Generation (from the Latin generāre, meaning "to beget"), also known as biogenesis, reproduction, or procreation in biological sciences, is the act of producing offspring. In kinship terminology, it is a structural term designating the parent-child relationship. The term is also often used synonymously with cohort in social science, even though some researchers believe that this usage is misleading; under this formulation the term means "people within a delineated population who experience the same significant events within a given period of time." Generation in this sense of birth cohort, also known as a "social generation," is widely used in popular culture, and has been the basis for much social analysis. Serious analysis of generations began in the century, emerging from an increasing awareness of the possibility of permanent social change and the idea of youthful rebellion against the established social order. Some analysts believe that a generation is one of the fundamental social categories in a society, while others view its importance as being overshadowed by other factors such as class, gender, race, education and so on.
Familial generation 
Usually, a familial generation is defined as the number of years equivalent to the average age of a mother at the times she has her children, which for the sake of convenience is traditionally regarded as 25 years; in short, a generation is 25 years. Some define a familial generation as the average time between a mother's first offspring and her daughter's first offspring. Alternatively, the average generation length has been determined by the average age of women at first birth. In 2010, it was 25.4 years old (in the U.S.). This is due to the place it holds in the family unit economics of committing resources toward raising children, and necessitating greater productivity from the parents, usually the male. Factors such as greater industrialisation and demand for cheap female labour, urbanisation, delayed first pregnancy and a greater uncertainty in relationship stability have all contributed to the increase of the generation length from the late 18th century to the present. These changes can be attributed to both societal level factors, such as GDP and state policy, and related individual level variables, particularly a woman's educational attainment. In developed nations the average familial generation length is in the high 20s and has even reached 30 years in some nations. As of 2008, the average generation length in the United States was 25 years, up 3.6 years since 1970. Germany saw the largest increase in generation length over that time period, from 24 years in 1970 to 30 years in 2008. Conversely, generation length has changed little and remains in the low 20s in less developed nations.
Social generation 
Social generations are cohorts of people who were born in the same date range and share similar cultural experiences. The idea of a social generation, in the sense that it is used today, gained currency in the 19th century. Prior to that the concept "generation" had generally referred to family relationships, not broader social groupings. In 1863, French lexicographer Emile Littré had defined a generation as, "all men living more or less at the same time."
However, as the 19th century wore on, several trends promoted a new idea of generations, of a society divided into different categories of people based on age. These trends were all related to the processes of modernisation, industrialisation, or westernisation, which had been changing the face of Europe since the mid-18th century. One was a change in mentality about time and social change. The increasing prevalence of enlightenment ideas encouraged the idea that society and life were changeable, and that civilization could progress. This encouraged the equation of youth with social renewal and change. Political rhetoric in the 19th century often focused on the renewing power of youth influenced by movements such as Young Italy, Young Germany, Sturm und Drang, the German Youth Movement, and other romantic movements. By the end of the 19th century European intellectuals were disposed toward thinking of the world in generational terms, and in terms of youth rebellion and emancipation.
Two important contributing factors to the change in mentality were the change in the economic structure of society. Because of the rapid social and economic change, young men particularly were less beholden to their fathers and family authority than they had been. Greater social and economic mobility allowed them to flout their authority to a much greater extent than had traditionally been possible. Additionally, the skills and wisdom of fathers were often less valuable than they had been due to technological and social change. During this time, the period of time between childhood and adulthood, usually spent at university or in military service, was also increased for many people entering white collar jobs. This category of people was very influential in spreading the ideas of youthful renewal.
Another important factor was the break-down of traditional social and regional identifications. The spread of nationalism and many of the factors that created it (a national press, linguistic homogenisation, public education, suppression of local particularities) encouraged a broader sense of belonging, beyond local affiliations. People thought of themselves increasingly as part of a society, and this encouraged identification with groups beyond the local.
Auguste Comte was the first philosopher to make a serious attempt to systematically study generations. In Cours de philosophie positive Comte suggested that social change is determined by generational change and in particular conflict between successive generations. As the members of a given generation age, their "instinct of social conservation" becomes stronger, which inevitably and necessarily brings them into conflict with the "normal attribute of youth"— innovation. Other important theorists of the 19th century were John Stuart Mill and Wilhelm Dilthey.
Karl Mannheim was a seminal figure in the study of generations. He elaborated a theory of generations in his 1923 book The Problem of Generations. He suggested that there had been a division into two primary schools of study of generations until that time: positivists, such as Comte who measured social change in fifteen to thirty year life spans, which he argued reduced history to "a chronological table." The other school, the "romantic-historical" was represented by Dilthey and Martin Heidegger. This school emphasised the individual qualitative experience at the expense of social context.
Mannheim emphasised that the rapidity of social change in youth was crucial to the formation of generations, and that not every generation would come to see itself as distinct. In periods of rapid social change a generation would be much more likely to develop a cohesive character. He also believed that a number of distinct sub-generations could exist. Gilleard and Higgs explain "Mannheim sought to describe three elements making up a generation: a shared temporal location (i.e. generational site or birth cohort), shared historical location (i.e. generation as actuality–exposure to a common period or era), and finally a shared socio-cultural location (i.e. generational consciousness–or 'entelechy')."
Jose Ortega y Gasset was another influential generational theorist of the 20th century.
In the 1990s William Strauss and Neil Howe developed Strauss-Howe generational theory outlining what they saw as a pattern of generations which repeated throughout American history. This theory became quite influential with the public and reignited an interest in the sociology of generations. This interest lead to the creation of an industry of generational consulting, publishing and marketing.
Critics have argued that the concept of a social generation may be over-used and that the differences between generations have been overstated in many cases. "Generational advocates William Strauss and Neil Howe (1991) admit: 'Triumphant in popular culture, the cohort generation has been confined by experts to the shadow world of unproven hypothesis.'" Problems abound with the approach from an academic point of view: difficulty of defining precisely who does and does not belong to a given generation, difficulty in studying the phenomenon using falsifiable experimentation, and the importance of other factors such as race, culture, geography, class, ethnicity and so on.
Generational Theory 
It is important to establish a theoretical framework for talking about any generation. Contemporary society readily, if not naturally, accepts the notion of a generation as a form of differentiation or comparison. The idea of a generation is not new and can be found in ancient literature. However, there are also psychological and sociological dimensions in the sense of belonging and identity that can define a generation.
The concept of a generation is also used to locate particular birth cohorts in specific historical and cultural circumstances, such as the "Baby Boomers." The study of generations is a fascinating phenomenon that links a number of different fields and levels of analysis.
While all generations have similarities, it is simplistic to say they are the same. A recent Pew Research Center report noted the challenge of studying generations: "Generational analysis has a long and distinguished place in social science, and we cast our lot with those scholars who believe it is not only possible, but often highly illuminating, to search for the unique and distinctive characteristics of any given age group of Americans. But we also know this is not an exact science. We are mindful that there are as many differences in attitudes, values, behaviors and lifestyles within a generation as there are between generations. But we believe this reality does not diminish the value of generational analysis; it merely adds to its richness and complexity."
It is not where the birth cohort boundaries are drawn that is important, but how individuals and societies interpret the boundaries and how divisions may shape processes and outcomes. However, the practice of categorizing age cohorts is useful to researchers for the purpose of constructing boundaries in their work.
Generational Tension 
Norman Ryder sheds light on the sociology of the discord between generations suggesting that "Society persists despite the mortality of its individual members, through processes of demographic metabolism and particularly the annual infusion of birth cohorts. These may pose a threat to stability but they also provide the opportunity for societal transformation." Ryder's attempts to understand the dynamics at play between generations. Amanda Grenier offers yet another source of explanation for why generational tensions exist. Grenier asserts that generations develop their own linguistic models that contribute to misunderstanding between age cohorts, "Different ways of speaking exercised by older and younger people exist, and may be partially explained by social historical reference points, culturally determined experiences, and individual interpretations."
List of generations 
Western world 
For the purposes of this list "Western world" can be taken to mean North America, Europe, South America, and Oceania. However, it should also be noted that many variations may exist within the regions, both geographically and culturally which mean that the list is broadly indicative, but necessarily very general. For details see the individual articles.
- The Lost Generation, also known as the Generation of 1914 in Europe, is a term originating with Gertrude Stein to describe those who fought in World War I. The members of the lost generation were typically born between 1883 and 1900.
- The Greatest Generation, also known as the G.I. Generation, is the generation that includes the veterans who fought in World War II. They were born from around 1901 through 1924, coming of age during the Great Depression. Journalist Tom Brokaw dubbed this the Greatest Generation in a book of the same name.
- The Silent Generation, also known as the "Lucky Few" were born 1925 through 1945, is the generation that includes those who were too young to join the service during World War II. It includes most of those who fought during the Korean War. Many had fathers who served in World War I. Generally recognized as the children of the Great Depression, this event during their formative years had a profound impact on them.
- The Baby Boomers are the generation that was born following World War II, generally from 1946 up to 1964, a time that was marked by an increase in birth rates. The term "baby boomer" is sometimes used in a cultural context. Therefore, it is impossible to achieve broad consensus of a precise date definition. The baby boom has been described variously as a "shockwave" and as "the pig in the python." In general, baby boomers are associated with a rejection or redefinition of traditional values; however, many commentators have disputed the extent of that rejection, noting the widespread continuity of values with older and younger generations. In Europe and North America boomers are widely associated with privilege, as many grew up in a time of affluence. One of the features of Boomers was that they tended to think of themselves as a special generation, very different from those that had come before them. In the 1960s, as the relatively large numbers of young people became teenagers and young adults, they, and those around them, created a very specific rhetoric around their cohort, and the change they were bringing about.
- Generation X is generally defined as those born after the baby boom ended. Demographers, historians and commentators use beginning birth dates from the early 1960s to the early 1980s. The term has also been used in different times and places for a number of different subcultures or countercultures since the 1950s.
- Generation Y, also called Millennials,  describes the generation following Generation X. There are no precise dates for when the Millennial generation starts and ends. Commentators have used birth dates ranging somewhere from the latter 1970s or from the early 1980s to the early 2000s.
- Generation Z is a name used (although other terms exist such as Post-Millennials) for the cohort of people born from the early 2000s to the present day who are distinct from the preceding Millennial Generation.
Other areas 
- In China, the Post-80s (Chinese: 八零后世代 or 八零后) (born-after-1980 generation) are those who were born between the year 1980 to 1989 in urban areas of Mainland China. Growing up in modern China, the Post-80s has been characterised by its optimism for the future, newfound excitement for consumerism and entrepreneurship and acceptance of its historic role in transforming modern China into an economic superpower. There is also the similarly named Post-90s (Chinese: 九零后), referring to modern teenagers and college students.
- (Quoted From "Post-80's in Hong Kong" section in Post-80s) Post-80s in Hong Kong and the after-eighty generation in mainland China are for the most part different. The term Post-80s (八十後) came into use in Hong Kong between 2009 and 2010, particularly during the course of the opposition to the Guangzhou-Hong Kong Express Rail Link, during which a group of young activists came to the forefront of the Hong Kong political scene. They are said to be "post-materialist" in outlook, and they are particularly vocal in issues such as urban development, culture and heritage, and political reform. Their campaigns include the fight for the preservation of Lee Tung Street, the Star Ferry Pier and the Queen's Pier, Choi Yuen Tsuen Village, real political reform (on June 23), and a citizen-oriented Kowloon West Art district. Their discourse mainly develops around themes such as anti-colonialism, sustainable development, and democracy.
- In South Korea, generational cohorts are often defined around the democratization of the country, with various schemes suggested including names such as the "democratization generation", 386 generation (also called the "June 3, 1987 generation"), that witnessed the June uprising, the "April 19 generation" (that struggled against the Syngman Rhee regime in 1960), the "June 3 generation" (that struggled against the normalization treaty with Japan in 1964), the "1969 generation" (that struggled against the constitutional revision allowing three presidential terms), and the shinsedae ("new") generation.
- In India, generations tend to follow a pattern similar to the broad western model, although there are still major differences, especially in the older generations. According to one interpretation, Indian independence in 1947 marked a generational shift in India. People born in the 1930s and 1940s tended to be loyal to the new state and tended to adhere to "traditional" divisions of society. Indian "boomers", those born after independence and into the early 1960s, tended to link success to leaving India and were more suspicious of traditional societal institutions. Events like the Indian Emergency made them more sceptical of government. Gen Xers saw an improvement in India's economy and they are more comfortable with diverse perspectives. Generation Y continues this pattern.
Other generations 
The term generation is sometimes applied to a cultural movement, or more narrowly defined group than an entire demographic. Some examples include:
- The Beat Generation, a popular American cultural movement that most social scholars say laid the foundation of the pro-active American counterculture of the 1960s. It consisted of Americans born between the two world wars who came of age in the rise of the automobile era, and the surrounding accessibility they brought to the culturally diverse, yet geographically broad and separated nation.
- Generation Jones is a term coined by Jonathan Pontell to describe the cohort of people born between 1954 and 1965. The term is used primarily in English-speaking countries. Pontell defined Generation Jones as referring to the second half of the post–World War II baby boom  The term also includes first-wave Generation X.
- The Hip Hop Generation, another popular American cultural movement describing a musical and cultural phenomenon that from humble beginnings had an international impact. Coined by author Bakari Kitwana, it describes a generation of people, regardless of race, who came of age in post-segregation America. Kitwana establishes the years 1965-1984, which includes Generation X and Generation Y.
- The Stolen Generation, children of Australian Aboriginal and Torres Strait Islander descent who were removed from their families by the Australian Federal and State government agencies and church missions, under acts of their respective parliaments between approximately 1869 and 1969.
- In Europe, a variety of names have emerged in different countries particularly hard hit following the financial crisis of 2007-2008 to designate young people with limited employment and career prospects. The Generation of €700 is a term popularized by the Greek mass media and refers to educated Greek twixters of urban centers who generally fail to establish a career. Young adults are usually forced into underemployment in temporary and occasional jobs, unrelated to their educational background, and receive the minimum allowable base salary of €700. This generation evolved in circumstances leading to the Greek debt crisis and participated in the 2010–2011 Greek protests. In Spain they are referred to as the mileurista (for 1000€), in France “The Precarious Generation,” and in Italy also the generation of 1000 euros.
- MTV Generation, youth of the late 20th and early 21st centuries who are heavily influenced by popular culture and mass media.
See also 
- Generational accounting
- Intergenerational equity
- Strauss-Howe generational theory
- Transgenerational design
- Generation Gap
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