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https://www.nytimes.com/books/first/w/wright-twins.html

http://www.personalityresearch.org/papers/haimowitz.html

http://www.medicaldaily.com/nature-vs-nurture-debate-50-year-twin-study-proves-it-takes-two-determine-human-334686

https://www.surveymonkey.com/r/?sm=rjQF3J2Awot0j5gAMEIIWw==

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