Key Points:

Okay, some of you are starting to worry me. The more excitable among you seem to have got a little carried away with the idea of forcing sterilisation on certain types in society - the poor, the intellectually challenged, the mentally ill, the bad, the ugly and the deeply irritating. Basically, just about anyone who ticks you off. (I'm sorry, but were you perhaps not nurtured as a child?)

Seriously now. If there's one thing the recent advances in brain development research (mentioned in last week's column) have done, it's to render obsolete the old nature vs nurture argument - and the idea that intellectual capacity is determined by genes alone. Or that high IQs are not to be found in the children of the poor.

The evidence says otherwise.

As Chicago University economics professor James Heckman has noted, "Evidence from epigenetics suggests that the genes vs environment distinction that is so much in vogue in popular discussions of inequality is obsolete, as is the practice of additively partitioning outcomes due to 'nature' or 'nurture' that is common in many papers in economics. An extensive recent literature suggests that gene-environment interactions are central to explaining human and animal development."

Which means, critically, that there is much, much more we can do to improve the chances of every child growing up smarter, healthier, more emotionally balanced, and - importantly for the economists - productive.

So why don't we? How come it's so hard to get the message out?

Most of us get there without all the science, of course. I didn't need peer-reviewed studies to tell me that talking and reading to my children from birth was better for their brains than watching TV. But I would've liked to know how important play was, too.

Still, I had my mum, who could coo and sing and cuddle, and a whole lot else besides, when I wasn't up to it.

For those who weren't lucky enough to have their mothers around, there was Plunket.

We seemed to understand once that all parents needed support rearing their children. When Plunket was set up in 1907 to "help the mothers and save the babies", its goal was to improve the survival and fitness of future citizens in the interests of "national efficiency".

According to Auckland academic Linda Bryder, author of A Voice for Mothers: The Plunket Society and Infant Welfare 1907-2000, "The diagnosis of the problem and the solutions put forward were the same everywhere: mothers were ignorant of the correct methods of child rearing and needed to be educated."

That played a significant part in New Zealand's infant mortality dropping from 40.57 per 1000 live births in 1906 to 9.5 by 1936, then the lowest in the world.

We know a lot more now about what is and isn't good for children. But we seem to have no mechanism in place to deliver the message. Funding cuts since the 1980s have weakened institutions like Plunket, just when they've been needed most.

It doesn't help that any discussion about parenting tends to get bogged down in ideology and politics.

Which matters more, for example, parenting or income?

Heckman cites a study in which an American Indian community "enriched by the opening of a casino, showed substantial improvements in baseline measures of disruptive behaviour of their children... Parental supervision of children improved, and there was greater parental engagement".

In this case, "income improved parenting, but it was parenting that reduced disruptive behaviour".

Education makes a difference. The children of more educated women do better than the children of the less educated, but then they tend to marry later, have more resources at their disposal, fewer children, and have the kind of rich child-rearing environments that make a difference in vocabulary and IQ.

Policy matters, too. Integrated, universal, high quality early-childhood programmes reach the greatest number of children and don't stigmatise families.

Making sure poorer communities have more early childhood centres, libraries, swimming pools and parks than liquor stores matters, too.

The new Minister of Social Development, Paula Bennett, wants a debate on whether mothers are being pushed back to work too soon after having children.

What is there to debate? It's clear that many mothers feel pressured by their financial circumstances and future career prospects to return to work sooner than might be good for them or their babies. Equally clearly, there are some women who can't get out of the nursery fast enough.

The more important question for Bennett ought to be how public policy is contributing to a lack of choice for some mothers, and how it might support those who have neither the choice nor the resources.