8 There is a moment in time. For Sir Thomas Browne’s views on deformity in Religio medici (1654) see his Works (1904) volume 1, pp.26–7. For the shift in opinion of monsters from wrath to wonders of God see Park and Daston (19?1). For William Harvey’s writings on generation see Anatomical Exercises on the generation of animals; to which are added, essays on parturition; on the membranes, and fluids of the uterus; and on conception (1650) in his Works (1965). The quote, however, is from the 1653 translation by Martin Llewellyn as given by Needham (1959) p.134.
10 It was, however, a contemporary of Harvey’s. For Bacon’s division of science see Bacon (1620, 2000) pp.14?–9 and 223–4. For an account of Renaissance collections of marvels see Daston and Park (199?) pp.255–301. Harvey, John Aubrey tells us, thought little of Bacon as either a philosopher or a writer, but Harvey espoused very Baconian sentiments when he wrote: ‘Nature is nowhere accustomed more openly to display her secret mysteries than in cases where she shows tracings of her workings apart from the beaten path.’
13 Most of these people have mutations. On-line Mendelian Inheritance in Man lists about a thousand genes that cause phenotypic variation, be it pathological or not (e.g. brown eyes).
16 If there is no such thing as a perfect or normal genome. The estimate of how many times each of the genome’s base-pairs have mutated in the last generation alone is given by Kruglyak and Nickerson (2001). The estimate of 65 per cent of genes as having polymorphisms applies to alleles defined by non-synonymous polymorphisms only. Conversely, my claim that most genes have an overwhelmingly common variant comes from the observation that 35 per cent of genes are monomorphic, and that in the known polymorphic ones, the minor alleles usually have a frequency below 5 per cent. Again, this applies to non-synonymous polymorphisms only (Cargill et al. 1999; Stephens et al. 2001).
18 Each embryo has about a hundred mutations. Eyre-Walker and Keightley (1999) estimate the rate of production of deleterious mutations in humans. Their estimates are consistent with those from Cargill et al. (1999) and Stephens et al. (2001) obtained by other means. Crow (2000) reviews the fitness effect of novel mutations.
CHAPTER II: A PERFECT JOIN
25 The Parodis arrived in Paris. Contemporary accounts of Ritta and Christina Parodi are given by Anon (1829 a; b; c); Saint-Ange (1830); Janin (1829) and Danerow (1830). Later accounts by Thompson (1930; 1996) p.84 and Bondeson (2000) pp.168–73.
26 The first cut exposed the ribcage. The major anatomical monograph on Ritta and Christina is Serres (1832). É. Geoffroy Saint-Hilaire (1829) considers the girls in a small paper and I. Geoffroy Saint-Hilaire (1832–37) in volume 3 pp. 161–74 of his synoptic teratology.
27 The oldest known depiction. The Anatolian statue, from the Catal Hüyük site, dates from around 6500 BC; the Australian rock carving from 3–4000 BC. For the Molionides brothers, and a more general discussion on con joined twins in ancient Greek art, science and myth, see Dasen (1997; 2002). For Renaissance teratologies see Paré (1573; 1982) and Boaistuau (1560; 2000) pp.134–7. For the Montaigne quote see Montaigne (1603; 1998), and for their intellectual context Daston and Park (1998) pp.205–7. The conflict between Duverney and his rivals is discussed by Fischer (1991) pp.71–4 and Wilson (1993) pp.150–9. For the intellectual context of preformationism and epigenesis see Needham (1959) chapters 3 and 4, and Pinto-Correia (1997).
32 What makes twins conjoin? Conjoined twins occur at a frequency of 1 in 100,000 live births; monozygotic separate twins occur at a frequency of 1 in 300 live births. For Aristotle on conjoined twins see The generation of animals in his Complete works volume 1 pp.1192–1996. See Friedman (1981) pp.180–1 on baptising conjoined twins.
33 Until recently, the origin of conjoined twins. For a typical medical embryology textbook account of conjoined twinning see Sadler (2000) p. 155. Although most conjoined twins seem to be monozygotic (they are nearly always of the same sex) there is at least one case that has been shown, by genetic tests, to be the result of a fusion between dizygotic embryos (Logroño et al. 1997). For the sex ratios of conjoined twins see Steinman (2001 a; b). Spencer (2000 a; b; 2001) gives a detailed critique of the fission model of conjoined twinning based on the geometry of the joins. See Martin (1880) pp. 153–69 for the evolution of theories of the causes of conjoined twins.
35 On the seventh day. For a description of early human embryogenesis see Beddington and Robertson (1999) and Sadler (2000).
37 In the spring of 1920. For the Hilda Mangold (nee Pröscholdt) paper see Spemann and Mangold (1924); for a translation and commentary see Willier and Oppenheimer (1964); for her biography see Hamburger (1988) and Fässler and Sander (1996).
39 For seventy years. For a brief history of the search for the organiser molecules see Gilbert (2002) A selective history of induction. http://zygote.swath-more.edu/. Spemann quoted in Gilbert (2000).
40 It would be tedious to recount. ‘Noggin’ is slang for ‘head’. For the initial identification of noggin (602991) see Lamb et al. (1993); for contemporary commentary see Baringa (1993); for a textbook survey of the organiser see Gilbert (2000) pp.303–38; and for a recent technical review see Beddington and Robertson (1999). The number of molecules involved in cell–cell communication includes both signalling molecules and their receptors (International Sequencing Consortium 2001). For the antagonism between BMP4 and chordin (603475) and noggin see Zimmerman et al. (1996) and Piccolo et al. (1996). For the noggin-defective mouse see McMahon et al. (1998); for the noggin and chordin double-defective mouse see Bachiller et al. (2000).
45 When Eng and Chang. The ‘two organiser’ theory is sometimes called the crowding model to distinguish it from the fission and fusion models (J.-F. Oostra, pers. comm.). Most fusion models postulate separate embryonic discs. My model is very similar to that of Hamburger (1947). It also seems similar to that of Spencer (2000 a; b; 2001) though she is ambiguous as to whether conjoined twins arise from one or two embryonic discs. Although, as stated, the vast majority of conjoined twins have a single amnion and placenta, there is apparently evidence that some have two amnions or even – truly strange this – two placentas. The ‘two organiser’ model would not apply to such twins. For chemical induction of conjoined twins (and mono-amnion monzygotic twins) see Kaufman and O’Shea (1978).