's desire for pearls. During the economic depression, luxuries like pearls were in little demand; the Japanese invention of cultured pearls contributed to the collapse of Kuwait's pearl industry. Historian Hanna Batatu explains how the British threatened to take the Kurdish area and Mosul out of Iraq provided that King Faisal granted Britain control of the oil in the region. In 1938 the Kuwaiti Legislative Council unanimously approved a request for Kuwait’s reintegration with Iraq.
A year an armed uprising which had raised the integration banner as its objective was put down by the British. With the end of the world war, increasing need for oil across the world, Kuwait experienced a period of prosperity driven by oil and its liberal atmosphere; the period
Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, the only bird family in the order Phoenicopteriformes. Four flamingo species are distributed throughout the Americas, including the Caribbean, two species are native to Africa and Europe; the name "flamingo" comes from Portuguese or Spanish flamengo, "flame-colored", in turn coming from Provençal flamenc from flama "flame" and Germanic-like suffix -ing, with a possible influence of words like "Fleming". A similar etymology has the Latinate Greek term phoenicopterus "blood red-feathered". Traditionally, the long-legged Ciconiiformes a paraphyletic assemblage, have been considered the flamingos' closest relatives and the family was included in the order; the ibises and spoonbills of the Threskiornithidae were considered their closest relatives within this order. Earlier genetic studies, such as those of Charles Sibley and colleagues supported this relationship. Relationships to the waterfowl were considered as well as flamingos are parasitized by feather lice of the genus Anaticola, which are otherwise found on ducks and geese.
The peculiar presbyornithids were used to argue for a close relationship between flamingos and waders. A 2002 paper concluded they are waterfowl, but a 2014 comprehensive study of bird orders found that flamingos and grebes are not waterfowl, but rather are part of Columbea along with doves and mesites. Living flamingoes. Six extant flamingo species are recognized by most sources, were placed in one genus – Phoenicopterus; as a result of a 2014 publication, the family was reclassified into three genera. Prehistoric species of flamingo: Phoenicopterus floridanus Brodkorb 1953 Phoenicopterus stocki Phoenicopterus siamensis Cheneval et al. 1991 Phoenicopterus gracilis Miller 1963 Phoenicopterus copei Phoenicopterus minutus Phoenicopterus croizeti Phoenicopterus aethiopicus Phoenicopterus eyrensis Phoenicopterus novaehollandiae Recent molecular studies have suggested a relation with grebes, while morphological evidence strongly supports a relationship between flamingos and grebes. They hold at least 11 morphological traits in common.
Many of these characteristics have been identified on flamingos, but not on grebes. The fossil palaelodids can be considered evolutionarily, ecologically, intermediate between flamingos and grebes. For the grebe-flamingo clade, the taxon Mirandornithes has been proposed. Alternatively, they could be placed with Phoenocopteriformes taking priority. Flamingos stand on one leg while the other is tucked beneath their bodies; the reason for this behaviour is not understood. One theory is that standing on one leg allows the birds to conserve more body heat, given that they spend a significant amount of time wading in cold water. However, the behaviour takes place in warm water and is observed in birds that do not stand in water. An alternative theory is that standing on one leg reduces the energy expenditure for producing muscular effort to stand and balance on one leg. A study on cadavers showed that the one-legged pose could be held without any muscle activity, while living flamingos demonstrate less body sway in a one-legged posture.
As well as standing in the water, flamingos may stamp their webbed feet in the mud to stir up food from the bottom. Flamingos are capable flyers, flamingos in captivity require wing clipping to prevent escape. Young flamingos hatch with greyish-red plumage, but adults range from light pink to bright red due to aqueous bacteria and beta-carotene obtained from their food supply. A well-fed, healthy flamingo is thus a more desirable mate. Captive flamingos are a notable exception; the greater flamingo is the tallest of the 6 different species of flamingos, standing at 3.9 to 4.7 feet with a weight up to 7.7 pounds, the shortest flamingo species has a height of 2.6 feet and weighs 5.5 pounds. Flamingos can have a wingspan as small as 37 inches to as big as 59 inches. Flamingos filter-feed on brine shrimp and blue-green algae as well as larva, small insects and crustaceans making them omnivores, their bills are specially adapted to separate mud and silt from the food they eat, are uniquely used upside-down.
The filtering of food items is assisted by hairy structures called lamellae, which line the mandibles, the large, rough-surfaced tongue. The pink or reddish color of flamingos comes from carotenoids in their diet of animal and plant plankton. American flamingos are a brighter red color because of the beta carotene availability in their food while the lesser flamingos are a paler pink due to ingesting a smaller amount of this pigment; these carotenoids are broken down into pigments by liver enzymes. The source of this varies by species, affects the color saturation. Flamingos whose sole diet is blue-green algae are darker than those that get it second-hand by eating animals that have digested blue-green algae). Flamingos are social birds.
Gujarat is a state on the western coast of India with a coastline of 1,600 km – most of which lies on the Kathiawar peninsula – and a population in excess of 60 million. It is the ninth largest state by population. Gujarat is bordered by Rajasthan to the northeast and Diu to the south and Nagar Haveli and Maharashtra to the southeast, Madhya Pradesh to the east, the Arabian Sea and the Pakistani province of Sindh to the west, its capital city is Gandhinagar. The Gujarati-speaking people of India are indigenous to the state; the economy of Gujarat is the fifth-largest state economy in India with ₹14.96 lakh crore in gross domestic product and a per capita GDP of ₹157,000. The state encompasses some sites of the ancient Indus Valley Civilisation, such as Lothal and Gola Dhoro. Lothal is believed to be one of the world's first seaports. Gujarat's coastal cities, chiefly Bharuch and Khambhat, served as ports and trading centers in the Maurya and Gupta empires, during the succession of royal Saka dynasties from the Western Satraps era.
Along with Bihar and Nagaland, Gujarat is one of the three Indian states to prohibit the sale of alcohol. Present-day Gujarat is derived from Sanskrit term Gurjaradesa, meaning the land of the Gurjaras who ruled Gujarat in the 8th and 9th centuries AD. Parts of modern Rajasthan and Gujarat have been known as Gurjaratra or Gurjarabhumi for centuries before the Mughal period. Gujarat was one of the main central areas of the Indus Valley Civilisation, it contains ancient metropolitan cities from the Indus Valley such as Lothal and Gola Dhoro. The ancient city of Lothal was; the ancient city of Dholavira is one of the largest and most prominent archaeological sites in India, belonging to the Indus Valley Civilisation. The most recent discovery was Gola Dhoro. Altogether, about 50 Indus Valley settlement ruins have been discovered in Gujarat; the ancient history of Gujarat was enriched by the commercial activities of its inhabitants. There is clear historical evidence of trade and commerce ties with Egypt and Sumer in the Persian Gulf during the time period of 1000 to 750 BC.
There was a succession of Hindu and Buddhist states such as the Mauryan Dynasty, Western Satraps, Satavahana dynasty, Gupta Empire, Chalukya dynasty, Rashtrakuta Empire, Pala Empire and Gurjara-Pratihara Empire, as well as local dynasties such as the Maitrakas and the Chaulukyas. The early history of Gujarat reflects the imperial grandeur of Chandragupta Maurya who conquered a number of earlier states in what is now Gujarat. Pushyagupta, a Vaishya, was appointed the governor of Saurashtra by the Mauryan regime, he built a dam on the Sudarshan lake. Emperor Ashoka, the grandson of Chandragupta Maurya, not only ordered engraving of his edicts on the rock at Junagadh but asked Governor Tusherpha to cut canals from the lake where an earlier Mauryan governor had built a dam. Between the decline of Mauryan power and Saurashtra coming under the sway of the Samprati Mauryas of Ujjain, there was an Indo-Greek defeat in Gujarat of Demetrius. In 16th century manuscripts, there is an apocryphal story of a merchant of King Gondaphares landing in Gujarat with Apostle Thomas.
The incident of the cup-bearer torn apart by a lion might indicate that the port city described is in Gujarat. For nearly 300 years from the start of the 1st century AD, Saka rulers played a prominent part in Gujarat's history; the weather-beaten rock at Junagadh gives a glimpse of the ruler Rudradaman I of the Saka satraps known as Western Satraps, or Kshatraps. Mahakshatrap Rudradaman I founded the Kardamaka dynasty which ruled from Anupa on the banks of the Narmada up to the Aparanta region which bordered Punjab. In Gujarat, several battles were fought between the south Indian Satavahana dynasty and the Western Satraps; the greatest and the mightiest ruler of the Satavahana Dynasty was Gautamiputra Satakarni who defeated the Western Satraps and conquered some parts of Gujarat in the 2nd century AD. The Kshatrapa dynasty was replaced by the Gupta Empire with the conquest of Gujarat by Chandragupta Vikramaditya. Vikramaditya's successor Skandagupta left an inscription on a rock at Junagadh which gives details of the governor's repairs to the embankment surrounding Sudarshan lake after it was damaged by floods.
The Anarta and Saurashtra regions were both parts of the Gupta empire. Towards the middle of the 5th century, the Gupta empire went into decline. Senapati Bhatarka, the Maitraka general of the Guptas, took advantage of the situation and in 470 he set up what came to be known as the Maitraka state, he shifted his capital from Giringer near Bhavnagar, on Saurashtra's east coast. The Maitrakas of Vallabhi became powerful with their rule prevailing over large parts of Gujarat and adjoining Malwa. A university was set up by the Maitrakas, which came to be known far and wide for its scholastic pursuits and was compared with the noted Nalanda University, it was during the rule of Dhruvasena Maitrak that Chinese philosopher-traveler Xuanzang/ I Tsing visited in 640 along the Silk Road. Gujarat was known to the ancient Greeks and was familiar with other Western centers of civilization through the end of the European Middle Ages; the oldest written record of Gujarat's 2,000-year maritime history is documented in a Greek book titled The Periplus of the Erythraean Sea: Travel and Trade in the Indian Ocean by a Merchant of the First Century.
In the early 8th century, the Arabs of the Umayyad Caliphate established an empire in the name of the rising religion of Islam, which stretched
France the French Republic, is a country whose territory consists of metropolitan France in Western Europe and several overseas regions and territories. The metropolitan area of France extends from the Mediterranean Sea to the English Channel and the North Sea, from the Rhine to the Atlantic Ocean, it is bordered by Belgium and Germany to the northeast and Italy to the east, Andorra and Spain to the south. The overseas territories include French Guiana in South America and several islands in the Atlantic and Indian oceans; the country's 18 integral regions span a combined area of 643,801 square kilometres and a total population of 67.3 million. France, a sovereign state, is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre. Other major urban areas include Lyon, Toulouse, Bordeaux and Nice. During the Iron Age, what is now metropolitan France was inhabited by a Celtic people. Rome annexed the area in 51 BC, holding it until the arrival of Germanic Franks in 476, who formed the Kingdom of Francia.
The Treaty of Verdun of 843 partitioned Francia into Middle Francia and West Francia. West Francia which became the Kingdom of France in 987 emerged as a major European power in the Late Middle Ages following its victory in the Hundred Years' War. During the Renaissance, French culture flourished and a global colonial empire was established, which by the 20th century would become the second largest in the world; the 16th century was dominated by religious civil wars between Protestants. France became Europe's dominant cultural and military power in the 17th century under Louis XIV. In the late 18th century, the French Revolution overthrew the absolute monarchy, established one of modern history's earliest republics, saw the drafting of the Declaration of the Rights of Man and of the Citizen, which expresses the nation's ideals to this day. In the 19th century, Napoleon established the First French Empire, his subsequent Napoleonic Wars shaped the course of continental Europe. Following the collapse of the Empire, France endured a tumultuous succession of governments culminating with the establishment of the French Third Republic in 1870.
France was a major participant in World War I, from which it emerged victorious, was one of the Allies in World War II, but came under occupation by the Axis powers in 1940. Following liberation in 1944, a Fourth Republic was established and dissolved in the course of the Algerian War; the Fifth Republic, led by Charles de Gaulle, remains today. Algeria and nearly all the other colonies became independent in the 1960s and retained close economic and military connections with France. France has long been a global centre of art and philosophy, it hosts the world's fourth-largest number of UNESCO World Heritage Sites and is the leading tourist destination, receiving around 83 million foreign visitors annually. France is a developed country with the world's sixth-largest economy by nominal GDP, tenth-largest by purchasing power parity. In terms of aggregate household wealth, it ranks fourth in the world. France performs well in international rankings of education, health care, life expectancy, human development.
France is considered a great power in global affairs, being one of the five permanent members of the United Nations Security Council with the power to veto and an official nuclear-weapon state. It is a leading member state of the European Union and the Eurozone, a member of the Group of 7, North Atlantic Treaty Organization, Organisation for Economic Co-operation and Development, the World Trade Organization, La Francophonie. Applied to the whole Frankish Empire, the name "France" comes from the Latin "Francia", or "country of the Franks". Modern France is still named today "Francia" in Italian and Spanish, "Frankreich" in German and "Frankrijk" in Dutch, all of which have more or less the same historical meaning. There are various theories as to the origin of the name Frank. Following the precedents of Edward Gibbon and Jacob Grimm, the name of the Franks has been linked with the word frank in English, it has been suggested that the meaning of "free" was adopted because, after the conquest of Gaul, only Franks were free of taxation.
Another theory is that it is derived from the Proto-Germanic word frankon, which translates as javelin or lance as the throwing axe of the Franks was known as a francisca. However, it has been determined that these weapons were named because of their use by the Franks, not the other way around; the oldest traces of human life in what is now France date from 1.8 million years ago. Over the ensuing millennia, Humans were confronted by a harsh and variable climate, marked by several glacial eras. Early hominids led a nomadic hunter-gatherer life. France has a large number of decorated caves from the upper Palaeolithic era, including one of the most famous and best preserved, Lascaux. At the end of the last glacial period, the climate became milder. After strong demographic and agricultural development between the 4th and 3rd millennia, metallurgy appeared at the end of the 3rd millennium working gold and bronze, iron. France has numerous megalithic sites from the Neolithic period, including the exceptiona
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
Feathers are epidermal growths that form the distinctive outer covering, or plumage, on birds, other extinct species of dinosaurs, pterosaurs. They are considered the most complex integumentary structures found in vertebrates and a premier example of a complex evolutionary novelty, they are among the characteristics. Although feathers cover most of the bird's bodies, they arise only from certain well-defined tracts on the skin, they aid in flight, thermal insulation, waterproofing. In addition, coloration helps in protection. Plumology is the name for the science, associated with the study of feathers. Feathers are among the most complex integumentary appendages found in vertebrates and are formed in tiny follicles in the epidermis, or outer skin layer, that produce keratin proteins; the β-keratins in feathers and claws — and the claws and shells of reptiles — are composed of protein strands hydrogen-bonded into β-pleated sheets, which are further twisted and crosslinked by disulfide bridges into structures tougher than the α-keratins of mammalian hair and hoof.
The exact signals that induce the growth of feathers on the skin are not known, but it has been found that the transcription factor cDermo-1 induces the growth of feathers on skin and scales on the leg. There are two basic types of feather: vaned feathers which cover the exterior of the body, down feathers which are underneath the vaned feathers; the pennaceous feathers are vaned feathers. Called contour feathers, pennaceous feathers arise from tracts and cover the entire body. A third rarer type of feather, the filoplume, is hairlike and are associated with contour feathers and are entirely hidden by them, with one or two filoplumes attached and sprouting from near the same point of the skin as each contour feather, at least on a bird's head and trunk. In some passerines, filoplumes arise exposed beyond the contour feathers on the neck; the remiges, or flight feathers of the wing, rectrices, the flight feathers of the tail are the most important feathers for flight. A typical vaned feather features a main shaft, called the rachis.
Fused to the rachis are a series of branches, or barbs. These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular calamus which inserts into a follicle in the skin; the basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base and a small opening on the side. Hatchling birds of some species have a special kind of natal down feathers which are pushed out when the normal feathers emerge. Flight feathers are stiffened so as to work against the air in the downstroke but yield in other directions, it has been observed that the orientation pattern of β-keratin fibers in the feathers of flying birds differs from that in flightless birds: the fibers are better aligned along the shaft axis direction towards the tip, the lateral walls of rachis region show structure of crossed fibers.
Feathers insulate birds from water and cold temperatures. They may be plucked to line the nest and provide insulation to the eggs and young; the individual feathers in the wings and tail play important roles in controlling flight. Some species have a crest of feathers on their heads. Although feathers are light, a bird's plumage weighs two or three times more than its skeleton, since many bones are hollow and contain air sacs. Color patterns serve as camouflage against predators for birds in their habitats, serve as camouflage for predators looking for a meal; as with fish, the top and bottom colors may be different, in order to provide camouflage during flight. Striking differences in feather patterns and colors are part of the sexual dimorphism of many bird species and are important in selection of mating pairs. In some cases there are differences in the UV reflectivity of feathers across sexes though no differences in color are noted in the visible range; the wing feathers of male club-winged manakins Machaeropterus deliciosus have special structures that are used to produce sounds by stridulation.
Some birds have a supply of powder down feathers which grow continuously, with small particles breaking off from the ends of the barbules. These particles produce a powder that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather conditioner. Powder down has evolved independently in several taxa and can be found in down as well as in pennaceous feathers, they may be scattered in plumage as in the pigeons and parrots or in localized patches on the breast, belly, or flanks, as in herons and frogmouths. Herons use their bill to break the powder down feathers and to spread them, while cockatoos may use their head as a powder puff to apply the powder. Waterproofing can be lost by exposure to emulsifying agents due to human pollution. Feathers can become waterlogged, causing the bird to sink, it is very difficult to clean and rescue birds whose feathers have been fouled by oil spills. The feathers of cormorants soak up water and help to reduce buoyancy, thereby allowing the birds to swim submerged.
Bristles are stiff. Rictal bristles are found around bill, they may serve a similar purpose to e