[wwqrd]

How do you compare non identical twins to the general population? Aren’t twins, even non identical likely to share the same diet, the same environmental factors and maybe even the same viruses etc - all could be contributing factors?

[Retric]

Non identical twins are still siblings so they share a lot of DNA while also growing up in similar environments.

The huge difference between identical and non identical twins is suggestive of a very strong genetic component.