The “island rule” is basic biology. Google it.
You made the assertion. Prove it. Don’t patronize me by talking down to me. If it’s basic biology it should be easy for you to find and shut me up, otherwise I’ll just assume that your talking through your hat.
I’ve always seen “the island rule” called “Foster’s Rule,” but I was educated outside the USA.
Foster’s Rule is a specialized application of the Reproduction Isolation Rule -— which states that happenstance genetic variation (e.g., color, size, or in this case, venom) will become exagerated over time in an genetically isolated population, especially if it gives the species an “edge” -— but also regardless, simply by re-ocurrance of an otherwise recessive trait.
Foster’s Rule applied Reproduction Isolation Rule to island populations.
The classic example was a study of a wild horse herd that was divided by a railroad fence.