A desert is a barren area of landscape where little precipitation occurs and living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is semi-arid; this includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which break in pieces. Although rain occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor are further eroded by the wind; this wafts them aloft in sand or dust storms.
Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, the wind sorts sand into uniform deposits; the grains are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones; these areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of seepages from aquifers. Where these are found, oases can occur. Plants and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles and spines to deter herbivory; some annual plants germinate and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture.
Animals need to find enough food and water to survive. Many stay in the shade or underground during the heat of the day, they tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine. Some animals remain in a state of dormancy for long periods, ready to become active again during the rare rainfall, they reproduce while conditions are favorable before returning to dormancy. People have struggled to live in the surrounding semi-arid lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available and oases have provided opportunities for a more settled way of life; the cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Desert farming is possible with the aid of irrigation, the Imperial Valley in California provides an example of how barren land can be made productive by the import of water from an outside source. Many trade routes have been forged across deserts across the Sahara Desert, traditionally were used by caravans of camels carrying salt, gold and other goods.
Large numbers of slaves were taken northwards across the Sahara. Some mineral extraction takes place in deserts, the uninterrupted sunlight gives potential for the capture of large quantities of solar energy. English desert and its Romance cognates all come from the ecclesiastical Latin dēsertum, a participle of dēserere, "to abandon"; the correlation between aridity and sparse population is complex and dynamic, varying by culture and technologies. In English before the 20th century, desert was used in the sense of "unpopulated area", without specific reference to aridity. Phrases such as "desert island" and "Great American Desert", or Shakespeare's "deserts of Bohemia" in previous centuries did not imply sand or aridity. A desert is a region of land, dry because it receives low amounts of precipitation has little coverage by plants, in which streams dry up unless they are supplied by water from outside the area. Deserts receive less than 250 mm of precipitation each year; the potential evapotranspiration may be large but the actual evapotranspiration may be close to zero.
Semideserts are regions which receive between 250 and 500 mm and when clad in grass, these are known as steppes. Deserts have been defined and classified in a number of ways combining total precipitation, number of days on which this falls and humidity, sometimes additional factors. For example, Arizona, receives less than 250 mm of precipitation per year, is recognized as being located in a desert because of its aridity-adapted plants; the North Slope of Alaska's Brooks Range receives less than 250 mm of precipitation per year and is classified as a cold desert. Other regions of the world have cold deserts, including areas of the Himalayas and other high-altitude areas in other parts of the world. Polar deserts cover much of the ice-free
Iran called Persia, the Islamic Republic of Iran, is a country in Western Asia. With over 81 million inhabitants, Iran is the world's 18th most populous country. Comprising a land area of 1,648,195 km2, it is the second largest country in the Middle East and the 17th largest in the world. Iran is bordered to the northwest by Armenia and the Republic of Azerbaijan, to the north by the Caspian Sea, to the northeast by Turkmenistan, to the east by Afghanistan and Pakistan, to the south by the Persian Gulf and the Gulf of Oman, to the west by Turkey and Iraq; the country's central location in Eurasia and Western Asia, its proximity to the Strait of Hormuz, give it geostrategic importance. Tehran is the country's capital and largest city, as well as its leading economic and cultural center. Iran is home to one of the world's oldest civilizations, beginning with the formation of the Elamite kingdoms in the fourth millennium BCE, it was first unified by the Iranian Medes in the seventh century BCE, reaching its greatest territorial size in the sixth century BCE, when Cyrus the Great founded the Achaemenid Empire, which stretched from Eastern Europe to the Indus Valley, becoming one of the largest empires in history.
The Iranian realm fell to Alexander the Great in the fourth century BCE and was divided into several Hellenistic states. An Iranian rebellion culminated in the establishment of the Parthian Empire, succeeded in the third century CE by the Sasanian Empire, a leading world power for the next four centuries. Arab Muslims conquered the empire in the seventh century CE; the Islamization of Iran led to the decline of Zoroastrianism, by the country's dominant religion, Iran's major contributions to art and science spread within the Muslim rule during the Islamic Golden Age. After two centuries, a period of various native Muslim dynasties began, which were conquered by the Seljuq Turks and the Ilkhanate Mongols; the rise of the Safavids in the 15th century led to the reestablishment of a unified Iranian state and national identity, with the country's conversion to Shia Islam marking a turning point in Iranian and Muslim history. Under Nader Shah, Iran was one of the most powerful states in the 18th century, though by the 19th century, a series of conflicts with the Russian Empire led to significant territorial losses.
The Iranian Constitutional Revolution in the early 20th century led to the establishment of a constitutional monarchy and the country's first legislature. A 1953 coup instigated by the United Kingdom and the United States resulted in greater autocracy and growing Western political influence. Subsequent widespread dissatisfaction and unrest against the monarchy led to the 1979 Revolution and the establishment of an Islamic republic, a political system that includes elements of a parliamentary democracy vetted and supervised by a theocracy governed by an autocratic "Supreme Leader". During the 1980s, the country was engaged in a war with Iraq, which lasted for eight years and resulted in a high number of casualties and economic losses for both sides; the sovereign state of Iran is a founding member of the UN, ECO, NAM, OIC, OPEC. It is a major regional and middle power, its large reserves of fossil fuels – which include the world's largest natural gas supply and the fourth largest proven oil reserves – exert considerable influence in international energy security and the world economy.
The country's rich cultural legacy is reflected in part by its 22 UNESCO World Heritage sites, the third largest number in Asia and 11th largest in the world. Iran is a multicultural country comprising numerous ethnic and linguistic groups, the largest being Persians, Azeris and Lurs. Organizations including Amnesty International and Human Rights Watch have criticized Iran's women's rights record; the term Iran derives directly from Middle Persian Ērān, first attested in a third-century inscription at Rustam Relief, with the accompanying Parthian inscription using the term Aryān, in reference to the Iranians. The Middle Iranian ērān and aryān are oblique plural forms of gentilic nouns ēr- and ary-, both deriving from Proto-Iranian *arya-, recognized as a derivative of Proto-Indo-European *ar-yo-, meaning "one who assembles". In the Iranian languages, the gentilic is attested as a self-identifier, included in ancient inscriptions and the literature of the Avesta, remains in other Iranian ethnic names Alan and Iron.
Iran has been referred to as Persia by the West, due to the writings of Greek historians who referred to all of Iran as Persís, meaning "land of the Persians", while Persis itself was one of the provinces of ancient Iran, today defined as Fars. As the most extensive interaction the Ancient Greeks had with any outsider was with the Persians, the term persisted long after the Greco-Persian Wars. In 1935, Reza Shah requested the international community to refer to the country by its native name, effective March 22 that year; as The New York Times explained at the time, "At the suggestion of the Persian Legation in Berlin, the Tehran government, on the Persian New Year, March 21, 1935, substituted Iran for Persia as the official name of the country." Opposition to the name change led to the reversal of the decision, Professor Ehsan Yarshater, editor of Encyclopædia Iranica, propagated a move to use Persia and Iran interchangeably. Today, both Iran and Persia are used in cultural contexts, while Iran remains irreplaceab
Pakistan the Islamic Republic of Pakistan, is a country in South Asia. It is the world’s sixth-most populous country with a population exceeding 212,742,631 people. In area, it is the 33rd-largest country. Pakistan has a 1,046-kilometre coastline along the Arabian Sea and Gulf of Oman in the south and is bordered by India to the east, Afghanistan to the west, Iran to the southwest, China in the far northeast, it is separated narrowly from Tajikistan by Afghanistan's Wakhan Corridor in the northwest, shares a maritime border with Oman. The territory that now constitutes Pakistan was the site of several ancient cultures and intertwined with the history of the broader Indian subcontinent; the ancient history involves the Neolithic site of Mehrgarh and the Bronze Age Indus Valley Civilisation, was home to kingdoms ruled by people of different faiths and cultures, including Hindus, Indo-Greeks, Turco-Mongols and Sikhs. The area has been ruled by numerous empires and dynasties, including the Persian Achaemenid Empire, Alexander III of Macedon, the Seleucid Empire, the Indian Maurya Empire, the Gupta Empire, the Arab Umayyad Caliphate, the Delhi Sultanate, the Mongol Empire, the Mughal Empire, the Afghan Durrani Empire, the Sikh Empire and, most the British Empire.
Pakistan is the only country to have been created in the name of Islam. It is an ethnically and linguistically diverse country, with a diverse geography and wildlife. A dominion, Pakistan adopted a constitution in 1956, becoming an Islamic republic. An ethnic civil war and Indian military intervention in 1971 resulted in the secession of East Pakistan as the new country of Bangladesh. In 1973, Pakistan adopted a new constitution which stipulated that all laws are to conform to the injunctions of Islam as laid down in the Quran and Sunnah. A regional and middle power, Pakistan has the sixth-largest standing armed forces in the world and is a nuclear power as well as a declared nuclear-weapons state, the second in South Asia and the only nation in the Muslim world to have that status. Pakistan has a semi-industrialised economy with a well-integrated agriculture sector and a growing services sector, it is ranked among the emerging and growth-leading economies of the world, is backed by one of the world's largest and fastest-growing middle class.
Pakistan's political history since independence has been characterized by periods of military rule, political instability and conflicts with India. The country continues to face challenging problems, including overpopulation, poverty and corruption. Pakistan is a member of the UN, the Shanghai Cooperation Organisation, the OIC, the Commonwealth of Nations, the SAARC and the Islamic Military Counter Terrorism Coalition; the name Pakistan means "land of the pure" in Urdu and Persian. It alludes to the word pāk meaning pure in Pashto; the suffix ـستان is a Persian word meaning the place of, recalls the synonymous Sanskrit word sthāna स्थान. The name of the country was coined in 1933 as Pakstan by Choudhry Rahmat Ali, a Pakistan Movement activist, who published it in his pamphlet Now or Never, using it as an acronym referring to the names of the five northern regions of British India: Punjab, Kashmir and Baluchistan; the letter i was incorporated to ease pronunciation. Some of the earliest ancient human civilisations in South Asia originated from areas encompassing present-day Pakistan.
The earliest known inhabitants in the region were Soanian during the Lower Paleolithic, of whom stone tools have been found in the Soan Valley of Punjab. The Indus region, which covers most of present day Pakistan, was the site of several successive ancient cultures including the Neolithic Mehrgarh and the Bronze Age Indus Valley Civilisation at Harappa and Mohenjo-Daro; the Vedic period was characterised by an Indo-Aryan culture. Multan was an important Hindu pilgrimage centre; the Vedic civilisation flourished in the ancient Gandhāran city of Takṣaśilā, now Taxila in the Punjab, founded around 1000 BCE. Successive ancient empires and kingdoms ruled the region: the Persian Achaemenid Empire, Alexander the Great's empire in 326 BCE and the Maurya Empire, founded by Chandragupta Maurya and extended by Ashoka the Great, until 185 BCE; the Indo-Greek Kingdom founded by Demetrius of Bactria included Gandhara and Punjab and reached its greatest extent under Menander, prospering the Greco-Buddhist culture in the region.
Taxila had one of the earliest universities and centres of higher education in the world, established during the late Vedic period in 6th century BCE. The school consisted of several monasteries without large dormitories or lecture halls where the religious instruction was provided on an individualistic basis; the ancient university was documented by the invading forces of Alexander the Great, "the like of which had not been seen in Greece," and was recorded by Chinese pilgrims in the 4th or 5th century CE. At its zenith, the Rai Dynasty of Sindh ruled the surrounding territories; the Pala Dynasty was the last Buddhist empire, under Dharmapala and Devapala, stretched across South Asia from what is now Bangladesh through Northern India to Pakistan. The Arab conqueror Muhammad bin Qasim conquered Sindh in 711 CE; the Pakistan government's official chronol
Andhra Pradesh is one of the 29 states of India. Situated in the south-east of the country, it is the seventh-largest state in India, covering an area of 162,970 km2; as per the 2011 census, it is the tenth most populous state, with 49,386,799 inhabitants. The largest city in Andhra Pradesh is Visakhapatnam. Telugu, one of the classical languages of India, is the major and official language of Andhra Pradesh. On 2 June 2014, the north-western portion of Andhra Pradesh was separated to form the new state Telangana and the longtime capital of Andhra Pradesh, was transferred to Telangana as part of the division. However, in accordance with the Andhra Pradesh Reorganisation Act, 2014, Hyderabad was to remain as the acting capital of both Andhra Pradesh and Telangana states for a period of time not exceeding ten years; the new riverfront de facto capital, Amaravati, is under the jurisdiction of the Andhra Pradesh Capital Region Development Authority. Andhra Pradesh has a coastline of 974 km – the second longest coastline among the states of India, after Gujarat – with jurisdiction over 15,000 km2 of territorial waters.
The state is bordered by Telangana in the north-west and Odisha in the north-east, Karnataka in the west, Tamil Nadu in the south, to the east lies the Bay of Bengal. The small enclave of Yanam, a district of Puducherry, lies to the south of Kakinada in the Godavari delta on the eastern side of the state; the state is made up of the two major regions of Rayalaseema, in the inland southwestern part of the state, Coastal Andhra to the east and northeast, bordering the Bay of Bengal. The state comprises thirteen districts in total, nine of which are located in Coastal Andhra and four in Rayalaseema; the largest city and commercial hub of the state are Visakhapatnam, located on the Bay of Bengal, with a GDP of US$43.5 billion. The economy of Andhra Pradesh is the seventh-largest state economy in India with ₹8.70 lakh crore in gross domestic product and a per capita GDP of ₹142,000. Andhra Pradesh hosted 121.8 million visitors in 2015, a 30% growth in tourist arrivals over the previous year, making it the third most-visited state in India.
The Tirumala Venkateswara Temple in Tirupati is one of the world's most visited religious sites, with 18.25 million visitors per year. Other pilgrimage centres in the state include the Mallikarjuna Jyotirlinga at Srisailam, the Srikalahasteeswara Temple at Srikalahasti, the Ameen Peer Dargah in Kadapa, the Mahachaitya at Amaravathi, the Kanaka Durga Temple in Vijayawada, Prasanthi Nilayam in Puttaparthi; the state's natural attractions include the beaches of Visakhapatnam, hill stations such as the Araku Valley and Horsley Hills, the island of Konaseema in the Godavari River delta. A tribe named. According to Aitareya Brahmana of the Rig Veda, the Andhra left north India and settled in south India; the Satavahanas have been mentioned by the names Andhra, Andhrara-jateeya and Andhrabhrtya in the Puranic literature. They did not refer themselves as Andhra in any of their inscriptions. Archaeological evidence from places such as Amaravati and Vaddamanu suggests that the Andhra region was part of the Mauryan Empire.
Amaravati might have been a regional centre for the Mauryan rule. After the death of Emperor Ashoka, Mauryan rule weakened around 200 BCE and was replaced by several smaller kingdoms in the Andhra region; the Satavahana dynasty dominated the Deccan region from the 1st century BC to the 3rd century. The Satavahanas made Dharanikota and Amaravathi their capital, which according to the Buddhists is the place where Nagarjuna, the philosopher of Mahayana lived in the 2nd and 3rd centuries; the Andhra Ikshvakus, with their capital at Vijayapuri, succeeded the Satavahanas in the Krishna River valley in the latter half of the 2nd century. Pallavas, who were executive officers under the Satavahana kings, were not a recognised political power before the 2nd century AD and were swept away by the Western Chalukyan invasion, led by Pulakesin II in the first quarter of the 7th century CE. After the downfall of the Ikshvakus, the Vishnukundinas were the first great dynasty in the 5th and 6th centuries, held sway over the entire Andhra country, including Kalinga and parts of Telangana.
They played an important role in the history of Deccan during the 5th and 6th century CE, with Eluru and Puranisangam. The Salankayanas were an ancient dynasty that ruled the Andhra region between Godavari and Krishna with their capital at Vengi from 300 to 440 CE; the Eastern Chalukyas of Vengi, whose dynasty lasted for around five hundred years from the 7th century until 1130 C. E. merged with the Chola empire. They continued to rule under the protection of the Chola empire until 1189 C. E. when the kingdom succumbed to the Hoysalas and the Yadavas. The roots of the Telugu language have been seen on inscriptions found near the Guntur district and from others dating to the rule of Renati Cholas in the fifth century CE. Kakatiyas constructed several forts, they were succeeded by the Musunuri Nayaks. The Reddy dynasty was established by Prolaya Vema Reddi in the early 14th century, who ruled from present day Kondaveedu. Prolaya Vema Reddi was part of the confederation of states that started a movement against the invading Turkic Muslim armies of the Delhi
Punjab is a state in northern India. Forming part of the larger Punjab region of the Indian subcontinent, the state is bordered by the Indian states of Jammu and Kashmir to the north, Himachal Pradesh to the east, Haryana to the south and southeast, Rajasthan to the southwest, the Pakistani province of Punjab to the west; the state covers an area of 1.53 % of India's total geographical area. It is the 20th-largest Indian state by area. With 27,704,236 inhabitants at the 2011 census, Punjab is the 16th-largest state by population, comprising 22 districts. Punjabi is the most spoken and official language of the state; the main ethnic group are the Punjabis, with Sikhs forming the demographic majority and Hindus forming a sizable minority. The state capital is Chandigarh, a Union Territory and the capital of the neighbouring state of Haryana; the five rivers from which the region took its name were Sutlej, Beas and Jhelum. The Punjab region was home to the Indus Valley Civilization until 1900 BCE.
The Punjab was invaded by Alexander the Great in 330 BCE and was captured by Chandragupta Maurya under Chanakya. The Punjab was home to the Gupta Empire, the empire of the Alchon Huns, the empire of Harsha, the Mongol Empire. Circa 1000, the Punjab was part of the Delhi Sultanate and Mughal Empire. Sikhism originated in Punjab and resulted in the formation of the Sikh Confederacy after the fall of the Mughal Empire; the confederacy was united into the Sikh Empire by Maharaja Ranjit Singh. The entire Punjab region was annexed by the British East India Company from the Sikh Empire in 1849. In 1947, the Punjab Province of British India was divided along religious lines into West Punjab and East Punjab; the western part was assimilated into new country of Pakistan. The Indian Punjab as well as PEPSU was divided into three parts on the basis of language in 1966. Haryanvi-speaking areas were carved out as Haryana, while the hilly regions and Pahari-speaking areas formed Himachal Pradesh, alongside the current state of Punjab.
Punjab's government has three branches – executive and legislative. Punjab follows the parliamentary system of government with the Chief Minister as the head of the state. Punjab is agriculture-based due to the presence of abundant water sources and fertile soils. Other major industries include the manufacturing of scientific instruments, agricultural goods, electrical goods, financial services, machine tools, sewing machines, sports goods, tourism, bicycles and the processing of pine oil and sugar. Minerals and energy resources contribute to Punjab's economy to a much lesser extent. Punjab has the largest number of steel rolling mill plants in India, which are in "Steel Town"—Mandi Gobindgarh in the Fatehgarh Sahib district; the region was called Sapta Sindhu, the Vedic land of the seven rivers flowing into the ocean. The Sanskrit name for the region, as mentioned in the Ramayana and Mahabharata for example, was Panchanada which means "Land of the Five Rivers", was translated to Persian as Punjab after the Muslim conquests.
The word Punjab is a compound of the Persian words āb. Thus Panjāb means "the land of five rivers"; the five rivers are the Sutlej, Ravi and Jehlum. Traditionally, in English, there used to be a definite article before the name, i.e. "The Punjab". The name is sometimes spelled as "Panjab"; the Greeks called Punjab an inland delta of five converging rivers. During the period when the epic Mahabharata was written, around 800–400 BCE, Punjab was known as Trigarta and ruled by Katoch kings; the Indus Valley Civilization spanned much of the Punjab region with cities such as Ropar. The Vedic Civilization spread along the length of the Sarasvati River to cover most of northern India including Punjab; this civilisation shaped subsequent cultures in the Indian subcontinent. The Punjab region was ruled by many ancient empires including the Gandhara, Mauryas, Kushans, Palas, Gurjara-Pratiharas and Hindu Shahis; the furthest eastern extent of Alexander the Great's exploration was along the Indus River. Agriculture flourished and trading cities such as Jalandhar and Ludhiana grew in wealth.
Due to its location, the Punjab region came under constant attack and influence from both west and east. Punjab faced invasions by the Achaemenids, Scythians and Afghans; this resulted in the Punjab witnessing centuries of bitter bloodshed. Its culture combines Hindu, Islamic and British influences; the original Punjab region is now divided into several units: West Punjab, portions of Khyber-Pakhtunkhwa such as the Gandharar region, the Indian states of Punjab and Himachal Pradesh and the Indian Union territory of Chandigarh and Jammu Division. The Punjab is the'Sapta Sindhu' region mentioned in the Rig Veda, the seven rivers are: Saraswati, Satadru/Shutadri, Asikani, Purushni, Vitasta/Vet and Sindhu. Among the classic books that were wholly or composed in this region are the following. Rigveda Grammar of Sakatayana Ashtadhyayi of Pāṇini Nirukta of Yaska Charaka Samhita Mahabharata along with the Bhagavad Gita Brihatkatha of Gunadya Bakhshali ManuscriptThe world's oldest university Takshashila flourished here before the Buddha's birth.
The Brahmins of this region
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
The Ganges, or Ganga, is a trans-boundary river of the Indian subcontinent which flows through the nations of India and Bangladesh. The 2,525 km river rises in the western Himalayas in the Indian state of Uttarakhand, flows south and east through the Gangetic Plain of North India. After entering West Bengal, it divides into two rivers: the Padma River; the Hooghly, or Adi Ganga, flows through several districts of West Bengal and into the Bay of Bengal near Sagar Island. The other, the Padma flows into and through Bangladesh, joins the Meghna river which empties into the Bay of Bengal; the Ganges is one of the most sacred rivers to Hindus. It is a lifeline to millions of Indians who live along its course and depend on it for their daily needs, it is worshipped in Hinduism and personified as the goddess Gaṅgā. It has been important with many former provincial or imperial capitals located on its banks; the Ganges is polluted. Pollution threatens not only humans, but more than 140 fish species, 90 amphibian species and the endangered Ganges river dolphin.
The Ganges is a major source of global ocean plastic pollution. The levels of fecal coliform bacteria from human waste in the waters of the river near Varanasi are more than 100 times the Indian government's official limit; the Ganga Action Plan, an environmental initiative to clean up the river, has been a major failure thus far, due to rampant corruption, lack of will on behalf of the government and its bureaucracy, lack of technical expertise, poor environmental planning, lack of support from religious authorities. The main stream of Ganga begins at the confluence of the Bhagirathi and Alaknanda rivers in the town of Devprayag in the Garhwal division of the Indian state of Uttarakhand; the Bhagirathi is considered to be the source in Hindu culture and mythology, although the Alaknanda is longer, therefore, hydrologically the source stream. The headwaters of the Alakananda are formed by snowmelt from peaks such as Nanda Devi and Kamet; the Bhagirathi rises at the foot of Gangotri Glacier, at Gomukh, at an elevation of 3,892 m, being mythologically referred to as, residing in the matted locks of Shiva, symbolically Tapovan, being a meadow of ethereal beauty at the feet of Mount Shivling, just 5 km away.
Although many small streams comprise the headwaters of Ganga, the six longest and their five confluences are considered sacred. The six headstreams are the Alaknanda, Nandakini, Pindar and Bhagirathi rivers; the five confluences, known as the Panch Prayag, are all along the Alaknanda. They are, in downstream order, where the Dhauliganga joins the Alaknanda. After flowing 250 km through its narrow Himalayan valley, Ganga emerges from the mountains at Rishikesh debouches onto the Gangetic Plain at the pilgrimage town of Haridwar. At Haridwar, a dam diverts some of its waters into the Ganga Canal, which irrigates the Doab region of Uttar Pradesh, whereas the river, whose course has been southwest until this point, now begins to flow southeast through the plains of northern India; the Ganga follows an 800 km arching course passing through the cities of Kannauj and Kanpur. Along the way it is joined by the Ramganga, which contributes an average annual flow of about 500 m3/s. Ganga joins the river Yamuna at the Triveni Sangam at a holy confluence in Hinduism.
At their confluence the Yamuna is larger than the Ganga, contributing about 2,950 m3/s, or about 58.5% of the combined flow. Now flowing east, the river meets the Tamsa River, which flows north from the Kaimur Range and contributes an average flow of about 190 m3/s. After the Tamsa the Gomti River joins; the Gomti contributes an average annual flow of about 234 m3/s. The Ghaghara River flowing south from the Himalayas of Nepal, joins; the Ghaghara, with its average annual flow of about 2,990 m3/s, is the largest tributary of the Ganges. After the Ghaghara confluence the Ganga is joined from the south by the Son River, contributing about 1,000 m3/s; the Gandaki River the Kosi River, join from the north flowing from Nepal, contributing about 1,654 m3/s and 2,166 m3/s, respectively. The Kosi is the third largest tributary of the Ganga, after the Yamuna; the Kosi merges into the Ganga near Kursela in Bihar. Along the way between Allahabad and Malda, West Bengal, the Ganga passes the towns of Chunar, Varanasi, Patna, Chapra, Ballia, Simaria and Saidpur.
At Bhagalpur, the river begins to flow south-southeast and at Pakur, it begins its attrition with the branching away of its first distributary, the Bhāgirathi-Hooghly, which goes on to become the Hooghly River. Just before the border with Bangladesh the Farakka Barrage controls the flow of Ganga, diverting some of the water into a feeder canal linked to the Hooghly for the purpose of keeping it silt-free; the Hooghly River is formed by the confluence of the Bhagirathi River and Jalangi River at Nabadwip, Hooghly has a number of tributaries of its own. The largest is the Damoda