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Sunday, January 11, 2015

Transhumanism

From Wikipedia, the free encyclopedia

Transhumanism (abbreviated as H+ or h+) is an international cultural and intellectual movement with an eventual goal of fundamentally transforming the human condition by developing and making widely available technologies to greatly enhance human intellectual, physical, and psychological capacities.[1] Transhumanist thinkers study the potential benefits and dangers of emerging technologies that could overcome fundamental human limitations, as well as the ethics of developing and using such technologies.[2] The most common thesis put forward is that human beings may eventually be able to transform themselves into beings with such greatly expanded abilities as to merit the label posthuman.[1]
The contemporary meaning of the term transhumanism was foreshadowed by one of the first professors of futurology, FM-2030, who taught "new concepts of the human" at The New School in the 1960s, when he began to identify people who adopt technologies, lifestyles and worldviews "transitional" to posthumanity as "transhuman".[3] This hypothesis would lay the intellectual groundwork for the British philosopher Max More to begin articulating the principles of transhumanism as a futurist philosophy in 1990 and organizing in California an intelligentsia that has since grown into the worldwide transhumanist movement.[3][4][5]

Influenced by seminal works of science fiction, the transhumanist vision of a transformed future humanity has attracted many supporters and detractors from a wide range of perspectives.[3] Transhumanism has been characterized by one critic, Francis Fukuyama, as among the world's most dangerous ideas,[6] to which Ronald Bailey countered that it is rather the "movement that epitomizes the most daring, courageous, imaginative and idealistic aspirations of humanity".[7]

History

Fountain of Youth, by Lucas Cranach the Elder.

According to Nick Bostrom,[1] transcendentalist impulses have been expressed at least as far back as in the quest for immortality in the Epic of Gilgamesh, as well as in historical quests for the Fountain of Youth, the Elixir of Life, and other efforts to stave off aging and death.

There is debate about whether the philosophy of Friedrich Nietzsche can be considered an influence on transhumanism despite its exaltation of the "Übermensch" (overman or superman), due to its emphasis on self-actualization, rather than technological transformation.[1][8][9][10] The transhumanist philosophies by Max More and Stefan Lorenz Sorgner have been influenced strongly by Nietzschean thinking.[8]

Early transhumanist thinking

Julian Huxley, the biologist who coined the term transhumanism in 1957.

Fundamental ideas of transhumanism were first noted in 1923 by the British geneticist J. B. S. Haldane in his essay Daedalus: Science and the Future, which predicted that great benefits would come from applications of advanced sciences to human biology—and that every such advance would first appear to someone as blasphemy or perversion, "indecent and unnatural". In particular, he was interested in the development of the science of eugenics, ectogenesis (creating and sustaining life in an artificial environment) and the application of genetics to improve human characteristics, such as health and intelligence.

His article inspired academic and popular interest. J. D. Bernal, a crystallographer at Cambridge, wrote The World, the Flesh and the Devil in 1929, in which he speculated on the prospects of space colonization and radical changes to human bodies and intelligence through bionic implants and cognitive enhancement.[11] These ideas have been common transhumanist themes ever since.[1]
The biologist Julian Huxley is generally regarded as the founder of transhumanism, after he coined the term in an article written in 1957:
Up till now human life has generally been, as Hobbes described it, ‘nasty, brutish and short’; the great majority of human beings (if they have not already died young) have been afflicted with misery… we can justifiably hold the belief that these lands of possibility exist, and that the present limitations and miserable frustrations of our existence could be in large measure surmounted… The human species can, if it wishes, transcend itself — not just sporadically, an individual here in one way, an individual there in another way, but in its entirety, as humanity.[12]
This definition differs, albeit not substantially, from the one commonly in use since the 1980s. The ideas raised by these thinkers were explored in the science fiction of the 1960s, notably in Arthur C. Clarke's 2001: A Space Odyssey, in which an alien artifact grants transcendent power to its wielder.[13]

Artificial intelligence and the technological singularity

The concept of the technological singularity, or the ultra-rapid advent of superhuman intelligence, was first proposed by the British cryptologist I. J. Good in 1965:
Let an ultraintelligent machine be defined as a machine that can far surpass all the intellectual activities of any man however clever. Since the design of machines is one of these intellectual activities, an ultraintelligent machine could design even better machines; there would then unquestionably be an 'intelligence explosion,' and the intelligence of man would be left far behind. Thus the first ultraintelligent machine is the last invention that man need ever make. [14]
Computer scientist Marvin Minsky wrote on relationships between human and artificial intelligence beginning in the 1960s.[15] Over the succeeding decades, this field continued to generate influential thinkers such as Hans Moravec and Raymond Kurzweil, who oscillated between the technical arena and futuristic speculations in the transhumanist vein.[16][17] The coalescence of an identifiable transhumanist movement began in the last decades of the 20th century. In 1966, FM-2030 (formerly F. M. Esfandiary), a futurist who taught "new concepts of the human" at The New School, in New York City, began to identify people who adopt technologies, lifestyles and world views transitional to posthumanity as "transhuman".[18] In 1972, Robert Ettinger contributed to the conceptualization of "transhumanity" in his book Man into Superman.[19][20] FM-2030 published the Upwingers Manifesto in 1973.[21]

Growth of transhumanism

Cover of the first issue of h+ Magazine, a web-based quarterly publication that focuses on transhumanism.

The first self-described transhumanists met formally in the early 1980s at the University of California, Los Angeles, which became the main center of transhumanist thought. Here, FM-2030 lectured on his "Third Way" futurist ideology. At the EZTV Media venue, frequented by transhumanists and other futurists, Natasha Vita-More presented Breaking Away, her 1980 experimental film with the theme of humans breaking away from their biological limitations and the Earth's gravity as they head into space.[22][23] FM-2030 and Vita-More soon began holding gatherings for transhumanists in Los Angeles, which included students from FM-2030's courses and audiences from Vita-More's artistic productions. In 1982, Vita-More authored the Transhumanist Arts Statement[24] and, six years later, produced the cable TV show TransCentury Update on transhumanity, a program which reached over 100,000 viewers.

In 1986, Eric Drexler published Engines of Creation: The Coming Era of Nanotechnology,[25] which discussed the prospects for nanotechnology and molecular assemblers, and founded the Foresight Institute. As the first non-profit organization to research, advocate for, and perform cryonics, the Southern California offices of the Alcor Life Extension Foundation became a center for futurists. In 1988, the first issue of Extropy Magazine was published by Max More and Tom Morrow. In 1990, More, a strategic philosopher, created his own particular transhumanist doctrine, which took the form of the Principles of Extropy,[26] and laid the foundation of modern transhumanism by giving it a new definition:[27]
Transhumanism is a class of philosophies that seek to guide us towards a posthuman condition. Transhumanism shares many elements of humanism, including a respect for reason and science, a commitment to progress, and a valuing of human (or transhuman) existence in this life. [...] Transhumanism differs from humanism in recognizing and anticipating the radical alterations in the nature and possibilities of our lives resulting from various sciences and technologies [...].

In 1992, More and Morrow founded the Extropy Institute, a catalyst for networking futurists and brainstorming new memeplexes by organizing a series of conferences and, more importantly, providing a mailing list, which exposed many to transhumanist views for the first time during the rise of cyberculture and the cyberdelic counterculture. In 1998, philosophers Nick Bostrom and David Pearce founded the World Transhumanist Association (WTA), an international non-governmental organization working toward the recognition of transhumanism as a legitimate subject of scientific inquiry and public policy.[28] In 2002, the WTA modified and adopted The Transhumanist Declaration.[29] The Transhumanist FAQ, prepared by the WTA, gave two formal definitions for transhumanism:[30]
  1. The intellectual and cultural movement that affirms the possibility and desirability of fundamentally improving the human condition through applied reason, especially by developing and making widely available technologies to eliminate aging and to greatly enhance human intellectual, physical, and psychological capacities.
  2. The study of the ramifications, promises, and potential dangers of technologies that will enable us to overcome fundamental human limitations, and the related study of the ethical matters involved in developing and using such technologies.
A number of similar definitions have been collected by Anders Sandberg, an academic and prominent transhumanist.[31]

In possible contrast with other transhumanist organizations, WTA officials considered that social forces could undermine their futurist visions and needed to be addressed.[3] A particular concern is the equal access to human enhancement technologies across classes and borders.[32] In 2006, a political struggle within the transhumanist movement between the libertarian right and the liberal left resulted in a more centre-leftward positioning of the WTA under its former executive director James Hughes.[32][33] In 2006, the board of directors of the Extropy Institute ceased operations of the organization, stating that its mission was "essentially completed".[34] This left the World Transhumanist Association as the leading international transhumanist organization. In 2008, as part of a rebranding effort, the WTA changed its name to "Humanity+".[35] Humanity+ and Betterhumans publish h+ Magazine, a periodical edited by R. U. Sirius which disseminates transhumanist news and ideas.[36][37] In 2012, the transhumanist Longevity Party had been initiated as an international union of people who promote the development of scientific and technological means to significant life extension, that for now has more than 30 national organisations.[38][39]

Transhumanist-themed blogs by Zoltan Istvan are in mainstream media on Psychology Today and The Huffington Post.[40][41]

The first transhumanist elected member of a Parliament is Giuseppe Vatinno, in Italy.[42]

Theory

It is a matter of debate whether transhumanism is a branch of posthumanism and how this philosophical movement should be conceptualised with regard to transhumanism. The latter is often referred to as a variant or activist form of posthumanism by its conservative,[6] Christian[43] and progressive[44][45] critics.
A common feature of transhumanism and philosophical posthumanism is the future vision of a new intelligent species, into which humanity will evolve and eventually will supplement or supersede it. Transhumanism stresses the evolutionary perspective, including sometimes the creation of a highly intelligent animal species by way of cognitive enhancement (i.e. biological uplift),[3] but clings to a "posthuman future" as the final goal of participant evolution.[46]

Nevertheless, the idea of creating intelligent artificial beings (proposed, for example, by roboticist Hans Moravec) has influenced transhumanism.[16] Moravec's ideas and transhumanism have also been characterised as a "complacent" or "apocalyptic" variant of posthumanism and contrasted with "cultural posthumanism" in humanities and the arts.[47] While such a "cultural posthumanism" would offer resources for rethinking the relationships between humans and increasingly sophisticated machines, transhumanism and similar posthumanisms are, in this view, not abandoning obsolete concepts of the "autonomous liberal subject", but are expanding its "prerogatives" into the realm of the posthuman.[48] Transhumanist self-characterisations as a continuation of humanism and Enlightenment thinking correspond with this view.

Some secular humanists conceive transhumanism as an offspring of the humanist freethought movement and argue that transhumanists differ from the humanist mainstream by having a specific focus on technological approaches to resolving human concerns (i.e. technocentrism) and on the issue of mortality.[49] However, other progressives have argued that posthumanism, whether it be its philosophical or activist forms, amounts to a shift away from concerns about social justice, from the reform of human institutions and from other Enlightenment preoccupations, toward narcissistic longings for a transcendence of the human body in quest of more exquisite ways of being.[50] In this view, transhumanism is abandoning the goals of humanism, the Enlightenment and progressive politics.

As an alternative, humanist philosopher Dwight Gilbert Jones has proposed a renewed Renaissance humanism through DNA and genome repositories, with each individual genotype (DNA) being instantiated as successive phenotypes (bodies or lives via cloning, Church of Man, 1978). In his view, native molecular DNA "continuity" is required for retaining the "self" and no amount of computing power or memory aggregation can replace the essential "stink" of our true genetic identity, which he terms "genity". Instead, DNA/genome stewardship by an institution analogous to the Jesuits' 400 year vigil is a suggested model for enabling humanism to become our species' common credo, a project he proposed in his speculative novel The Humanist - 1000 Summers (2011), wherein humanity dedicates these coming centuries to harmonizing our planet and peoples.

The philosophy of transhumanism is closely related to technoself studies, an interdisciplinary domain of scholarly research dealing with all aspects of human identity in a technological society focusing on the changing nature of relationships between humans and technology.[citation needed]

Aims

Raymond Kurzweil believes that a countdown to when "human life will be irreversibly transformed" can be made through plotting major world events on a graph.

While many transhumanist theorists and advocates[who?] seek to apply reason, science and technology for the purposes of reducing poverty, disease, disability and malnutrition around the globe,[30] transhumanism is distinctive in its particular focus on the applications of technologies to the improvement of human bodies at the individual level. Many transhumanists[who?] actively assess the potential for future technologies and innovative social systems to improve the quality of all life, while seeking to make the material reality of the human condition fulfill the promise of legal and political equality by eliminating congenital mental and physical barriers.

Transhumanist philosophers[who?] argue that there not only exists a perfectionist ethical imperative for humans to strive for progress and improvement of the human condition, but that it is possible and desirable for humanity to enter a transhuman phase of existence in which humans are in control of their own evolution. In such a phase, natural evolution would be replaced with deliberate change.[citation needed]

Some theorists such as Raymond Kurzweil think that the pace of technological innovation is accelerating and that the next 50 years may yield not only radical technological advances, but possibly a technological singularity, which may fundamentally change the nature of human beings.[51] Transhumanists who foresee this massive technological change generally maintain that it is desirable. However, some are also concerned with the possible dangers of extremely rapid technological change and propose options for ensuring that advanced technology is used responsibly. For example, Bostrom has written extensively on existential risks to humanity's future welfare, including ones that could be created by emerging technologies.[52]

While many people[who?] believe that all transhumanists are striving for immortality, it is not necessarily true. Hank Pellissier, managing director of the Institute for Ethics and Emerging Technologies (2011-2012), surveyed transhumanists. He found that, of the 818 respondents, 23.8% did not want immortality.[53] Some of the reasons argued were boredom, Earth’s overpopulation and the desire "to go to an afterlife".[53]

Ethics

Transhumanists engage in interdisciplinary approaches to understand and evaluate possibilities for overcoming biological limitations by drawing on futurology and various fields of ethics. Unlike many philosophers, social critics and activists who place a moral value on preservation of natural systems, transhumanists see the very concept of the specifically natural as problematically nebulous at best and an obstacle to progress at worst.[54] In keeping with this, many prominent transhumanist advocates[who?] refer to transhumanism's critics, on the political right and left jointly, as "bioconservatives" or "bioluddites", the latter term alluding to the 19th century anti-industrialisation social movement that opposed the replacement of human manual labourers by machines.[55]

A belief of counter-transhumanism is that transhumanism can cause unfair human enhancement in many areas of life, but specifically on the social plane. This can be compared to steroid use, where athletes who use steroids in sports have an advantage over those who do not. The same scenario happens when people have certain neural implants that give them an advantage in the work place and in educational aspects.[56]

Currents

There is a variety of opinions within transhumanist thought. Many[who?] of the leading transhumanist thinkers hold views that are under constant revision and development.[57] Some distinctive currents of transhumanism are identified and listed here in alphabetical order:

Spirituality

Although some transhumanists[who?] report having religious or spiritual views, they are for the most part atheists, agnostics or secular humanists.[28] Despite the prevailing secular attitude, some transhumanists pursue hopes traditionally espoused by religions, such as immortality,[60] while several controversial new religious movements from the late 20th century have explicitly embraced transhumanist goals of transforming the human condition by applying technology to the alteration of the mind and body, such as Raëlism.[62] However, most thinkers associated with the transhumanist movement focus on the practical goals of using technology to help achieve longer and healthier lives, while speculating that future understanding of neurotheology and the application of neurotechnology will enable humans to gain greater control of altered states of consciousness, which were commonly interpreted as spiritual experiences, and thus achieve more profound self-knowledge.[63] Transhumanist Buddhists have sought to explore areas of agreement between various types of Buddhism and Buddhist-derived meditation and mind expanding "neurotechnologies".[64] "Cyborg Buddhists" have been criticised[65] for appropriating mindfulness as a tool for transcending humanness.

Many transhumanists believe in the compatibility between the human mind and computer hardware, with the theoretical implication that human consciousness may someday be transferred to alternative media (a speculative technique commonly known as mind uploading).[66] One extreme formulation of this idea, which some transhumanists are interested in, is the proposal of the Omega Point by Christian cosmologist Frank Tipler. Drawing upon ideas in digitalism, Tipler has advanced the notion that the collapse of the Universe billions of years hence could create the conditions for the perpetuation of humanity in a simulated reality within a megacomputer and thus achieve a form of "posthuman godhood". Tipler's thought was inspired by the writings of Pierre Teilhard de Chardin, a paleontologist and Jesuit theologian who saw an evolutionary telos in the development of an encompassing noosphere, a global consciousness.[67][68][69]

Viewed from the perspective of some Christian thinkers, the idea of mind uploading is asserted to represent a denigration of the human body, characteristic of gnostic manichaean belief.[70] Transhumanism and its presumed intellectual progenitors have also been described as neo-gnostic by non-Christian and secular commentators.[71][72]

The first dialogue between transhumanism and faith was a one-day conference held at the University of Toronto in 2004.[73] Religious critics alone faulted the philosophy of transhumanism as offering no eternal truths nor a relationship with the divine. They commented that a philosophy bereft of these beliefs leaves humanity adrift in a foggy sea of postmodern cynicism and anomie. Transhumanists responded that such criticisms reflect a failure to look at the actual content of the transhumanist philosophy, which, far from being cynical, is rooted in optimistic, idealistic attitudes that trace back to the Enlightenment.[74] Following this dialogue, William Sims Bainbridge, a sociologist of religion, conducted a pilot study, published in the Journal of Evolution and Technology, suggesting that religious attitudes were negatively correlated with acceptance of transhumanist ideas and indicating that individuals with highly religious worldviews tended to perceive transhumanism as being a direct, competitive (though ultimately futile) affront to their spiritual beliefs.[75]

Since 2009, the American Academy of Religion holds a "Transhumanism and Religion" consultation during its annual meeting, where scholars in the field of religious studies seek to identify and critically evaluate any implicit religious beliefs that might underlie key transhumanist claims and assumptions; consider how transhumanism challenges religious traditions to develop their own ideas of the human future, in particular the prospect of human transformation, whether by technological or other means; and provide critical and constructive assessments of an envisioned future that place greater confidence in nanotechnology, robotics and information technology to achieve virtual immortality and create a superior posthuman species.[76]

The physicist and transhumanist thinker Giulio Prisco states that "cosmist religions based on science, might be our best protection from reckless pursuit of superintelligence and other risky technologies". Prisco also recognizes the importance of spiritual ideas, as the ones of Nikolai Fyodorovich Fyodorov to the origins of the transhumanism moviment.

Practice

While some transhumanists[who?] take an abstract and theoretical approach to the perceived benefits of emerging technologies, others have offered specific proposals for modifications to the human body, including heritable ones. Transhumanists are often concerned with methods of enhancing the human nervous system. Though some[who?] propose modification of the peripheral nervous system, the brain is considered the common denominator of personhood and is thus a primary focus of transhumanist ambitions.[77]

As proponents of self-improvement and body modification, transhumanists tend to use existing technologies and techniques that supposedly improve cognitive and physical performance, while engaging in routines and lifestyles designed to improve health and longevity.[78] Depending on their age, some[who?] transhumanists express concern that they will not live to reap the benefits of future technologies. However, many have a great interest in life extension strategies and in funding research in cryonics in order to make the latter a viable option of last resort, rather than remaining an unproven method.[79] Regional and global transhumanist networks and communities with a range of objectives exist to provide support and forums for discussion and collaborative projects.[citation needed]

Technologies of interest

Converging Technologies, a 2002 report exploring the potential for synergy among nano-, bio-, info- and cogno-technologies, has become a landmark in near-future technological speculation.[80]

Transhumanists support the emergence and convergence of technologies including nanotechnology, biotechnology, information technology and cognitive science (NBIC), as well as hypothetical future technologies like simulated reality, artificial intelligence, superintelligence, mind uploading, chemical brain preservation and cryonics. They believe that humans can and should use these technologies to become more than human.[81] Therefore, they support the recognition and/or protection of cognitive liberty, morphological freedom and procreative liberty as civil liberties, so as to guarantee individuals the choice of using human enhancement technologies on themselves and their children.[82] Some speculate that human enhancement techniques and other emerging technologies may facilitate more radical human enhancement no later than at the midpoint of the 21st century. Kurzweil's book The Singularity is Near and Michio Kaku's book Physics of the Future outline various human enhancement technologies and give insight on how these technologies may impact the human race.[51][83]

Some reports on the converging technologies and NBIC concepts have criticised their transhumanist orientation and alleged science fictional character.[84] At the same time, research on brain and body alteration technologies has been accelerated under the sponsorship of the U. S. Department of Defense, which is interested in the battlefield advantages they would provide to the supersoldiers of the United States and its allies.[85] There has already been a brain research program to "extend the ability to manage information", while military scientists are now looking at stretching the human capacity for combat to a maximum 168 hours without sleep.[86]

Neuroscientist Anders Sandberg has been practicing on the method of scanning ultra-thin sections of the brain. This method is being used to help better understand the architecture of the brain. As of now, this method is currently being used on mice. This is the first step towards uploading contents of the human brain, including memories and emotions, onto a computer.[87]

Arts and culture

Transhumanist themes have become increasingly prominent in various literary forms during the period in which the movement itself has emerged. Contemporary science fiction often contains positive renditions of technologically enhanced human life set in utopian (especially techno-utopian) societies. However, science fiction's depictions of enhanced humans or other posthuman beings frequently come with a cautionary twist. The more pessimistic scenarios include many horrific or dystopian tales of human bioengineering gone wrong. In the decades immediately before transhumanism emerged as an explicit movement, many transhumanist concepts and themes began appearing in the speculative fiction of authors of the Golden Age of Science Fiction such as Robert A. Heinlein (Lazarus Long series, 1941-87), A. E. van Vogt (Slan, 1946), Isaac Asimov (I, Robot, 1950), Arthur C. Clarke (Childhood's End, 1953) and Stanisław Lem (Cyberiad, 1967).[3] C. S. Lewis' That Hideous Strength (1945) contains an early critique of transhumanism.
In a series of science fiction novels by Neal Asher, the protagonist is an augmented human who carries out missions for "Earth Central Security", an artificial intelligence and superhuman coalition. The author portrays a variety of augmentations in addition to the copying of memory and human minds into crystals and the presence of both benevolent and malevolent artificial intelligences.
The cyberpunk genre, exemplified by William Gibson's Neuromancer (1984) and Bruce Sterling's Schismatrix (1985), has particularly been concerned with the modification of human bodies. Other novels dealing with transhumanist themes that have stimulated broad discussion of these issues include Blood Music (1985), by Greg Bear; The Xenogenesis Trilogy (1987-1989), by Octavia Butler; The Beggar's Trilogy (1990-94), by Nancy Kress; much of Greg Egan's work since the early 1990s such as Permutation City (1994) and Diaspora (1997); The Culture series of Iain M. Banks; The Bohr Maker (1995), by Linda Nagata; Altered Carbon (2002), by Richard K. Morgan; Oryx and Crake (2003), by Margaret Atwood; The Elementary Particles (Eng. trans. 2001) and The Possibility of an Island (Eng. trans. 2006), by Michel Houellebecq; Mindscan (2005), by Robert J. Sawyer; the Commonwealth Saga (2002-10), by Peter F. Hamilton; and Glasshouse (2005), by Charles Stross. Some of these works are considered part of the cyberpunk genre or its postcyberpunk offshoot.

The Dan Brown novel Inferno and the Zoltan Istvan novel The Transhumanist Wager focus on the theme of transhumanism.[88][89][90][91]

Fictional transhumanist scenarios have also become popular in other media during the late 20th and early 21st centuries. Such treatments are found in comic books (Captain America, 1941; Transmetropolitan, 1997; The Surrogates, 2006), films (2001: A Space Odyssey, 1968; Blade Runner, 1982; Gattaca, 1997), television series (the Cybermen of Doctor Who, 1966; the Borg of Star Trek: The Next Generation, 1989), manga and anime (Galaxy Express 999, 1978; Appleseed, 1985; Ghost in the Shell, 1989; Neon Genesis Evangelion, 1995; and the Gundam metaseries, 1979), video games (Metal Gear Solid, 1998; Deus Ex, 2000; BioShock, 2008; Half-Life 2, 2004; Crysis, 2007; Deus Ex: Human Revolution, 2011[92]) and role-playing games.

Carnal Art, a form of sculpture originated by the French artist Orlan, uses the body as its medium and plastic surgery as its method.[93] The French biological anthropologist Dr. Judith Nicogossian also works on representations of the hybrid body.

Debate

The very notion and prospect of human enhancement and related issues arouse public controversy.[94]
Criticisms of transhumanism and its proposals take two main forms: those objecting to the likelihood of transhumanist goals being achieved (practical criticisms) and those objecting to the moral principles or worldview sustaining transhumanist proposals or underlying transhumanism itself (ethical criticisms). Nonetheless, these two strains sometimes converge and overlap, particularly when considering the ethics of changing human biology in the face of incomplete knowledge.

Critics or opponents[who?] often see transhumanists' goals as posing threats to human values.[95] Some also argue that strong advocacy of a transhumanist approach to improving the human condition might divert attention and resources from social solutions.[3] Sometimes, however, there are strong disagreements about the very principles involved, with divergent views on humanity, human nature and the morality of transhumanist aspirations.[3] At least one public interest organization, the U.S.-based Center for Genetics and Society, was formed, in 2001, with the specific goal of opposing transhumanist agendas that involve transgenerational modification of human biology, such as full-term human cloning and germinal choice technology. The Institute on Biotechnology and the Human Future of the Chicago-Kent College of Law critically scrutinizes proposed applications of genetic and nanotechnologies to human biology in an academic setting.

Some of the most widely known critiques of the transhumanist program refer to novels and fictional films. These works of art, despite presenting imagined worlds rather than philosophical analyses, are used as touchstones for some of the more formal arguments.[3]

Feasibility

In a 1992 book, sociologist Max Dublin pointed to many past failed predictions of technological progress and argued that modern futurist predictions would prove similarly inaccurate. He also objected to what he saw as scientism, fanaticism and nihilism by a few in advancing transhumanist causes. Dublin also said that historical parallels existed between Millenarian religions and Communist doctrines.[96]

Although generally sympathetic to transhumanism, public health professor Gregory Stock is skeptical of the technical feasibility and mass appeal of the cyborgization of humanity predicted by Raymond Kurzweil, Hans Moravec and Kevin Warwick. He said that, throughout the 21st century, many humans would find themselves deeply integrated into systems of machines, but would remain biological. Primary changes to their own form and character would arise not from cyberware, but from the direct manipulation of their genetics, metabolism and biochemistry.[97]

Thinkers[who?] who defend the likelihood of accelerating change point to a past pattern of exponential increases in humanity's technological capacities. Kurzweil developed this position in his 2005 book The Singularity Is Near.

Hubris

It has been argued[by whom?] that, in transhumanist thought, humans attempt to substitute themselves for God. This approach is exemplified by the 2002 Vatican statement Communion and Stewardship: Human Persons Created in the Image of God,[98] in which it is stated that "changing the genetic identity of man as a human person through the production of an infrahuman being is radically immoral", implying, as it would, that "man has full right of disposal over his own biological nature". At the same time, this statement argues that creation of a superhuman or spiritually superior being is "unthinkable", since true improvement can come only through religious experience and "realizing more fully the image of God".
Christian theologians and lay activists of several churches and denominations have expressed similar objections to transhumanism and claimed that Christians attain in the afterlife what radical transhumanism promises, such as indefinite life extension or the abolition of suffering. In this view, transhumanism is just another representative of the long line of utopian movements which seek to create "heaven on earth".[99][100]
The biocomplexity spiral is a depiction of the multileveled complexity of organisms in their environments, which is seen by many critics as the ultimate obstacle to transhumanist ambition.

Another critique is aimed mainly at "algeny" (a portmanteau of alchemy and genetics), which Jeremy Rifkin defined as "the upgrading of existing organisms and the design of wholly new ones with the intent of 'perfecting' their performance".[101] More specifically, it attempts to pursue transhumanist goals by way of genetically modifying human embryos in order to create "designer babies". It emphasizes the issue of biocomplexity and the unpredictability of attempts to guide the development of products of biological evolution. This argument, elaborated in particular by the biologist Stuart Newman, is based on the recognition that cloning and germline genetic engineering of animals are error-prone and inherently disruptive of embryonic development. Accordingly, so it is argued, it would create unacceptable risks to use such methods on human embryos. Performing experiments, particularly ones with permanent biological consequences, on developing humans would thus be in violation of accepted principles governing research on human subjects (see the 1964 Declaration of Helsinki). Moreover, because improvements in experimental outcomes in one species are not automatically transferable to a new species without further experimentation, it is claimed that there is no ethical route to genetic manipulation of humans at early developmental stages.[102]

As a practical matter, however, international protocols on human subject research may not present a legal obstacle to attempts by transhumanists and others to improve their offspring by germinal choice technology. According to legal scholar Kirsten Rabe Smolensky, existing laws would protect parents who choose to enhance their child's genome from future liability arising from adverse outcomes of the procedure.[103]

Religious thinkers allied with transhumanist goals, such as the theologians Ronald Cole-Turner and Ted Peters, reject the first argument, holding that the doctrine of "co-creation" provides an obligation to use genetic engineering to improve human biology.[104][105]

Transhumanists and other supporters of human genetic engineering do not dismiss the second argument out of hand, insofar as there is a high degree of uncertainty about the likely outcomes of genetic modification experiments in humans. However, bioethicist James Hughes suggests that one possible ethical route to the genetic manipulation of humans at early developmental stages is the building of computer models of the human genome, the proteins it specifies and the tissue engineering he argues that it also codes for. With the exponential progress in bioinformatics, Hughes believes that a virtual model of genetic expression in the human body will not be far behind and that it will soon be possible to accelerate approval of genetic modifications by simulating their effects on virtual humans.[3] Public health professor Gregory Stock points to artificial chromosomes as an alleged safer alternative to existing genetic engineering techniques.[97] Transhumanists, therefore, argue that parents have a moral responsibility called procreative beneficence to make use of these methods, if and when they are shown to be reasonably safe and effective, to have the healthiest children possible. They add that this responsibility is a moral judgment best left to individual conscience, rather than imposed by law, in all but extreme cases.
In this context, the emphasis on freedom of choice is called procreative liberty.[3]

Contempt for the flesh

In her 1992 book Science as Salvation, philosopher Mary Midgley traces the notion of achieving immortality by transcendence of the material human body (echoed in the transhumanist tenet of mind uploading) to a group of male scientific thinkers of the early 20th century, including J. B. S. Haldane and members of his circle. She characterizes these ideas as "quasi-scientific dreams and prophesies" involving visions of escape from the body coupled with "self-indulgent, uncontrolled power-fantasies".
Her argument focuses on what she perceives as the pseudoscientific speculations and irrational, fear-of-death-driven fantasies of these thinkers, their disregard for laymen and the remoteness of their eschatological visions.[106]

What is perceived as contempt for the flesh in the writings of Marvin Minsky, Hans Moravec and some transhumanists has also been the target of other critics for what they claim to be an instrumental conception of the human body.[48] Reflecting a strain of feminist criticism of the transhumanist program, philosopher Susan Bordo points to "contemporary obsessions with slenderness, youth and physical perfection", which she sees as affecting both men and women, but in distinct ways, as "the logical (if extreme) manifestations of anxieties and fantasies fostered by our culture."[107] Some critics question other social implications of the movement's focus on body modification. Political scientist Klaus-Gerd Giesen, in particular, has asserted that transhumanism's concentration on altering the human body represents the logical yet tragic consequence of atomized individualism and body commodification within a consumer culture.[71] Artist and filmmaker Tim Holmes sees a similar but subtler danger in the devaluation of the body by the progress of civilization itself, which he says encourages mechanical values of expediency, rather than body values of quality of life, leading us to ever more mechanical, anti-flesh solutions. In his TED talk "The Erotic Crisis", he warns against abandoning the hidden wisdom of the flesh, which cannot be digitally comprehended.[108]

Nick Bostrom asserts that the desire to regain youth, specifically, and transcend the natural limitations of the human body, in general, is pan-cultural and pan-historical, and is therefore not uniquely tied to the culture of the 20th century. He argues that the transhumanist program is an attempt to channel that desire into a scientific project on par with the Human Genome Project and achieve humanity's oldest hope, rather than a puerile fantasy or social trend.[1]

Trivialization of human identity

In the U.S., the Amish are a religious group probably most known for their avoidance of certain modern technologies. Transhumanists draw a parallel by arguing that in the near-future there will probably be "humanish", people who choose to "stay human" by not adopting human enhancement technologies. They believe their choice must be respected and protected.[109]

In his 2003 book Enough: Staying Human in an Engineered Age, environmental ethicist Bill McKibben argued at length against many of the technologies that are postulated or supported by transhumanists, including germinal choice technology, nanomedicine and life extension strategies. He claims that it would be morally wrong for humans to tamper with fundamental aspects of themselves (or their children) in an attempt to overcome universal human limitations, such as vulnerability to aging, maximum life span and biological constraints on physical and cognitive ability. Attempts to "improve" themselves through such manipulation would remove limitations that provide a necessary context for the experience of meaningful human choice. He claims that human lives would no longer seem meaningful in a world where such limitations could be overcome technologically. Even the goal of using germinal choice technology for clearly therapeutic purposes should be relinquished, since it would inevitably produce temptations to tamper with such things as cognitive capacities. He argues that it is possible for societies to benefit from renouncing particular technologies, using as examples Ming China, Tokugawa Japan and the contemporary Amish.[110]

Giuseppe Vattino, a supporter of transhumanism elected as a member of Parliament in Italy, believes that, although transhumanism may make us less human, there are both positive and negative consequences. He believes that transhumanism will make people “less subject to the whims of nature, such as illness or climate extremes”.[111]

Transhumanists and other supporters of technological alteration of human biology, such as science journalist Ronald Bailey, reject as extremely subjective the claim that life would be experienced as meaningless if some human limitations are overcome with enhancement technologies. They argue that these technologies will not remove the bulk of the individual and social challenges humanity faces. They suggest that a person with greater abilities would tackle more advanced and difficult projects and continue to find meaning in the struggle to achieve excellence. Bailey also claims that McKibben's historical examples are flawed and support different conclusions when studied more closely.[112] For example, few groups are more cautious than the Amish about embracing new technologies, but, though they shun television and use horses and buggies, some are welcoming the possibilities of gene therapy since inbreeding has afflicted them with a number of rare genetic diseases.[97]

Genetic divide

Some critics of libertarian transhumanism have focused on the likely socioeconomic consequences in societies in which divisions between rich and poor are on the rise. Bill McKibben, for example, suggests that emerging human enhancement technologies would be disproportionately available to those with greater financial resources, thereby exacerbating the gap between rich and poor and creating a "genetic divide".[110] Even Lee M. Silver, the biologist and science writer who coined the term "reprogenetics" and supports its applications, has expressed concern that these methods could create a two-tiered society of genetically engineered "haves" and "have nots" if social democratic reforms lag behind implementation of enhancement technologies.[113] Critics who make these arguments do not thereby necessarily accept the transhumanist assumption that human enhancement is a positive value: in their view, it should be discouraged, or even banned, because it could confer additional power upon the already powerful. The 1997 film Gattaca depicts a dystopian society in which one's social class depends entirely on genetic modifications and is often cited by critics in support of these views.[3]

These criticisms are also voiced by non-libertarian transhumanist advocates, especially self-described democratic transhumanists, who believe that the majority of current or future social and environmental issues (such as unemployment and resource depletion) need to be addressed by a combination of political and technological solutions (like a guaranteed minimum income and alternative technology). Therefore, on the specific issue of an emerging genetic divide due to unequal access to human enhancement technologies, bioethicist James Hughes, in his 2004 book Citizen Cyborg: Why Democratic Societies Must Respond to the Redesigned Human of the Future, argues that progressives or, more precisely, techno-progressives must articulate and implement public policies (i.e., a universal health care voucher system that covers human enhancement technologies) in order to attenuate this problem as much as possible, rather than trying to ban human enhancement technologies. The latter, he argues, might actually worsen the problem by making these technologies unsafe or available only to the wealthy on the local black market or in countries where such a ban is not enforced.[3]

Threats to morality and democracy

Various arguments have been made to the effect that a society that adopts human enhancement technologies may come to resemble the dystopia depicted in the 1932 novel Brave New World, by Aldous Huxley. Sometimes, as in the writings of Leon Kass, the fear is that various institutions and practices judged as fundamental to civilized society would be damaged or destroyed.[114] In his 2002 book Our Posthuman Future and in a 2004 Foreign Policy magazine article, political economist and philosopher Francis Fukuyama designates transhumanism the world's most dangerous idea because he believes that it may undermine the egalitarian ideals of democracy (in general) and liberal democracy (in particular) through a fundamental alteration of "human nature".[6] Social philosopher Jürgen Habermas makes a similar argument in his 2003 book The Future of Human Nature, in which he asserts that moral autonomy depends on not being subject to another's unilaterally imposed specifications. Habermas thus suggests that the human "species ethic" would be undermined by embryo-stage genetic alteration.[115]
Critics such as Kass, Fukuyama and a variety of authors hold that attempts to significantly alter human biology are not only inherently immoral, but also threaten the social order. Alternatively, they argue that implementation of such technologies would likely lead to the "naturalizing" of social hierarchies or place new means of control in the hands of totalitarian regimes. The AI pioneer Joseph Weizenbaum criticizes what he sees as misanthropic tendencies in the language and ideas of some of his colleagues, in particular Marvin Minsky and Hans Moravec, which, by devaluing the human organism per se, promotes a discourse that enables divisive and undemocratic social policies.[116][citation needed]

In a 2004 article in the libertarian monthly Reason, science journalist Ronald Bailey has contested the assertions of Fukuyama by arguing that political equality has never rested on the facts of human biology. He asserts that liberalism was founded not on the proposition of effective equality of human beings, or de facto equality, but on the assertion of an equality in political rights and before the law, or de jure equality. Bailey asserts that the products of genetic engineering may well ameliorate rather than exacerbate human inequality, giving to the many what were once the privileges of the few. Moreover, he argues, "the crowning achievement of the Enlightenment is the principle of tolerance". In fact, he says, political liberalism is already the solution to the issue of human and posthuman rights since in liberal societies the law is meant to apply equally to all, no matter how rich or poor, powerful or powerless, educated or ignorant, enhanced or unenhanced.[7] Other thinkers who are sympathetic to transhumanist ideas, such as philosopher Russell Blackford, have also objected to the appeal to tradition and what they see as alarmism, involved in Brave New World-type arguments.[117]

Dehumanization

Biopolitical activist Jeremy Rifkin and biologist Stuart Newman accept that biotechnology has the power to make profound changes in organismal identity. They argue against the genetic engineering of human beings because they fear the blurring of the boundary between human and artifact.[102][118] Philosopher Keekok Lee sees such developments as part of an accelerating trend in modernization in which technology has been used to transform the "natural" into the "artifactual".[119] In the extreme, this could lead to the manufacturing and enslavement of "monsters" such as human clones, human-animal chimeras or bioroids, but even lesser dislocations of humans and non-humans from social and ecological systems are seen as problematic. The film Blade Runner (1982) and the novels The Boys From Brazil (1976) and The Island of Doctor Moreau (1896) depict elements of such scenarios, but Mary Shelley's 1818 novel Frankenstein is most often alluded to by critics who suggest that biotechnologies could create objectified and socially unmoored people as well as subhumans. Such critics propose that strict measures be implemented to prevent what they portray as dehumanizing possibilities from ever happening, usually in the form of an international ban on human genetic engineering.[120]

Transhumanists believe that "we are morally obligated to help the human race transcend its biological limits".[121] In fact, they go so far as to call "bioluddites" those who are opposed to them.[121] Though the gamut of transhumanist opinions ranges from those who believe that we will eventually be cyborgs to those who simply want their brains frozen in the hopes of being resuscitated in the future, all have considered the question of the human identity and whether or not it will be compromised. While the concept of being able to do away with negative emotions is appealing in theory, there are possible negative implications. For example, Fukuyama points out that, if we did not have the emotion of aggression, "we wouldn’t be able to defend ourselves".[121] These would not only affect our humanity, but also our interactions with others.[121]

Writing in Reason magazine, Ronald Bailey has accused opponents of research involving the modification of animals as indulging in alarmism when they speculate about the creation of subhuman creatures with human-like intelligence and brains resembling those of Homo sapiens. Bailey insists that the aim of conducting research on animals is simply to produce human health care benefits.[122]

A different response comes from transhumanist personhood theorists who object to what they characterize as the anthropomorphobia fueling some criticisms of this research, which science fiction writer Isaac Asimov termed the "Frankenstein complex". They argue that, provided they are self-aware, human clones, human-animal chimeras and uplifted animals would all be unique persons deserving of respect, dignity, rights and citizenship. They conclude that the coming ethical issue is not the creation of so-called monsters, but what they characterize as the "yuck factor" and "human-racism", that would judge and treat these creations as monstrous.[28][123]

Specter of coercive eugenicism

Some critics of transhumanism allege an ableist bias in the use of such concepts as limitations, enhancement and improvement. Some even see the old eugenics, social Darwinist and master race ideologies and programs of the past as warnings of what the promotion of eugenic enhancement technologies might unintentionally encourage. Some fear future "eugenics wars" as the worst-case scenario: the return of coercive state-sponsored genetic discrimination and human rights violations such as compulsory sterilization of persons with genetic defects, the killing of the institutionalized and, specifically, segregation and genocide of races perceived as inferior.[124] Health law professor George Annas and technology law professor Lori Andrews are prominent advocates of the position that the use of these technologies could lead to such human-posthuman caste warfare.[120][125]

For most of its history, eugenics has manifested itself as a movement to sterilize the genetically unfit against their will and encourage the selective breeding of the genetically fit. The major transhumanist organizations strongly condemn the coercion involved in such policies and reject the racist and classist assumptions on which they were based, along with the pseudoscientific notions that eugenic improvements could be accomplished in a practically meaningful time frame through selective human breeding.[125] Instead, most transhumanist thinkers advocate a "new eugenics", a form of egalitarian liberal eugenics.[126] In their 2000 book From Chance to Choice: Genetics and Justice, non-transhumanist bioethicists Allen Buchanan, Dan Brock, Norman Daniels and Daniel Wikler have argued that liberal societies have an obligation to encourage as wide an adoption of eugenic enhancement technologies as possible (so long as such policies do not infringe on individuals' reproductive rights or exert undue pressures on prospective parents to use these technologies) in order to maximize public health and minimize the inequalities that may result from both natural genetic endowments and unequal access to genetic enhancements.[127] Most transhumanists holding similar views nonetheless distance themselves from the term "eugenics" (preferring "germinal choice" or "reprogenetics")[113] to avoid having their position confused with the discredited theories and practices of early-20th-century eugenic movements.[128]

Existential risks

Struck by a passage from Unabomber Theodore Kaczynski's anarcho-primitivist manifesto (quoted in Kurzweil's 1999 book, The Age of Spiritual Machines[17]), computer scientist Bill Joy became a notable critic of emerging technologies.[129] Joy's 2000 essay "Why The Future Doesn't Need Us" argues that human beings would likely guarantee their own extinction by developing the technologies favored by transhumanists. It invokes, for example, the "grey goo scenario", where out-of-control self-replicating nanorobots could consume entire ecosystems, resulting in global ecophagy.[130] Joy's warning was seized upon by appropriate technology organizations such as the ETC Group. Related notions were also voiced by self-described neo-luddite Kalle Lasn, a culture jammer who co-authored a 2001 spoof of Donna Haraway's 1985 Cyborg Manifesto as a critique of the techno-utopianism he interpreted it as promoting.[131] Lasn argues that high technology development should be completely relinquished since it inevitably serves corporate interests with devastating consequences on society and the environment.[132]

In his 2003 book Our Final Hour, British Astronomer Royal Martin Rees argues that advanced science and technology bring as much risk of disaster as opportunity for progress. However, Rees does not advocate a halt to scientific activity. Instead, he calls for tighter security and perhaps an end to traditional scientific openness.[133] Advocates of the precautionary principle, such as many in the environmental movement, also favor slow, careful progress or a halt in potentially dangerous areas. Some precautionists believe that artificial intelligence and robotics present possibilities of alternative forms of cognition that may threaten human life.[134] The Terminator franchise's doomsday depiction of the emergence of an AI that becomes a superintelligenceSkynet, a malignant computer network which initiates a nuclear war in order to exterminate the human species, has often been cited by some involved in this debate.[135]

Transhumanists do not necessarily rule out specific restrictions on emerging technologies so as to lessen the prospect of existential risk. Generally, however, they counter that proposals based on the precautionary principle are often unrealistic and sometimes even counter-productive as opposed to the technogaian current of transhumanism, which they claim is both realistic and productive. In his television series Connections, science historian James Burke dissects several views on technological change, including precautionism and the restriction of open inquiry. Burke questions the practicality of some of these views, but concludes that maintaining the statu quo of inquiry and development poses hazards of its own, such as a disorienting rate of change and the depletion of our planet's resources. The common transhumanist position is a pragmatic one where society takes deliberate action to ensure the early arrival of the benefits of safe, clean, alternative technology, rather than fostering what it considers to be anti-scientific views and technophobia.[136]

One transhumanist solution proposed by Nick Bostrom is differential technological development, a series of attempts to influence the sequence in which technologies are developed. In this approach, planners would strive to retard the development of possibly harmful technologies and their applications, while accelerating the development of likely beneficial technologies, especially those that offer protection against the harmful effects of others.[52] An argument for an "anti-progressionist and pessimistic version of transhumanism" has also been presented by Phil Torres (aka "Philippe Verdoux").[137]

Human brain

From Wikipedia, the free encyclopedia

Human brain
Skull and brain normal human.svg
Human brain and skull
Cerebral lobes.png
Cerebral lobes: the frontal lobe (pink), parietal lobe (green) and occipital lobe (blue)
Details
Latin Cerebrum
Greek ἐγκέφαλος (enképhalos)
μυαλό (myaló)
System Central nervous system
Internal carotid arteries, vertebral arteries
Internal jugular vein, cerebral veins, external veins, basal vein, terminal vein, choroid vein, cerebellar veins
Precursor Neural tube
Identifiers
TA A14.1.03.001
FMA FMA:50801
Anatomical terminology

The human brain has the same general structure as the brains of other mammals, but has a more developed cerebral cortex than any other. Large animals such as whales and elephants have larger brains in absolute terms, but when measured using the encephalization quotient, which compensates for body size, the human brain is almost twice as large as the brain of the bottlenose dolphin, and three times as large as the brain of a chimpanzee. Much of the expansion comes from the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the cerebral cortex devoted to vision, the visual cortex, is also greatly enlarged in humans.

The human cerebral cortex is a thick layer of neural tissue that covers most of the brain. This layer is folded in a way that increases the amount of surface that can fit into the volume available. The pattern of folds is similar across individuals, although there are many small variations. The cortex is divided into four "lobes", called the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. (Some classification systems also include a limbic lobe and treat the insular cortex as a lobe.) Within each lobe are numerous cortical areas, each associated with a particular function, including vision, motor control, and language. The left and right sides of the cortex are broadly similar in shape, and most cortical areas are replicated on both sides. Some areas, though, show strong lateralization, particularly areas that are involved in language. In most people, the left hemisphere is "dominant" for language, with the right hemisphere playing only a minor role. There are other functions, such as spatiotemporal reasoning, for which the right hemisphere is usually dominant.

Despite being protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood–brain barrier, the human brain is susceptible to damage and disease. The most common forms of physical damage are closed head injuries such as a blow to the head, a stroke, or poisoning by a variety of chemicals that can act as neurotoxins. Infection of the brain, though serious, is rare due to the biological barriers that protect it. The human brain is also susceptible to degenerative disorders, such as Parkinson's disease, multiple sclerosis, and Alzheimer's disease. A number of psychiatric conditions, such as schizophrenia and depression, are thought to be associated with brain dysfunctions, although the nature of such brain anomalies is not well understood.

Scientifically, the techniques that are used to study the human brain differ in important ways from those that are used to study the brains of other mammals. On the one hand, invasive techniques such as inserting electrodes into the brain, or disabling parts of the brain in order to examine the effect on behavior, are used with non-human species, but for ethical reasons, are generally not performed with humans. On the other hand, humans are the only subjects who can respond to complex verbal instructions. Thus, it is often possible to use non-invasive techniques such as functional neuroimaging or EEG recording more productively with humans than with non-humans. Furthermore, some of the most important topics, such as language, can hardly be studied at all except in humans. In many cases, human and non-human studies form essential complements to each other. Individual brain cells (except where tissue samples are taken for biopsy for suspected brain tumors) can only be studied in non-humans; complex cognitive tasks can only be studied in humans. Combining the two sources of information to yield a complete functional understanding of the human brain is an ongoing challenge for neuroscience.

Structure

Human brain viewed from below

The adult human brain weighs on average about 1.5 kg (3.3 lb)[1] with a volume of around 1130 cubic centimetres (cm3) in women and 1260 cm3 in men, although there is substantial individual variation.[2] Neurological differences between the sexes have not been shown to correlate in any simple way with IQ or other measures of cognitive performance.[3] The human brain is composed of neurons, glial cells, and blood vessels. The number of neurons, according to array tomography, has been shown to be about 86 billion neurons in the human brain with a roughly equal number of non-neuronal cells called glia.[4]

The cerebral hemispheres (the cerebrum) form the largest part of the human brain and are situated above other brain structures. They are covered with a cortical layer (the cerebral cortex) which has a convoluted topography.[5] Underneath the cerebrum lies the brainstem, resembling a stalk on which the cerebrum is attached. At the rear of the brain, beneath the cerebrum and behind the brainstem, is the cerebellum, a structure with a horizontally furrowed surface, the cerebellar cortex, that makes it look different from any other brain area. The same structures are present in other mammals, although they vary considerably in relative size. As a rule, the smaller the cerebrum, the less convoluted the cortex. The cortex of a rat or mouse is almost perfectly smooth. The cortex of a dolphin or whale, on the other hand, is more convoluted than the cortex of a human.

The living brain is very soft, having a consistency similar to soft gelatin or soft tofu. Although referred to as grey matter, the live cortex is pinkish-beige in color and slightly off-white in the interior.

General features

Human brain viewed through a mid-line incision

The human brain has many properties that are common to all vertebrate brains, including a basic division into three parts called the forebrain, midbrain, and hindbrain, with interconnected fluid-filled ventricles, and a set of generic vertebrate brain structures including the medulla oblongata and pons of the brainstem, the cerebellum, optic tectum, thalamus, hypothalamus, basal ganglia, olfactory bulb, and many others.

As a mammalian brain, the human brain has special features that are common to all mammalian brains, most notably a six-layered cerebral cortex and a set of structures associated with it, including the hippocampus and amygdala. All vertebrates have a forebrain whose upper surface is covered with a layer of neural tissue called the pallium, but in all except mammals the pallium has a relatively simple three-layered cell structure. In mammals it has a much more complex six-layered cell structure, and is given a different name, the cerebral cortex. The hippocampus and amygdala also originate from the pallium, but are much more complex in mammals than in other vertebrates.

As a primate brain, the human brain has a much larger cerebral cortex, in proportion to body size, than most mammals, and a very highly developed visual system. The shape of the brain within the skull is also altered somewhat as a consequence of the upright position in which primates hold their heads.

As a hominid brain, the human brain is substantially enlarged even in comparison to the brain of a typical monkey. The sequence of evolution from Australopithecus (four million years ago) to Homo sapiens (modern man) was marked by a steady increase in brain size, particularly in the frontal lobes, which are associated with a variety of high-level cognitive functions.

Humans and other primates have some differences in gene sequence, and genes are differentially expressed in many brain regions. The functional differences between the human brain and the brains of other animals also arise from many gene–environment interactions.[6]

Cerebral cortex

Bisection of the head of an adult female, showing the cerebral cortex, with its extensive folding, and the underlying white matter[7]

The dominant feature of the human brain is corticalization. The cerebral cortex in humans is so large that it overshadows every other part of the brain. A few subcortical structures show alterations reflecting this trend. The cerebellum, for example, has a medial zone connected mainly to subcortical motor areas, and a lateral zone connected primarily to the cortex. In humans the lateral zone takes up a much larger fraction of the cerebellum than in most other mammalian species. Corticalization is reflected in function as well as structure. In a rat, surgical removal of the entire cerebral cortex leaves an animal that is still capable of walking around and interacting with the environment.[8] In a human, comparable cerebral cortex damage produces a permanent state of coma. The amount of association cortex, relative to the other two categories of sensory and motor, increases dramatically as one goes from simpler mammals, such as the rat and the cat, to more complex ones, such as the chimpanzee and the human.[9]

The cerebral cortex is essentially a sheet of neural tissue, folded in a way that allows a large surface area to fit within the confines of the skull. When unfolded, each cerebral hemisphere has a total surface area of about 1.3 square feet (0.12 m2).[10] Each cortical ridge is called a gyrus, and each groove or fissure separating one gyrus from another is called a sulcus.

Cortical divisions

Four lobes

Regions of the lateral surface of the brain, and particularly the lobes of the forebrain:
Beigefrontal lobe
Blueparietal lobe
Greenoccipital lobe
Pinktemporal lobe

The cerebral cortex is nearly symmetrical with left and right hemispheres that are approximate mirror images of each other. Each hemisphere is conventionally divided into four "lobes", the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. With one exception, this division into lobes does not derive from the structure of the cortex itself, though: the lobes are named after the bones of the skull that overlie them, the frontal bone, parietal bone, temporal bone, and occipital bone. The borders between lobes lie beneath the sutures that link the skull bones together. The exception is the border between the frontal and parietal lobes, which lies behind the corresponding suture; instead it follows the anatomical boundary of the central sulcus, a deep fold in the brain's structure where the primary somatosensory cortex and primary motor cortex meet.

Because of the arbitrary way most of the borders between lobes are demarcated, they have little functional significance. With the exception of the occipital lobe, a small area that is entirely dedicated to vision, each of the lobes contains a variety of brain areas that have minimal functional relationship. The parietal lobe, for example, contains areas involved in somatosensation, hearing, language, attention, and spatial cognition. In spite of this heterogeneity, the division into lobes is convenient for reference. The main functions of the frontal lobe are to control attention, abstract thinking, behavior, problem solving tasks, and physical reactions and personality.[11] The occipital lobe is the smallest lobe; its main functions are visual reception, visual-spatial processing, movement, and color recognition.[12] The temporal lobe controls auditory and visual memories, language, and some hearing and speech.[11]

Major sulci and gyri

Major gyri and sulci on the lateral surface of the cortex
Lateral surface of the cerebral cortex
Medial surface of the cerebral cortex

Although there are enough variations in the shape and placement of gyri and sulci (cortical folds) to make every brain unique, most human brains show sufficiently consistent patterns of folding that allow them to be named. Many of the gyri and sulci are named according to the location on the lobes or other major folds on the cortex. These include:

Functional divisions

Researchers who study the functions of the cortex divide it into three functional categories of regions. One consists of the primary sensory areas, which receive signals from the sensory nerves and tracts by way of relay nuclei in the thalamus. Primary sensory areas include the visual area of the occipital lobe, the auditory area in parts of the temporal lobe and insular cortex, and the somatosensory cortex in the parietal lobe. A second category is the primary motor cortex, which sends axons down to motor neurons in the brainstem and spinal cord.[13] This area occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The third category consists of the remaining parts of the cortex, which are called the association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex processes of perception, thought, and decision-making.[14]

Cytoarchitecture

Brodmann's classification of areas of the cortex

Different parts of the cerebral cortex are involved in different cognitive and behavioral functions. The differences show up in a number of ways: the effects of localized brain damage, regional activity patterns exposed when the brain is examined using functional imaging techniques, connectivity with subcortical areas, and regional differences in the cellular architecture of the cortex. Neuroscientists describe most of the cortex—the part they call the neocortex—as having six layers, but not all layers are apparent in all areas, and even when a layer is present, its thickness and cellular organization may vary. Scientists have constructed maps of cortical areas on the basis of variations in the appearance of the layers as seen with a microscope. One of the most widely used schemes came from Korbinian Brodmann, who split the cortex into 51 different areas and assigned each a number (many of these Brodmann areas have since been subdivided). For example, Brodmann area 1 is the primary somatosensory cortex, Brodmann area 17 is the primary visual cortex, and Brodmann area 25 is the anterior cingulate cortex.[15]

Topography

Topography of the primary motor cortex, showing which body part is controlled by each zone

Many of the brain areas Brodmann defined have their own complex internal structures. In a number of cases, brain areas are organized into "topographic maps", where adjoining bits of the cortex correspond to adjoining parts of the body, or of some more abstract entity. A simple example of this type of correspondence is the primary motor cortex, a strip of tissue running along the anterior edge of the central sulcus, shown in the image to the right. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones. Electrical stimulation of the cortex at any point causes a muscle-contraction in the represented body part. This "somatotopic" representation is not evenly distributed, however. The head, for example, is represented by a region about three times as large as the zone for the entire back and trunk. The size of any zone correlates to the precision of motor control and sensory discrimination possible.= The areas for the lips, fingers, and tongue are particularly large, considering the proportional size of their represented body parts.

In visual areas, the maps are retinotopic—that is, they reflect the topography of the retina, the layer of light-activated neurons lining the back of the eye. In this case too the representation is uneven: the fovea—the area at the center of the visual field—is greatly overrepresented compared to the periphery. The visual circuitry in the human cerebral cortex contains several dozen distinct retinotopic maps, each devoted to analyzing the visual input stream in a particular way. The primary visual cortex (Brodmann area 17), which is the main recipient of direct input from the visual part of the thalamus, contains many neurons that are most easily activated by edges with a particular orientation moving across a particular point in the visual field. Visual areas farther downstream extract features such as color, motion, and shape.

In auditory areas, the primary map is tonotopic. Sounds are parsed according to frequency (i.e., high pitch vs. low pitch) by subcortical auditory areas, and this parsing is reflected by the primary auditory zone of the cortex. As with the visual system, there are a number of tonotopic cortical maps, each devoted to analyzing sound in a particular way.

Within a topographic map there can sometimes be finer levels of spatial structure. In the primary visual cortex, for example, where the main organization is retinotopic and the main responses are to moving edges, cells that respond to different edge-orientations are spatially segregated from one another.

Development

During the first 3 weeks of gestation, the human embryo's ectoderm forms a thickened strip called the neural plate. The neural plate then folds and closes to form the neural tube. This tube flexes as it grows, forming the crescent-shaped cerebral hemispheres at the head, and the cerebellum and pons towards the tail.
Brain of human embryo at 4.5 weeks, showing interior of forebrain 
Brain interior at 5 weeks 
Brain viewed at midline at 3 months 

Function

Cognition

Understanding the mind–body problem – the relationship between the brain and the mind – is a significant challenge both philosophically and scientifically. It is very difficult to imagine how mental activities such as thoughts and emotions could be implemented by physical structures such as neurons and synapses, or by any other type of physical mechanism. This difficulty was expressed by Gottfried Leibniz in an analogy known as Leibniz's Mill:
One is obliged to admit that perception and what depends upon it is inexplicable on mechanical principles, that is, by figures and motions. In imagining that there is a machine whose construction would enable it to think, to sense, and to have perception, one could conceive it enlarged while retaining the same proportions, so that one could enter into it, just like into a windmill. Supposing this, one should, when visiting within it, find only parts pushing one another, and never anything by which to explain a perception.
— Leibniz, Monadology[16]
Incredulity about the possibility of a mechanistic explanation of thought drove René Descartes, and most of humankind along with him, to dualism: the belief that the mind exists independently of the brain.[17]
There has always, however, been a strong argument in the opposite direction. There is clear empirical evidence that physical manipulations of, or injuries to, the brain (for example by drugs or by lesions, respectively) can affect the mind in potent and intimate ways.[18] For example, a person suffering from Alzheimer's disease – a condition that causes physical damage to the brain – also experiences a compromised mind. Similarly, someone who has taken a psychedelic drug may temporarily lose their sense of personal identity (ego death) or experience profound changes to their perception and thought processes. Likewise, a patient with epilepsy who undergoes cortical stimulation mapping with electrical brain stimulation would also, upon stimulation of his or her brain, experience various complex feelings, hallucinations, memory flashbacks, and other complex cognitive, emotional, or behavioral phenomena.[19] Following this line of thinking, a large body of empirical evidence for a close relationship between brain activity and mental activity has led most neuroscientists and contemporary philosophers to be materialists, believing that mental phenomena are ultimately the result of, or reducible to, physical phenomena.[20]

Lateralization

Routing of neural signals from the two eyes to the brain

Each hemisphere of the brain interacts primarily with one half of the body, but for reasons that are unclear, the connections are crossed: the left side of the brain interacts with the right side of the body, and vice versa.[citation needed] Motor connections from the brain to the spinal cord, and sensory connections from the spinal cord to the brain, both cross the midline at the level of the brainstem. Visual input follows a more complex rule: the optic nerves from the two eyes come together at a point called the optic chiasm, and half of the fibers from each nerve split off to join the other. The result is that connections from the left half of the retina, in both eyes, go to the left side of the brain, whereas connections from the right half of the retina go to the right side of the brain. Because each half of the retina receives light coming from the opposite half of the visual field, the functional consequence is that visual input from the left side of the world goes to the right side of the brain, and vice versa. Thus, the right side of the brain receives somatosensory input from the left side of the body, and visual input from the left side of the visual field—an arrangement that presumably is helpful for visuomotor coordination.
The corpus callosum, a nerve bundle connecting the two cerebral hemispheres, with the lateral ventricles directly below

The two cerebral hemispheres are connected by a very large nerve bundle (the largest white matter structure in the brain) called the corpus callosum, which crosses the midline above the level of the thalamus.[21] There are also two much smaller connections, the anterior commissure and hippocampal commissure, as well as many subcortical connections that cross the midline. The corpus callosum is the main avenue of communication between the two hemispheres, though. It connects each point on the cortex to the mirror-image point in the opposite hemisphere, and also connects to functionally related points in different cortical areas.

In most respects, the left and right sides of the brain are symmetrical in terms of function. For example, the counterpart of the left-hemisphere motor area controlling the right hand is the right-hemisphere area controlling the left hand. There are, however, several very important exceptions, involving language and spatial cognition. In most people, the left hemisphere is "dominant" for language: a stroke that damages a key language area in the left hemisphere can leave the victim unable to speak or understand, whereas equivalent damage to the right hemisphere would cause only minor impairment to language skills.

A substantial part of our current understanding of the interactions between the two hemispheres has come from the study of "split-brain patients"—people who underwent surgical transection of the corpus callosum in an attempt to reduce the severity of epileptic seizures. These patients do not show unusual behavior that is immediately obvious, but in some cases can behave almost like two different people in the same body, with the right hand taking an action and then the left hand undoing it. Most of these patients, when briefly shown a picture on the right side of the point of visual fixation, are able to describe it verbally, but when the picture is shown on the left, are unable to describe it, but may be able to give an indication with the left hand of the nature of the object shown.

Language

Locations of two brain areas historically associated with language processing, Broca's area and Wernicke's area, and associated regions of sound processing and speech.
(Associated cortical regions involved in vision, touch sensation, and non-speech movement are also shown.)

The study of how language is represented, processed, and acquired by the brain is neurolinguistics, which is a large multidisciplinary field drawing from cognitive neuroscience, cognitive linguistics, and psycholinguistics. This field originated from the 19th-century discovery that damage to different parts of the brain appeared to cause different symptoms: physicians noticed that individuals with damage to a portion of the left inferior frontal gyrus now known as Broca's area had difficulty in producing language (aphasia of speech), whereas those with damage to a region in the left superior temporal gyrus, now known as Wernicke's area, had difficulty in understanding it.[22]

Since then, there has been substantial debate over what linguistic processes these and other parts of the brain subserve,[23] and although Broca's and Wernicke's areas have traditionally been associated with language functions, they may also be involved in certain non-speech functions.[citation needed] There is also debate over whether or not there even is a strong one-to-one relationship between brain regions and language functions that emerges during neocortical development.[24] More recently, research on language has increasingly used more modern methods including electrophysiology and functional neuroimaging, to examine how language processing occurs. In the study of natural language, a dedicated network of language development has been identified as crucially involving Broca's area.[25][26]

Metabolism

A flat oval object is surrounded by blue. The object is largely green-yellow, but contains a dark red patch at one end and a number of blue patches.
PET image of the human brain showing energy consumption

The brain consumes up to twenty percent of the energy used by the human body, more than any other organ.[27] Brain metabolism normally relies upon blood glucose as an energy source, but during times of low glucose (such as fasting, exercise, or limited carbohydrate intake), the brain will use ketone bodies for fuel with a smaller need for glucose. The brain can also utilize lactate during exercise.[28] Long-chain fatty acids cannot cross the blood–brain barrier, but the liver can break these down to produce ketones. However the medium-chain fatty acids octanoic and heptanoic acids can cross the barrier and be used by the brain.[29][30][31] The brain stores glucose in the form of glycogen, albeit in significantly smaller amounts than that found in the liver or skeletal muscle.[32]

Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization.[33] The need to limit body weight has led to selection for a reduction of brain size in some species, such as bats, who need to be able to fly.[34] The brain mostly uses glucose for energy, and deprivation of glucose, as can happen in hypoglycemia, can result in loss of consciousness. The energy consumption of the brain does not vary greatly over time, but active regions of the cortex consume somewhat more energy than inactive regions: this fact forms the basis for the functional brain imaging methods PET and fMRI.[35] These are nuclear medicine imaging techniques which produce a three-dimensional image of metabolic activity.

Clinical significance

Clinically, death is defined as an absence of brain activity as measured by EEG. Injuries to the brain tend to affect large areas of the organ, sometimes causing major deficits in intelligence, memory, personality, and movement. Head trauma caused, for example, by vehicular or industrial accidents, is a leading cause of death in youth and middle age. In many cases, more damage is caused by resultant edema than by the impact itself. Stroke, caused by the blockage or rupturing of blood vessels in the brain, is another major cause of death from brain damage.

Other problems in the brain can be more accurately classified as diseases. Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and motor neuron diseases are caused by the gradual death of individual neurons, leading to diminution in movement control, memory, and cognition. There are five motor neuron diseases, the most common of which is amyotrophic lateral sclerosis (ALS).

Some infectious diseases affecting the brain are caused by viruses and bacteria. Infection of the meninges, the membranes that cover the brain, can lead to meningitis. Bovine spongiform encephalopathy (also known as "mad cow disease") is deadly in cattle and humans and is linked to prions. Kuru is a similar prion-borne degenerative brain disease affecting humans, (endemic only to Papua New Guinea tribes). Both are linked to the ingestion of neural tissue, and may explain the tendency in human and some non-human species to avoid cannibalism. Viral or bacterial causes have been reported in multiple sclerosis, and are established causes of encephalopathy, and encephalomyelitis.

Mental disorders, such as clinical depression, schizophrenia, bipolar disorder and post-traumatic stress disorder may involve particular patterns of neuropsychological functioning related to various aspects of mental and somatic function. These disorders may be treated by psychotherapy, psychiatric medication, social intervention and personal recovery work or cognitive behavioural therapy; the underlying issues and associated prognoses vary significantly between individuals.

Many brain disorders are congenital, occurring during development. Tay-Sachs disease, fragile X syndrome, and Down syndrome are all linked to genetic and chromosomal errors. Many other syndromes, such as the intrinsic circadian rhythm disorders, are suspected to be congenital as well. Normal development of the brain can be altered by genetic factors, drug use, nutritional deficiencies, and infectious diseases during pregnancy.

Effects of brain damage

A key source of information about the function of brain regions is the effects of damage to them.[36] In humans, strokes have long provided a "natural laboratory" for studying the effects of brain damage.
Most strokes result from a blood clot lodging in the brain and blocking the local blood supply, causing damage or destruction of nearby brain tissue: the range of possible blockages is very wide, leading to a great diversity of stroke symptoms. Analysis of strokes is limited by the fact that damage often crosses into multiple regions of the brain, not along clear-cut borders, making it difficult to draw firm conclusions.

Transient ischemic attacks (TIAs) are mini-strokes that can cause sudden dimming or loss of vision (including amaurosis fugax), speech impairment ranging from slurring to dysarthria or aphasia, and mental confusion. But unlike a stroke, the symptoms of a TIA can resolve within a few minutes or 24 hours. Brain injury may still occur in a TIA lasting only a few minutes.[37][38] A silent stroke or silent cerebral infarct (SCI) differs from a TIA in that there are no immediately observable symptoms. An SCI may still cause long lasting neurological dysfunction affecting such areas as mood, personality, and cognition. An SCI often occurs before or after a TIA or major stroke.[39]

Electroencephalography

By placing electrodes on the scalp it is possible to record the summed electrical activity of the cortex, using a methodology known as electroencephalography (EEG).[40] EEG records average neuronal activity from the cerebral cortex and can detect changes in activity over large areas but with low sensitivity for sub-cortical activity. EEG recordings are sensitive enough to detect tiny electrical impulses lasting only a few milliseconds. Most EEG devices have good temporal resolution, but low spatial resolution.

Electrocorticography

Electrodes can also be placed directly on the surface of the brain (usually during surgical procedures that require removal of part of the skull). This technique, called electrocorticography (ECoG), offers finer spatial resolution than electroencephalography, but is very invasive.

Magnetoencephalography

In addition to measuring the electric field directly via electrodes placed over the skull, it is possible to measure the magnetic field that the brain generates using a method known as magnetoencephalography (MEG).[41] This technique also has good temporal resolution like EEG but with much better spatial resolution. The greatest disadvantage of MEG is that, because the magnetic fields generated by neural activity are very subtle, the neural activity must be relatively close to the surface of the brain to detect its magnetic field. MEGs can only detect the magnetic signatures of neurons located in the depths of cortical folds (sulci) that have dendrites oriented in a way that produces a field.

Imaging

Computed tomography of human brain, from base of the skull to top, taken with intravenous contrast medium

Neuroscientists, along with researchers from allied disciplines, study how the human brain works. Such research has expanded considerably in recent decades. The "Decade of the Brain", an initiative of the United States Government in the 1990s, is considered to have marked much of this increase in research.[42] It has been followed in 2013 by the BRAIN Initiative.

Information about the structure and function of the human brain comes from a variety of experimental methods. Most information about the cellular components of the brain and how they work comes from studies of animal subjects, using techniques described in the brain article. Some techniques, however, are used mainly in humans, and therefore are described here.

Structural and functional imaging

A scan of the brain using fMRI
fMRI scan of the brain

There are several methods for detecting brain activity changes using three-dimensional imaging of local changes in blood flow. The older methods are SPECT and PET, which depend on injection of radioactive tracers into the bloodstream. A newer method, functional magnetic resonance imaging (fMRI), has considerably better spatial resolution and involves no radioactivity.[43] Using the most powerful magnets currently available, fMRI can localize brain activity changes to regions as small as one cubic millimeter. The downside is that the temporal resolution is poor: when brain activity increases, the blood flow response is delayed by 1–5 seconds and lasts for at least 10 seconds. Thus, fMRI is a very useful tool for learning which brain regions are involved in a given behavior, but gives little information about the temporal dynamics of their responses. A major advantage for fMRI is that, because it is non-invasive, it can readily be used on human subjects.

Another new non-invasive functional imaging method is functional near-infrared spectroscopy.

Evolution

A reconstruction of Homo habilis

In the course of evolution of the Homininae, the human brain has grown in volume from about 600 cm3 in Homo habilis to about 1500 cm3 in Homo sapiens neanderthalensis. Subsequently, there has been a shrinking over the past 28,000 years. The male brain has decreased from 1,500 cm3 to 1,350 cm3 while the female brain has shrunk by the same relative proportion.[44] For comparison, Homo erectus, a relative of humans, had a brain size of 1,100 cm3. However, the little Homo floresiensis, with a brain size of 380 cm3, a third of that of their proposed ancestor H. erectus, used fire, hunted, and made stone tools at least as sophisticated as those of H. erectus.[45] In spite of significant changes in social capacity, there has been very little change in brain size from Neanderthals to the present day.[46] "As large as you need and as small as you can" has been said to summarize the opposite evolutionary constraints on human brain size.[47][48] Changes in the size of the human brain during evolution have been reflected in changes in the ASPM and microcephalin genes.[49]

Studies tend to indicate small to moderate correlations (averaging around 0.3 to 0.4) between brain volume and IQ.[50] The most consistent associations are observed within the frontal, temporal, and parietal lobes, the hippocampi, and the cerebellum, but these only account for a relatively small amount of variance in IQ, which itself has only a partial relationship to general intelligence and real-world performance.[51][52][full citation needed] One study indicated that in humans, fertility and intelligence tend to be negatively correlated—that is to say, the more intelligent, as measured by IQ, exhibit a lower total fertility rate than the less intelligent. According to the model, the present rate of decline is predicted to be 1.34 IQ points per decade.[53]

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