Hey Lilly, so did you know that twin studies have been conducted for more than 50 years but there is still some debate in terms of how much the variation is due to genetic or environmental factors. Identical twins are good for the "Age old Question" because "Twins" have been the main method for researching the genetic and environmental sources of variation between humans for a long time because of the availability that they give.
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I hope I helped you, and u can chat me if you want me to explain a little more for you :)
