Uniquely twins.
el-Hai
J
J
D000375:Aging / Q000235:genetics*; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008910:Minnesota; D012042:Registries / Q000706:statistics & numerical data; D018433:Twin Studies as Topic; D014427:Twins / Q000235:genetics* / Q000523:psychology