 The most likely scenario then is that this rare variant was established in the islanders by a founder effect among a small initial colonising population, and was able to spread because of a selective advantage it conferred within that small group.Hence, in small populations under particular environmental conditions it may be feasible that the 'thrifty gene' idea is correct.It remains to be seen if rare variants that fill the gap in the missing heritability estimates are also 'thrifty genes' or if they are rare chance events sustained by drift, as implicated for the common variants currently linked to obesity and type 2 diabetes.