![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Selfhood, and identical twins, 157-160
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Sex. See Homosexuality; Love life of twins
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Shafran, Robert, 36-37, 38-39
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Shared vs . non-shared environment, 62, 140-142, 147-148
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Shields, James, 67
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Siamese twins, 90, 118-119
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Sigmundson, H. Keith, 116
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Skinner, B.F., 23-24, 30
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Social attitudes, heritability of, 123, 147
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Social programs, views of need, 9-10, 148
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Southern California Twin Project, 128
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Soviet Union, and twin studies, 15-16
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![](/files/03/02/28/f030228/public/bd014e5cf10977d319edfaab72ea3d1a.gif) | Spencer, Herbert, 14
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