Доказательства того, что моно- или дихориальность являются значимой характеристикой: M. Melnick et al., “The Effects of Chorion Type on Variation in IQ in the NCPP Twin Population,” Am J Hum Genetics 30 (1978): 425; N. Jacobs et al., “Heritability Estimates of Intelligence in Twins: Effect of Chorion Type,” Behav Genetics 31 (2001): 209; M. Melnick et al., “The Effects of Chorion Type on Variation in IQ in the NCPP Twin Population,” Am J Hum Genetics 30 (1978): 425; R. J. Rose et al., “Placentation Effects on Cognitive Resemblance of Adult Monozygotes,” in Twin Research 3: Epidemiological and Clinical Studies, ed. L. Gedda et al. (New York: Alan R. Liss, 1981), p. 35; K. Beekmans et al., “Relating Type of Placentation to Later Intellectual Development in Monozygotic (MZ) Twins (Abstract),” Behav Genetics 23 (1993): 547; M. Carlier et al., “Manual Performance and Laterality in Twins of Known Chorion Type,” Behav Genetics 26 (1996): 409. Смешанные результаты: L. Gutknecht et al. “Long-Term Effect of Placental Type on Anthropometrical and Psychological Traits Among Monozygotic Twins: A Follow Up Study,” Twin Res 2 (1999): 212; D. K. Sokol et al., “Intrapair Differences in Personality and Cognitive Ability Among Young Monozygotic Twins Distinguished by Chorion Type,” Behav Genetics 25 (1996): 457; A. C. Bogle et al., “Replication of Asymmetry of a-b Ridge Count and Behavioral Discordance in Monozygotic Twins,” Behav Genetics 24 (1994): 65; J. O. Davis et al., “Prenatal Development of Monozygotic Twins and Concordance for Schizophrenia,” Schizophrenia Bull 21 (1995): 357. Доказательство против: Y. M. Hur, “Effects of the Chorion Type on Prosocial Behavior in Young South Korean Twins,” Twin Res and Hum Genetics 10 (2007): 773; M. C. Wichers et al., “Chorion Type and Twin Similarity for Child Psychiatric Symptoms,” AGP 59 (2002): 562; P. Welch et al., “Placental Type and Bayley Mental Development Scores in 18 Month Old Twins,” in Twin Research: Psychology and Methodology, ed. L. Gedda et al. (New York: Alan R Liss, 1978), pp. 34–41. Цитата из: C. A. Prescott et al., “Chorion Type as a Possible Influence on the Results and Interpretation of Twin Study Data,” Twin Res 2 (1999): 244.