Tuesday, 5 May 2009

Most African-Americans originated in West Africa, continent has the most genetic variation

WASHINGTON (AP) — Africans have more genetic variation than anyone else on Earth, according to a new study that helps narrow the location where humans first evolved, probably near the South Africa-Namibia border.

The largest study of African genetics ever undertaken also found that nearly three-fourths of African-Americans can trace their ancestry to West Africa. The new analysis published Thursday in the online edition of the journal Science.

"Given the fact that modern humans arose in Africa, they have had time to accumulate dramatic changes" in their genes, explained lead researcher Sarah Tishkoff, a geneticist at the University of Pennsylvania.

People have been adapting to very diverse environmental niches in Africa, she explained in a briefing.

Over 10 years, Tishkoff and an international team of researchers trekked across Africa collecting samples to compare the genes of various peoples. Often working in primitive conditions, the researchers sometimes had to resort to using a car battery to power their equipment, Tishkoff explained.


The reason for their work? Very little was known about the genetic variation in Africans, knowledge that is vital to understanding why diseases have a greater impact in some groups than others and in designing ways to counter those illnesses.

Scott M. Williams of Vanderbilt University noted that constructing patterns of disease variations can help determine which genes predispose a group to a particular illness.

This study "provides a critical piece in the puzzle," he said. For example, there are clear differences in prevalence of diseases such as hypertension and prostate cancer across populations, Williams said.

"The human genome describes the complexity of our species," added Muntaser Ibrahim of the department of molecular biology at the University of Khartoum, Sudan. "Now we have spectacular insight into the history of the African population ... the oldest history of mankind.

"Everybody's history is part of African history because everybody came out of Africa," Ibrahim said.

Christopher Ehret of the department of history at the University of California, Los Angeles, compared genetic variation among people to variations in language.

There are an estimated 2,000 distinct language groups in Africa broken into a few broad categories, often but not always following gene flow.

Movement of a language usually involves arrival of new people, Ehret noted, bringing along their genes. But sometimes language is brought by a small "but advantaged" group which can impose their language without significant gene flow.

Overall, the researchers were able to study and compare the genetics of 121 African groups, 60 non-African populations and four African-American groups.

The so-called "Cape-colored" population of South Africa has highest levels of mixed ancestry on the globe, a blend of African, European, East Asian and South Indian, Tishkoff said.

"This will be a great population for study of diseases" that are more common in one group than another, she said.

The study also found that about 71 percent of African-Americans can trace their ancestry to western African origins. They also have between 13 percent and 15 percent European ancestry and a smaller amount of other African origins. There was "very little" evidence for American Indian genes among African-Americans, Tishkoff said.

Ehret added that only about 20 percent of the Africans brought to North America made the trip directly, while most of the rest went first to the West Indies.

And, he added, some local African-American populations, such as the residents of the sea islands off Georgia and South Carolina, can trace their origins to specific regions such as Sierra Leone and Guinea.

The study was funded by the National Cancer Institute, the National Institutes of Health, the Advanced Computing Center for Research and Education at Vanderbilt University, the L.S.B. Leakey and Wenner Gren Foundation, the National Science Foundation, the David and Lucile Packard and Burroughs Wellcome foundations.

RANDOLPH E. SCHMID, AP Science Writer
11:33 PM PDT, April 30, 2009

Science: http://www.sciencemag.org

Monday, 4 May 2009

Namibia Bushmen were first people in ‘Garden of Eden’

The Garden of Eden may not have looked much like its traditional image of a lush, fertile corner of the Earth.

Instead, a genetic study of Africa suggests that the origin of humanity lies in a sandy, inhospitable region near the coastal border of Namibia and Angola.

The area is populated by the Bushmen, or San people, who may be the closest thing to a biblical Adam and Eve. The study even gives the co-ordinates as 12.5° E and 17.5° S.

Scientists suggest that the clicking sounds characteristic of the San’s language may be a remnant of original human speech.

The conclusion emerges from the largest study of African genetics yet, conducted by an international team led by Sarah Tishkoff, of the University of Pennsylvania.

Researchers studied genes from more than 3,000 people in 121 of 2,000 population groups in Africa. The study demonstrated that there was more genetic diversity in Africa than anywhere else on Earth, and found that modern African populations evolved from 14 ancestral ones.

Dr Tishkoff said that the study had traced the origin of mankind on the assumption that the oldest population would have the greatest genetic diversity. That diversity decreases as populations migrate away from the origin. “The source area for migration within Africa was in that area that represents today the San homeland,” she said. “What it’s really reflecting is the high level of diversity we are seeing in the San populations. It’s consistent with other studies that those populations have the most ancient lineages.”

She left open the possibility that the San may have themselves migrated at some point from a Garden of Eden somewhere else. “It’s very possible that those populations may have migrated from another region, such as eastern Africa. If that’s the case, 50,000 years ago they might have been in eastern Africa and that might have been the source of the migration,” she said.

The study also calculated the point from which human beings — perhaps a single tribal band as small as 150 people — left Africa about 50,000 years ago to populate the rest of the world. The exit point lies near the midpoint of the African coast of the Red Sea, at the coordinates 37.5° E, 22.5° N.

The genes of African-American populations were also studied, showing, as expected, that their roots lay principally in West Africa, source of the transatlantic slave trade. The ancestry of African-Americans was 71 per cent from the Niger-Kordofanian population of West Africa, 13 per cent European and 8 per cent other Africans.

Remains of the day

- The ruins of Babylon were discovered in the 19th century in Iraq. Saddam Hussein planned to restore the ancient city, complete with the Hanging Gardens

- Satellite images taken in 2004 of Mount Ararat in Turkey led Hawaiian Christian archaeologists to declare they were “98 per cent sure” they had found Noah’s Ark

- The Hollywood director James Cameron claimed two years ago that the tombs of Jesus and Mary Magdalene, found outside Jerusalem in 1980, were authentic. He said it was proved by DNA analysis

Sources: Times Archive; BBC; National Geographic
By James Bone

Thursday, 5 February 2009

Group Areas Act

(idea)
by StrawberryFrog
Fri May 31 2002 at 12:14:27

The group areas act designated areas of South Africa for people to live, based on their racial classification in the Population Registration Act.
It was passed in 1950 by the National Party and repealed when the ANC came to power in 1994.
The Group Areas Act of 1950 set out a tone of racial segregation. According to the act, certain areas were to be proclaimed: eventually only people of a designated racial group would be able to live and work there.
It applied to members of all racial groups and provided for the imposition of control over the ownership and occupation of land and buildings throughout S.A.
The act established Group Areas Board to advise the minister of planning on the demarcation of Group Areas for members of the various racial groups.
In practice this meant that all white, black, coloured and Asian people in South Africa would have to live in group areas allocated to members of their groups. Their ownership of property and business rights would be confined to those areas. This also meant that many people had to move out of their homes where they had lived for years and go and live in a strange place which they knew little or nothing about because they had occupied a Group Area designated for another race.
Through this Act many of the Blacks in South Africa were removed from the urban areas especially of the Transvaal and Johannesburg regions were they found work as miners. The reasons for this Act presented by the government of the day was that a growing black proletariat in these urban areas could pose a threat to the government because obviously at these urban areas blacks gained a higher standard of living and higher education than they have been subject to in the African reserves or Townships, thus they would have high expectations and would revolt if these expectations were not met.
The goverment showed no indication that they intended to abolish the act. In October 1985 the State President, P.W. Botha said that the act, unlike the Immorality and Mixed marriages act, was not discriminatory. "It is not discriminatory to protect black, coloured and indian communities in their own areas....... If other population groups have rights and a rightful claim to humanitarian treatment, then I say the whites... are also entitled to justice and to live as citizens of the country in the manner they choose." - http://www.history.und.ac.za/soweto/aparthei1.htm
The Apartheid model of the city was a comercial city centre, transitional mixed-use area, white residential, coloured residential, black residential on outskirts.
People's lives were uprooted from District Six to the Cape Flats. They were thrown out from their homes, with little or no compensation, simply because they lived too close to someplace desirable. They watched the land values soar and the shiny new shopping malls go up where they used to live, while they continued to live with poverty and it's hangers on of gangster warlords and alcohol, drugs and drivebys.
They were shipped out to the sticks, and had to pay the state to travel in to town again every day. This travel was subsidised, so Apartheid cost the state as well. But it need not have happened at all.
Add to this the fact that the second half of the twentieth century saw massive urbanisation in South Africa. People leaving the homelands to find a living in the cities were regarded as illegal imigrants. This resulted in informal settlements, squatter camps and land invasions on the outskirts of urban areas, which were resisted, but were eventually recognised by the authorities as a de-facto part of the cities. The shantytowns and thier dwellers were for a long time subject to police harassment. Buldozing thier shacks in the middle of the wet cold winter was a favourite. These squatter camps suffered even more from gangs and crime.
The urban geography of South Africa was radically distorted by Apartheid - the poor do not willingly live furthest from the city centres.
Along with the homelands, the Group areas act was one of the pillars of Grand Apartheid. See also Petty apartheid
The group areas act was repealed when apartheid was dismantled circa 1994. People now live wherever they can afford to. However communities that have now been established for up to fourty years do not disperse overnight, and so the areas remain. Some attempts at compensation have been made.
In some cases, for instance in Hout Bay this new freedom of residence has resulted in new settlements, slums springing up right next to opulent mansions.
Thanks to Frankie for her suggestions.
Originally posted Wed Nov 15 2000 at 20:07:54, and somehow got duplicated and detached from its node. Reposted by Gritchka to try and fix it. Sorry, StrawberryFrog.

Wednesday, 7 January 2009

Zimbabwe

In the central highlands of southern Africa are numerous, scattered remnants of gigantic fortresses and massive stone walls stretching over thousands of acres. These are the ruins of the majestic cities of Great Zimbabwe (1200 - 1450). This ancient African kingdom organized and controlled the gold and ivory caravans that proceeded from the interior to the southeast coast of Africa where tra de was conducted with Arabia and India for textiles, utensils, glassware and weaponry. Great Zimbabwe was eventually replaced by the Mutapa Empire (1450 - 1630) which, in its turn, was succeeded by the kingdom of Changamire.
The Mutapa king had ultimate religious authority over the Shona people. His power was symbolized by the Divine Flame that burned continuously in his court. His subordinate rulers in the countryside had their own individual flames lit from his central Royal Fire. By 1630, the Portuguese, who had been exploring the coasts of Africa for more than a century, conquered the Mutapa Empire. In 1685, though, a local ruler, Changamire, defeated, and drove out, the Portuguese and established a kingdom, named after himself, Changamire, that lasted well into the 19th century.
By the 1880s, however, the nations of Western Europe, having been vastly enriched by centuries of free African labor, were moving determinedly from their largely coastal encampments to carve the continent up into a patchwork of colonies. (The Berlin Conference of 1884 formalized the process.) Britain, of course, was a key player in all of this. Its African gold and diamond mines were essential to the development and maintenance of its globe-spanning empire.
The individual who personified British power and influence in Africa was Cecil Rhodes. In fact, the south central highland region we are referring to, which is today the nation of Zimbabwe, was for a time a British colony called Southern Rhodesia in honor of Cecil Rhodes. Rhodes consolidated the thousands of individual gold and diamond claims by white miners in South Africa, and formed the fabled DeBeers Gold and Diamond mining company which today controls the price of gold and gems worldwide. He worked mightily to create and maintain the adjacent British colonies of South Africa, Southern Rhodesia (Zimbabwe) and Northern Rhodesia (Zambia) and other British holdings.
Rhodes and his followers waged a series of bitter military campaigns, supported by the British army, against the Shona, Ndebele and other African peoples. By 1895, in Southern Rhodesia (Zimbabwe), for example, the Africans were forced off all the good farmland, their movements restricted, and ultimately left no recourse but to work as laborers on "white owned" land. The white population of Southern Rhodesia, never more than 4%, completely controlled the land, the resources, the economy and the government.
During the 1950s and 60s, while most of the European colonies in Africa were gaining their independence, the southern tier of the continent remained firmly under white control. The region was fully occupied by 7 different British and Portuguese colonies. In 1965, when it appeared that Britain intended to grant independence to Southern Rhodesia, with equivalent rights for Blacks and whites, the white settler government seceded from the Empire and declared themselves the independent white-ruled country of "Rhodesia."
The UN instituted some ineffectual sanctions, and Britain looked the other way, refusing to use force to bring its former colony into line. A small, but persistent, guerilla movement soon developed. The well-equipped white Rhodesian army held its own for awhile. However, in 1975, when the adjacent Portuguese colonies of Mozambique and Angola, won their independence with military aid from Cuba, things began to change. Robert Mugabe and other guerilla leaders were soon mounting devastating military attacks in Rhodesia. By 1980, the white Rhodesians surrendered power to the black majority led by Mugabe. They promptly renamed the country Zimbabwe.
For more than 20 years afterwards, Robert Mugabe and the government of Zimbabwe peacefully negotiated with Britain, the white settlers and other interested parties to regain at least some of the land of the Africans. But all to no avail. Finally, now, 22 years after coming to power, they are taking forceful steps to regain their land. These actions have been greeted with hostility by the white farmers, Britain and America. Despite the fact that Rhodesia is a fully sovereign nation, the US is openly threatening to topple the Mugabe government.
The land question is the ultimate question, not only in Zimbabwe but throughout Africa and around the world. Can any country anywhere really be free if its people do not own the very land beneath their feet? No one is watching events in Zimbabwe with more concern than the white minority in South Africa which, though no longer in power, still controls the land, the precious, invaluable land of the richest nation in the Motherland...

By Arthur Lewin

Racial Classification

A racial classification is given to a group of individuals who share a certain number of anthropological traits, which is necessary so that they not be confused with others. There are two aspects which must be distinguished, the phenotypical and genotypical. I have frequently elaborated on these two aspects.
If we speak only of the genotype, I can find a black who, at the level of his chromosomes, is closer to a Swede than Peter Botha is. But what counts in reality is the phenotype. It is the physical appearance which counts. This black, even if on the level of his cells he is closer than Peter Botha, when he is in South Africa he will live in Soweto. Throughout history, it has always been the phenotype which has been at issue; we mustn't lose sight of this fact. The phenotype is a reality, physical appearance is a reality.
Now, every time these relationships are not favorable to the Western cultures, an effort is made to undermine the cultural consciousness of Africans by telling them, `We don't even know what a race is.' What that means is, they do know what a yellow man is, they do know what a white man is. Despite the fact that the white race and the yellow race are derivatives of the black which, itself, was the first to exist as a human race, now we do not want know what it is. If Africans fall into that trap, they'll be going around in circles. They must understand the trap, understand the stakes.
It is the phenotype which as given us so much difficulty throughout history, so it is this which must be considered in these relations. It exists, is a reality and cannot be repudiated.

SOURCES:African Origin of Civilization by Cheikh Anta DiopCivilization or Barbarism by Cheikh Anta Diop

Asian/Pacific Oceanic Roots

Filipinos, Malaysians, Polynesian, Fiji, all from Africans?The Pacific Islanders originally lived in Africa and southern China. These blacks were called East Yi, Nan Yi, Man Yi, Kunlun and Li. Shun-Sheng Ling, observed that: "During ancient times the majority of the inhabitants of the Pacific coast of China belonged to the East Yi. The East Yi people in accordance with the results of our research consisted chiefly of peoples from Polynesia and Micronesia". The East Yi, were a maritime people who inhabited the east coast of Africa, the Asian mainland and the Pacific Islands in ancient times. They built large Lou Chan (tower boats) that could carry many people. The commercial expertise of the Yi was well known because they were such great seamen the term “Yi” was soon identified with the word "Sea" in Chinese. On the Nan Yi, Shi Zhing, wrote in the Mi Kung, that "Following the Huai Yi, all the maritime tribes came to offer their allegiance. For this the credit should be given the Marquis of Lu....As for the maritime tribes, the Huai Yi, Man Mai and Nan Yi had all vowed their fealty and would obey whatever the Marquis of Lu said".

East Yi founded the Chinese Xia and Shang DynastiesThe Oceanic proto-type is believed to have been found at Dzuyang in China. Other skeletal examples of this type come from the Dawenkou culture. At Dawenkou there was skull deformation and extraction of teeth--customs which are similar to the Polynesian group. Chinese archaeologists believe that the Dawenkou people were the Proto-Pacific islanders. The south Chinese share religious customs and blood type with the Pacific islanders. The bird egg motif is found along the eastern coastal region of China. This motif is also established among the Polynesians, whose creator god Tangaroa maui had an identical birth as the founders of the Shang dynasty from a bird's egg. Moreover, the Oceanic people and South Chinese share the same blood type HLA antigen. The languages spoken in the Pacific are called Austronesian. Austronesian refers to the language family of the modern Pacific islanders including those of Polynesia, Micronesia, Indonesia and the Philippines.
This land mass of China was named Sundaland "phontically similar to Sudan." Until very recently, in geological time, the Southeast Asian area extended to the Indonesian islands, the Philippines and across New Guinea to Australia and Tasmania. As the ice melted after the end of the last Ice Age, the sea levels began to rise and the inhabitants of the Sunda(land) shelf retreated to the coast of south China and northern Vietnam. Other groups such as the Negritos or “Anu”, were stranded on many islands as the Pacific ocean covered up Sundaland. Pottery from the lowest levels of sites in southeast Asia is founds in the Philippines. As early as 9000 B.C. the Austronesian speakers had developed elaborate drainage techniques. These people were the Negroids and who developed a similar drainage technique in ancient Egypt for the Nile River. They were a sedentary people practicing horticulture. As early as 5000 B.C. metallurgy was known, and iron was being exploited by the Negroids 3000 years ago. The early Austronesians expanded across Southeast Asia, the Philippines and eastern Indonesia by 5000 B.C. By 4000 B.C. The Negroid people began to leave the mainland and settled islands as far away as Madagascar and Easter Island.

Easter Island's stone heads - similar to the Olmec heads found in ancient America
After 2500 B.C., Oceanic-Africoid people began to invade Micronesia. Many of these people came directly from Africa and Kumarinadu. It was this group that spread a megalithic culture from Africa and India all the way to Southeast Asia and the Pacific. These Melanesian people are very closely related to the Negroid group in modern Africa in culture and language. Southern China was a center of civilization for the black Austronesian and Oceanic peoples. These Blacks were called Yi and Yueh in the Chinese records. They made beautiful bronze drums which were decorated with examples of their sailing craft. The classical Mongoloids formed the Shang-Yin Dynasty, as opposed to the Li min "Black heads", who founded both the Xia, and first Shang dynasty. The Yin drove the Li Min and Yueh people into western China, especially Gansu and Yunnan. From here the blacks moved into Indo-China which was already settled by the Naga and other Afro-Indo groups. The Austronesian Negroids of southern China settled Polynesia after they were forced southward by first classical Mongoloids and later the Zhou and Qin armies. This is supported by the similarity of the Lapita pottery, and the Dapenkeng and Longshan pottery from southern China.
Black Austronesian (Black Chinese)
The earliest Austronesian language speakers appeared on the mainland around 6000 years ago. Except for Formosa and Taiwan, there are no Austronesian speakers on the mainland today. It would appear that the Polynesians learned agriculture from the African Manding. The reference to the Manding (African) in the Pacific should not be surprising because Africans founded the Xia dynasty in China, and would have been among the ethnic groups pushed into south China and thence the Pacific islands by the mongoloid peoples after 500 B.C Other Manding may have settled the islands before then as explorers given the persistence of Manding terms agreeing with Pacific island place names. The Austronesian speakers built the earliest sea going canoes and were great fishermen. During their spread from the mainland to the islands, they took along tubers and fruits. Cereal plant cultivation was not taken with these sea-voyagers as they occupied the islands in Micronesia and Polynesia. These ancient people made their homes atop mounds and used irrigation to grow the crops. They used stone and wooden tools. Black Austronesians are credited with inventing outrigger canoes and even the Chinese Junk and Sampan. Most of the inhabitants of Oceania are Negroids. They made their way eastward from Africa through India, to Southeast Asia, southern China, Indonesia and the islands in the Pacific. Polynesians or Oceanic-Negroids practiced artificial irrigation, megalithic architecture, well developed religion and divine kingship. Matrilineal descent was part of many Pacific societies. The people in this area practiced the Lapita culture. These people were long distance merchants. They were mobile colonists who communicated by sea. The names for the Pacific islands relate to the people who lived on the islands. For example, Melanesia “Maylasia”, means "Black Islands"; Micronesia, means "Small Islands"; and Polynesian, means "Many Islands". The earliest culture of the Pacific was the Lapita culture. It spread in the Pacific area between 1600-1200 B.C. The Lapita culture is characterized by ceramic cooking pots, bowls and dishes. The ceramics are laced with intricate horizontal bands and geometric designs. (Craib 1983) The motifs on the ceramics agree with Polynesian tattoo signs.

(Left to Right) Polynesian, Malaysian, Fiji)
Some of the Lapita people may have been part of the megalithic culture element which invaded the Pacific area directly from Africa. The Oceanic Africoids or Melanesians were expert seamen. Lapita culture was early established in the area of the Bismarck Archipelago. From here bearers of Lapita culture colonized Tonga and Samoa. The Lapita proplr used the stars to navigate the Pacific. There was an extensive network of trade routes extending over 2700 Kilometers. Yueh ethnic groups from southern China began to settle in the Pacific after 500 B.C.. These people spoke Dravidian and African languages. Between A.D. 200 to 700, classical Mongoloids began to dominate Eastern Polynesian. These Mongoloids are called Yin , in the Chinese literature, but they should not be confused with the black Yi ethnic groups who formerly dominated coastal China. Genghis Khan (Temujin) who was the most successful leader of the Mongolian Empire and united the Mongolian tribes was a descendant of the Yi and was a Black Chinese.
Genghis Khan (Temujin)As the Mongoloid people began to occupy the Southeast Asian mainland, the Indo-African populations set out by boat to settle the Polynesian islands. J. Fraser felt that Polynesia had first been settled by Black races from India. E.S. Handy had a theory that the first settlers of the Polynesian islands were Africans. The Dravidian (African) languages are closely related to languages spoken in the Pacific. For example in 1919, Schmidt in Die Gleederung der Australischen Sprachen, presented evidence which pointed to a connection between Dravidian languages and the Australian languages. This theme was also discussed by N.M. Holmes in On the History and Structure of the Australian Languages, he illustrated that the grammar and phonetics of Australian and African languages coincide. Susumu Ohno , and Clyde Ahmad Winters have indicated that the Tamil language was one of the root languages of Japanese. C.A.Winters has shown that the Japanese language and culture also has affinity to the Manding culture and their language. H.B. Hubber in A comparative grammar of the Korean languages and the Dravidian Family, claimed that the Dravidian languages influenced the Korean languages. This view can best be supported by the presence of Negroid people in Korea, before the colonization of the country by the Korean people.The relationship between the Manding and Tamil, and the Austronesian, Korean and Japanese languages results from the spread of the Yueh and East Yi people, from Yunnan, Indo-China and southern China out into the Pacific. The Japanese and Korean languages are classified within the Altaic Superset of languages. The Manding and Dravidian substratum in Japanese, Korean and Hungarian which all belong to the Altaic group highlight the former presence of the Negroid people across Central Asia and the Pacific. Many Polynesians are classified as Mongoloid people, however they show clear genetic characteristics inherited from the African peoples. By A.D. 1000, the Classical Mongoloid people began to mix with the Austroloid and Oceanic (i.e., Indo-African people) peoples. By this time the Mongoloids were hunting Oceanic people to sell as slaves. The peoples of the continental Pacific islands grew many crops. The chief food for these people were sweet potatoes and taro. Their diet was supplemented by fish and pigs. The low-island people lived almost entirely on coconut palm. Wood for houses came from the trunks. The meat of the coconut was used for food. The husks of coconuts were made into ropes and nets.
In conclusion, it is obvious that the Yueh people of the Lapita culture who settled the Pacific islands before the Austronesian expansion after 500 B.C., spoke Indo-African languages related to the Dravidian and Manding African groups. The linguistic evidence makes it clear that West Africans were settled in the Pacific islands long before Lakato culture bearers would have arrived on the East African scene. A comparison of Melanesian, Dravidian, Manding and Polynesian languages show considerable cognation in the area of kinship terms. A review of this material indicates that speakers of these languages lived in dwellings established in sedentary villages, led by chiefs and /or holy men. They hunted with bow and arrow, made pottery and possessed writing. In addition, they share the terms for fish, domesticated animals and root and grain crops, the deity, and major topographical features. The historical and archaeological evidence supports a two wave Indo-African migration to the Pacific. The first wave of Indo-Africans to settle the Pacific were the Yueh people who were forced out of southern China by the Shang Yin and later Zhou warriors after 1500 B.C.. The Yueh probably introduced the Lapita culture, since many of the Longshan people used incised red pottery.

Tuesday, 5 August 2008

Women and National Development i African Countries...

http://www.jstor.org/stable/pdfplus/523721.pdf