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: