Identical Twin Studies and Evolutionary Psychology
by Dr Beetle   
Twin studies are widely used in evolutionary psychology as evidence of genetic determination in behaviour. Identical twins share 100% of their DNA. They look similar, and arise when one egg splits to give two eggs with the same DNA (monozygotic). Fraternal twins look less alike, and may also be of different sex. Although they develop in the same womb, they arose from two separate eggs so share just 50% of their DNA (dizygotic). Identical twins, even when reared apart, can have an uncanny similarity in behaviour, more so than for similarly treated fraternal twins. Surely proof that genes rule. But for Dr Beetle, there is another way to understand the results. The similarities are more likely to be due to learning and shared environmental experiences. There are four major assumptions that undermine the evolutionary psychology approach to twin studies: