William Shockley

William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointly awarded the 1956 Nobel Prize in Physics for "their researches on semiconductors and their discovery of the transistor effect".

For other uses, see William Shockley (disambiguation).
William Shockley
Born
William Bradford Shockley Jr.

(1910-02-13)February 13, 1910
Greater London, England,
United Kingdom
DiedAugust 12, 1989(1989-08-12) (aged 79)
Stanford, California, United States
NationalityAmerican
Alma mater
Known for
Awards
Scientific career
Institutions
Doctoral advisorJohn C. Slater

Partly as a result of Shockley's attempts to commercialize a new transistor design in the 1950s and 1960s, California's "Silicon Valley" became a hotbed of electronics innovation. In his later life, while a professor of electrical engineering at Stanford University, Shockley became a proponent of racism and eugenics.[1][2] A 2019 study in the journal Intelligence found him to be the second-most controversial (behind Arthur Jensen) intelligence researcher among 55 persons covered.[3]

Early life and education

Shockley was born to American parents in London on February 13, 1910, and was raised in his family's hometown of Palo Alto, California from the age of three.[4] His father, William Hillman Shockley, was a mining engineer who speculated in mines for a living and spoke eight languages. His mother, May (née Bradford), grew up in the American West, graduated from Stanford University and became the first female U.S. Deputy mining surveyor.[5] Shockley was homeschooled up to the age of eight, due to his parents' dislike of public schools as well as Shockley's habit of violent tantrums.[6] He spent two years at Palo Alto Military Academy, then briefly enrolled in the Los Angeles Coaching School to study physics and later graduated from Hollywood High School in 1927.[7][8]

Shockley earned his Bachelor of Science degree from Caltech in 1932 and a PhD from MIT in 1936. The title of his doctoral thesis was Electronic Bands in Sodium Chloride, a topic suggested by his thesis advisor, John C. Slater.[9] After receiving his doctorate, Shockley joined a research group headed by Clinton Davisson at Bell Labs in New Jersey. The next few years were productive for Shockley. He published a number of fundamental papers on solid state physics in Physical Review. In 1938, he received his first patent, "Electron Discharge Device", on electron multipliers.[10]

Career

Shockley was one of the first recruits to Bell Labs by Mervin Kelly, who became director of research at the company in 1936 and focused on hiring solid-state physicists. Executives at Bell Labs had theorized that semiconductors may offer solid-state alternatives to the vacuum tubes used throughout Bell's nationwide telephone system. Shockley conceived a number of designs based on copper-oxide semiconductor materials, and with Walter Brattain unsuccessfully attempted to create a prototype in 1939.[11]

When World War II broke out, Shockley prior research was interrupted and he became involved in radar research in Manhattan (New York City). In May 1942, he took leave from Bell Labs to become a research director at Columbia University's Anti-Submarine Warfare Operations Group.[12] This involved devising methods for countering the tactics of submarines with improved convoying techniques, optimizing depth charge patterns, and so on. This project required frequent trips to the Pentagon and Washington, where Shockley met many high-ranking officers and government officials.

In 1944, he organized a training program for B-29 bomber pilots to use new radar bomb sights. In late 1944 he took a three-month tour to bases around the world to assess the results. For this project, Secretary of War Robert Patterson awarded Shockley the Medal for Merit on October 17, 1946.[13]

In July 1945, the War Department asked Shockley to prepare a report on the question of probable casualties from an invasion of the Japanese mainland. Shockley concluded:

If the study shows that the behavior of nations in all historical cases comparable to Japan's has in fact been invariably consistent with the behavior of the troops in battle, then it means that the Japanese dead and ineffectives at the time of the defeat will exceed the corresponding number for the Germans. In other words, we shall probably have to kill at least 5 to 10 million Japanese. This might cost us between 1.7 and 4 million casualties including 400,000 to 800,000 killed.[14]

This report influenced the decision of the United States to drop atomic bombs on Hiroshima and Nagasaki, which precipitated the unconditional surrender of Japan.[15]

Shockley was the first physicist to propose a log-normal distribution to model the creation process for scientific research papers.[16]

Development of the transistor

Shortly after the war ended in 1945, Bell Labs formed a solid-state physics group, led by Shockley and chemist Stanley Morgan, which included John Bardeen, Walter Brattain, physicist Gerald Pearson, chemist Robert Gibney, electronics expert Hilbert Moore, and several technicians. Their assignment was to seek a solid-state alternative to fragile glass vacuum tube amplifiers. Its first attempts were based on Shockley's ideas about using an external electrical field on a semiconductor to affect its conductivity. These experiments failed every time in all sorts of configurations and materials. The group was at a standstill until Bardeen suggested a theory that invoked surface states that prevented the field from penetrating the semiconductor. The group changed its focus to study these surface states and they met almost daily to discuss the work. The rapport of the group was excellent, and ideas were freely exchanged.[17]

By the winter of 1946 they had enough results that Bardeen submitted a paper on the surface states to Physical Review. Brattain started experiments to study the surface states through observations made while shining a bright light on the semiconductor's surface. This led to several more papers (one of them co-authored with Shockley), which estimated the density of the surface states to be more than enough to account for their failed experiments. The pace of the work picked up significantly when they started to surround point contacts between the semiconductor and the conducting wires with electrolytes. Moore built a circuit that allowed them to vary the frequency of the input signal easily. Finally they began to get some evidence of power amplification when Pearson, acting on a suggestion by Shockley, put a voltage on a droplet of glycol borate placed across a P–n junction.[18]

John Bardeen, William Shockley and Walter Brattain at Bell Labs, 1948

Bell Labs' attorneys soon discovered Shockley's field effect principle had been anticipated and devices based on it patented in 1930 by Julius Lilienfeld, who filed his MESFET-like patent in Canada on October 22, 1925.[19][20] Although the patent appeared "breakable" (it could not work) the patent attorneys based one of its four patent applications only on the Bardeen-Brattain point contact design. Three others (submitted first) covered the electrolyte-based transistors with Bardeen, Gibney and Brattain as the inventors.

Shockley's name was not on any of these patent applications. This angered Shockley, who thought his name should also be on the patents because the work was based on his field effect idea. He even made efforts to have the patent written only in his name, and told Bardeen and Brattain of his intentions.[21]

Shockley, angered by not being included on the patent applications, secretly continued his own work to build a different sort of transistor based on junctions instead of point contacts; he expected this kind of design would be more likely to be commercially viable. The point contact transistor, he believed, would prove to be fragile and difficult to manufacture. Shockley was also dissatisfied with certain parts of the explanation for how the point contact transistor worked and conceived of the possibility of minority carrier injection.

On February 13, 1948 another team member, John N. Shive, built a point contact transistor with bronze contacts on the front and back of thin wedge of germanium, proving that holes could diffuse through bulk germanium and not just along the surface as previously thought.[22]:153[23]:145 Shive's invention sparked[24] Shockley's invention of the junction transistor.[22]:143 A few months later he invented an entirely new, considerably more robust, type of transistor with a layer or 'sandwich' structure. This structure went on to be used for the vast majority of all transistors into the 1960s, and evolved into the bipolar junction transistor. Shockley later admitted that the workings of the team were "mixture of cooperation and competition". He also admitted that he kept some of his own work secret until his "hand was forced" by Shive's 1948 advance.[25] Shockley worked out a rather complete description of what he called the "sandwich" transistor, and a first proof of principle was obtained on April 7, 1949.

Meanwhile, Shockley worked on his magnum opus, Electrons and Holes in Semiconductors which was published as a 558-page treatise in 1950. The tome included Shockley's critical ideas of drift and diffusion and the differential equations that govern the flow of electrons in solid state crystals. Shockley's diode equation is also described. This seminal work became the reference text for other scientists working to develop and improve new variants of the transistor and other devices based on semiconductors.[26]

This resulted in his invention of the bipolar "junction transistor", which was announced at a press conference on July 4, 1951.[27]

In 1951, he was elected to the National Academy of Sciences (NAS). He was forty-one years old; this was rather young for such an election. Two years later, he was chosen as the recipient of the prestigious Comstock Prize[28] for Physics by the NAS, and was the recipient of many other awards and honors.

The ensuing publicity generated by the "invention of the transistor" often thrust Shockley to the fore, much to the chagrin of Bardeen and Brattain. Bell Labs management, however, consistently presented all three inventors as a team. Though Shockley would correct the record where reporters gave him sole credit for the invention,[29] he eventually infuriated and alienated Bardeen and Brattain, and he essentially blocked the two from working on the junction transistor. Bardeen began pursuing a theory for superconductivity and left Bell Labs in 1951. Brattain refused to work with Shockley further and was assigned to another group. Neither Bardeen nor Brattain had much to do with the development of the transistor beyond the first year after its invention.[30]

Shockley Semiconductor
Main article: Shockley Semiconductor Laboratory

In 1956 Shockley moved from New Jersey to Mountain View, California to start Shockley Semiconductor Laboratory to live closer to his ailing and elderly mother in Palo Alto, California.[31][32] The company, a division of Beckman Instruments, Inc., was the first establishment working on silicon semiconductor devices in what came to be known as Silicon Valley.

After he received the Nobel Prize in 1956 his demeanor changed, as evidenced in his increasingly autocratic, erratic and hard-to-please management style.[33] Shockley became increasingly domineering and paranoid. In one well-known incident, he demanded lie detector tests to find the "culprit" after a company secretary suffered a minor cut.[34] In late 1957, eight of Shockley's researchers, who would come to be known as the "traitorous eight", resigned after Shockley decided not to continue research into silicon-based semiconductors.[35] They went on to form Fairchild Semiconductor, a loss from which Shockley Semiconductor never recovered and which led to its purchase by another company three years later. Over the course of the next 20 years, more than 65 new enterprises would end up having employee connections back to Fairchild.[36]

A group of about thirty colleagues who had met on and off since 1956 met again at Stanford in 2002 to reminisce about their time with Shockley and his central role in sparking the information technology revolution. The group's organizer said, "Shockley is the man who brought silicon to Silicon Valley."[37]

Views on race and eugenics
See also: Flynn effect and History of the race and intelligence controversy

After Shockley left his role as director of Shockley Semiconductor, he joined Stanford University, where in 1963 he was appointed the Alexander M. Poniatoff Professor of Engineering and Applied Science, in which position he remained until his retirement as professor emeritus in 1975.[38] In this position, Shockley became interested in questions of race, human intelligence, and eugenics. He thought this work was important to the genetic future of the human species and he came to describe it as the most important work of his career, even though expressing his views damaged his reputation. Shockley argued that a higher rate of reproduction among the less intelligent was having a dysgenic effect, and that a drop in average intelligence would ultimately lead to a decline in civilization. He also claimed that blacks were genetically inferior to whites on an intellectual level.[39] For example, in a debate with psychiatrist Frances Cress Welsing M.D. and on Firing Line with William F. Buckley Jr.:

My research leads me inescapably to the opinion that the major cause of the American Negro's intellectual and social deficits is hereditary and racially genetic in origin and, thus, not remediable to a major degree by practical improvements in the environment.[40]

Shockley's writings and lectures on this topic were partly based on the writings of psychologist Cyril Burt and were funded by the Pioneer Fund. Shockley also proposed that individuals with IQs below 100 be paid to undergo voluntary sterilization.[39] Anthropologist Roger Pearson defended Shockley in a self-published book co-authored with Shockley.[41] University of Wisconsin–Milwaukee professor Edgar G. Epps argued that "William Shockley's position lends itself to racist interpretations".[42]

In 1981, Shockley filed a libel suit in Atlanta against the Atlanta Constitution after a science writer, Roger Witherspoon, compared Shockley's advocacy of a voluntary sterilization program to Nazi human experimentation. The suit took three years to go to trial. Shockley won the suit but received only one dollar in damages[43] and no punitive damages. Shockley's biographer Joel Shurkin, a science writer on the staff of Stanford University during those years, sums this up as saying that the statement was defamatory, but Shockley's reputation was not worth much by the time the trial reached a verdict.[44] Shockley taped his telephone conversations with reporters, and then sent the transcript to them by registered mail. At one point he toyed with the idea of making them take a simple quiz on his work before discussing the subject with them. His habit of saving all his papers (including laundry lists) provides abundant documentation for researchers on his life.[45]

Shockley was a candidate for the Republican nomination in the 1982 United States Senate election in California. He ran on a single-issue platform of highlighting the "dysgenic threat" of some racial groups, including African-Americans, to American society.[46][47][48] He came in eighth place in the primary, receiving 8,308 votes and 0.37% of the vote.[49]

Personal life

At age 23 and while still a student, Shockley married Jean Bailey in August 1933. The couple had two sons and a daughter.[50] Although one of his sons earned a PhD at Stanford University and his daughter graduated from Radcliffe College, Shockley believed his children "represent a very significant regression ... my first wife – their mother – had not as high an academic-achievement standing as I had."[39]

Shockley became an accomplished rock climber, going often to the Shawangunks in the Hudson River Valley. He pioneered a route across an overhang, known as "Shockley's Ceiling", which remains one of the classic climbing routes in the area.[18][51] Several climbing guidebooks changed the route's name to "The Ceiling" in 2020 due to controversy associated with Shockley's eugenics research.[52] Shockley was popular as a speaker, lecturer, and an amateur magician. He once "magically" produced a bouquet of roses at the end of his address before the American Physical Society. He was also known in his early years for his elaborate practical jokes.[53]

Shockley donated sperm to the Repository for Germinal Choice, a sperm bank founded by Robert Klark Graham in hopes of spreading humanity's best genes. The bank, called by the media the "Nobel Prize sperm bank", claimed to have three Nobel Prize-winning donors, though Shockley was the only one to publicly acknowledge his involvement. However, Shockley's controversial views brought the Repository for Germinal Choice a degree of notoriety and may have discouraged other Nobel Prize winners from donating sperm.[54]

Death

Shockley died of prostate cancer in 1989 at the age of 79.[55] At the time of his death, he was estranged from most of his friends and family, except his second wife, the former Emmy Lanning (1913–2007). His children reportedly learned of his death by reading his obituary in the newspaper.[56] Shockley is interred at Alta Mesa Memorial Park in Palo Alto, California.

Honors

Patents

Shockley was granted over ninety US patents.[59] Some notable ones are:

  • US 2502488 Semiconductor Amplifier. Apr. 4, 1950; his first granted patent involving transistors.
  • US 2569347 Circuit element utilizing semiconductive material. Sept. 25, 1951; His earliest applied for (June 26, 1948) patent involving transistors.
  • US 2655609 Bistable Circuits. Oct. 13, 1953; Used in computers.
  • US 2787564 Forming Semiconductive Devices by Ionic Bombardment. Apr. 2, 1957; The diffusion process for implantation of impurities.
  • US 3031275 Process for Growing Single Crystals. Apr. 24, 1962; Improvements on process for production of basic materials.
  • US 3053635 Method of Growing Silicon Carbide Crystals. Sept. 11, 1962; Exploring other semiconductors.

Bibliography

Prewar scientific articles by Shockley
  • An Electron Microscope for Filaments: Emission and Adsorption by Tungsten Single Crystals, R. P. Johnson and W. Shockley, Phys. Rev. 49, 436–440 (1936) doi:10.1103/PhysRev.49.436
  • Optical Absorption by the Alkali Halides, J. C. Slater and W. Shockley, Phys. Rev. 50, 705–719 (1936) doi:10.1103/PhysRev.50.705
  • Electronic Energy Bands in Sodium Chloride, William Shockley, Phys. Rev. 50, 754–759 (1936) doi:10.1103/PhysRev.50.754
  • The Empty Lattice Test of the Cellular Method in Solids, W. Shockley, Phys. Rev. 52, 866–872 (1937) doi:10.1103/PhysRev.52.866
  • On the Surface States Associated with a Periodic Potential, William Shockley, Phys. Rev. 56, 317–323 (1939) doi:10.1103/PhysRev.56.317
  • The Self-Diffusion of Copper, J. Steigman, W. Shockley and F. C. Nix, Phys. Rev. 56, 13–21 (1939) doi:10.1103/PhysRev.56.13

Postwar articles by Shockley

Books by Shockley
  • Shockley, William – Electrons and holes in semiconductors, with applications to transistor electronics, Krieger (1956) ISBN 0-88275-382-7
  • Shockley, William and Gong, Walter A – Mechanics Charles E. Merrill, Inc. (1966)
  • Shockley, William and Pearson, Roger – Shockley on Eugenics and Race: The Application of Science to the Solution of Human Problems, Scott-Townsend (1992) ISBN 1-878465-03-1

Interviews

Notes
  1. Saxon 1989
  2. Sparks, Hogan & Linville 1991, pp. 130–132
  3. Carl, N.; Woodley of Menie, M. A. (2019-11-01). "A scientometric analysis of controversies in the field of intelligence research". Intelligence. 77: 101397. doi:10.1016/j.intell.2019.101397. ISSN 0160-2896.
  4. "Contributors to Proceedings of the I.R.E". Proceedings of the IRE. 40 (11): 1605–1612. 1952. doi:10.1109/JRPROC.1952.274003.
  5. Shurkin 2006, p. 5
  6. "Palo Alto History". www.paloaltohistory.org. Retrieved 2020-12-14. In Palo Alto, William’s temper improved little at first. But ignoring psychiatric recommendations for more socialization, his parents decided to home school William until age eight. Finally, feeling they were unable to keep him out of a school setting any longer, they sent him to the Homer Avenue School for two years, where his behavior improved dramatically --- he even earned an “A” in comportment in his first year.
  7. Hiltzik, Michael A. (December 2, 2001). "The Twisted Legacy of William Shockley". Los Angeles Times.
  8. Moll, John L. (1995). A Biographical Memoir of William Bradford Shockley (PDF). Washington, D.C.: National Academies Press.
  9. Shurkin 2006, pp. 38–39
  10. Shurkin 2006, p. 48
  11. Transistor - Innovation at Bell Labs Encyclopedia Britannica
  12. Broken Genius p. 65–67
  13. Shurkin 2006, p. 85
  14. Giangreco 1997, p. 568
  15. Newman, Robert P. (1998). "Hiroshima and the Trashing of Henry Stimson". The New England Quarterly. 71 (1): 27. doi:10.2307/366722. JSTOR 366722.
  16. The Artful Universe by John D. Barrow, Clarendon Press, Oxford, 1995, p. 239
  17. Brattain quoted in Crystal Fire p. 127
  18. Crystal Fire p.132
  19. CA 272437 "Electric current control mechanism", first filed in Canada on 22 October 1925
  20. Lilienfeld Archived October 2, 2006, at the Wayback Machine
  21. "William Shockley". IEEE Global History Network. IEEE. Retrieved 18 July 2011.
  22. Michael Riordan & Lillian Hoddeson (1998). Crystal fire: the invention of the transistor and the birth of the information age. ISBN 978-0-393-31851-7.
  23. Hoddeson, Lillian; Daitch, Vicki (2002). True genius: the life and science of John Bardeen : the only winner of two Nobel prizes in physics. Joseph Henry Press. ISBN 978-0-309-08408-6. Retrieved 30 December 2014. Lay summary – American Scientist (30 December 2014).
  24. Brittain 1984, p. 1695 "an observation that William Shockley interpreted as confirmation of his concept of that junction transistor"
  25. "Inventors of the transistor followed diverse paths after 1947 discovery". Associated press - Bangor Daily news. December 25, 1987. Retrieved May 6, 2012. 'mixture of cooperation and competition' and 'Shockley, eager to make his own contribution, said he kept some of his own work secret until "my hand was forced" in early 1948 by an advance reported by John Shive, another Bell Laboratories researcher'
  26. Broken Genius, p 121-122
  27. "1951 - First grown-junction transistors fabricated". Computer History Museum. 2007. Retrieved 3 July 2013.
  28. "Comstock Prize".
  29. ScienCentral, ScienCentral. "Bill Shockley, Part 3 of 3". www.pbs.org.
  30. Crystal Fire p. 278
  31. "Holding On". New York Times. April 6, 2008. Retrieved 2014-12-07. In 1955, the physicist William Shockley set up a semiconductor laboratory in Mountain View, partly to be near his mother in Palo Alto. ...
  32. "Two Views of Innovation, Colliding in Washington". New York Times. January 13, 2008. Retrieved 2014-12-07. The co-inventor of the transistor and the founder of the valley's first chip company, William Shockley, moved to Palo Alto, Calif., because his mother lived there. ...
  33. PBS program - American Experience (2012) 'Silicon Valley'
  34. Crystal Fire p. 247
  35. Goodheart, 2006 & "Fed up with their boss, eight lab workers walked off the job on this day in Mountain View, Calif. Their employer, William Shockley, had decided not to continue research into silicon-based semiconductors; frustrated, they decided to undertake the work on their own. The researchers — who would become known as 'the traitorous eight' — went on to invent the microprocessor (and to found Intel, among other companies).
  36. Gregory Gromov. "A legal bridge spanning 100 years: from the gold mines of El Dorado to the "golden" startups of Silicon Valley".
  37. Dawn Levy (22 October 2002). "William Shockley: still controversial, after all these years" (Press release). Stanford University. Archived from the original on 4 April 2005. Retrieved 14 June 2005.
  38. Crystal Fire p. 277
  39. BOYER, EDWARD J. (14 August 1989). "Controversial Nobel Laureate Shockley Dies". Los Angeles Times. Retrieved 11 May 2015.
  40. "Firing Line with William F. Buckley Jr.: Shockley's Thesis (Episode S0145, Recorded on June 10, 1974)". Retrieved 17 September 2017.
  41. Pearson, Roger (1992). Shockley on Eugenics and Race, pg. 15–49. Scott-Townsend Publishers. ISBN 1-878465-03-1
  42. Epps, Edgar G (February 1973). "Racism, Science, and the I.Q." Integrated Education. 11 (1): 35–44. doi:10.1080/0020486730110105.
  43. Kessler, Ronald. "Absent at the Creation; How one scientist made off with the biggest invention since the light bulb". Archived from the original on 2015-02-24.
  44. Shurkin 2006, pp. 259–260 "Essentially, the jury agreed that Witherspoon's column met the standards of defamation, but that by then, Shockley's reputation wasn't worth very much."
  45. Shurkin 2006, p. 286
  46. http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/shockley-w.pdf
  47. https://www.splcenter.org/fighting-hate/extremist-files/individual/william-shockley
  48. https://www.nytimes.com/1982/02/12/us/shockley-nobel-winner-files-for-senate-race-in-california.html
  49. "CA US Senate - D Primary". OurCampaigns. Retrieved 12 November 2019.
  50. A Science Odyssey: People and Discoveries: William Shockley PBS
  51. "Shockley's Ceiling". Mountain Project. Retrieved 2018-12-12.
  52. "Rock Climb The Ceiling, The Gunks". Mountain Project. Retrieved 2020-09-16.
  53. Crystal Fire p. 45
  54. Polly Morrice (2005-07-03). "The Genius Factory: Test-Tube Superbabies". The New York Times. Retrieved 2008-02-12.
  55. "William B. Shockley, 79, Creator of Transistor and Theory on Race". New York Times. 14 August 1989. Archived from the original on 2009-10-15. Retrieved 2007-07-21. He drew further scorn when he proposed financial rewards for the genetically disadvantaged if they volunteered for sterilization.CS1 maint: unfit URL (link)
  56. ScienCentral, Inc., and The American Institute of Physics (1999). "William Shockley (Part 3 of 3): Confusion over Credit". Retrieved 1 January 2015.CS1 maint: multiple names: authors list (link)
  57. "Comstock Prize in Physics". National Academy of Sciences. Archived from the original on 29 December 2010. Retrieved 13 February 2011.
  58. Editor, ÖGV. (2015). Wilhelm Exner Medal. Austrian Trade Association. ÖGV. Austria.
  59. "Google Patents assignee:(Shockley William)". patents.google.com. Retrieved 2020-12-12.
  60. Shockley, William (1971). "Models, Mathematics, and the Moral Obligation to Diagnose the Origin of Negro IQ Deficits". Review of Educational Research. 41 (4): 369–377. doi:10.2307/1169443. ISSN 0034-6543. JSTOR 1169443.
  61. Shockley, William (1971). "Negro IQ Deficit: Failure of a "Malicious Coincidence" Model Warrants New Research Proposals". Review of Educational Research. 41 (3): 227–248. doi:10.2307/1169529. ISSN 0034-6543. JSTOR 1169529.
  62. Shockley, Wiliam; Shockley, William (1972). "Dysgenics, Geneticity, Raceology: A Chalenge to the Intelectual Responsibility of Educators". The Phi Delta Kappan. 53 (5): 297–307. ISSN 0031-7217. JSTOR 20373194.
  63. Shockley, William (1972). "A Debate Challenge: Geneticity Is 80% for White Identical Twins' I.Q.'s". The Phi Delta Kappan. 53 (7): 415–419. ISSN 0031-7217. JSTOR 20373251.
  64. Shockley, William (1973). "Deviations from Hardy-Weinberg Frequencies Caused by Assortative Mating in Hybrid Populations". Proceedings of the National Academy of Sciences of the United States of America. 70 (3): 732–736. Bibcode:1973PNAS...70..732S. doi:10.1073/pnas.70.3.732. ISSN 0027-8424. JSTOR 62346. PMC 433346. PMID 4514986.

Other notes

References

Further reading
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