An internationally recognised expert on intelligence warns New Zealand children could get dumber in three or four generations unless women with higher education started producing more babies.
Otago University emeritus professor Dr Jim Flynn was commenting on census figures that show mothers without a higher education were the anchor of New Zealand's current fertility rate.
"Everyone knows if we only allowed short people to reproduce there would be a tendency in terms of genes for height to diminish. Intelligence is no different from other human traits," he told the Sunday Star-Times.
"A persistent genetic trend which lowered the genetic quality for brain physiology would have some effect eventually."
Statistics show women without tertiary qualifications who had reached their early 40s had produced 2.57 babies each.
In contrast, women with a higher education were producing just 1.85 babies each.
Dr Flynn said at 73 he was too old to worry about offending anyone.
Unplanned pregnancies by less educated women could be reduced, perhaps by future scientific advances.
"I do have faith in science, and science may give us something that renders conception impossible unless you take an antidote," he said.
"You could of course have a chemical in the water supply and have to take an antidote. If you had contraception made easier by progress, then every child is a wanted child."
Commissioner for Children Cindy Kiro said Dr Flynn was getting into "dangerous territory".
"Rather than talking about encouraging smart women to have babies and dumb women not to have babies, what we do need to do is make the commitment to good quality education."