03/18/2010 05:12 am ET | Updated Nov 17, 2011

A New Review: How Your Early Environment Shaped You

To twist an old quip: Theories come and theories go, the environment remains. The first half of the 20th century was a big bang for the idea that every child was born a blank slate to be shaped by family and social environments. During the second half of the 20th century, the obtuse pendulum of fashion swung in the other direction, until everyone, down to every newspaper editor and science writer, shouted at the public that no, it's not environment but genes and heredity that shaped people. Now the pendulum is swinging the other way (yes, I wrote a book about it), but it may take certain media science pundits another decade before they realize the goose is running away from them at high speed.

Meanwhile, science marches on. Most biological scientists don't give a hoot about the contents of newspapers or sophomoric books hawking genes as destiny: they're too busy going blind reading journals and looking through microscopes. It's a fact that the evidence has been piling up for decades that from conception through about the age of twelve or fifteen much of the brain is indeed a blank slate, and this time we know more about the molecular and neuroanatomical basis of what is or is not on the slate than we did fifty or sixty years ago. We have indeed moved forward, and it's regrettable that as usual it takes too long for progress in science to dribble through media filters into the public imagination.

Ian Weaver, a developmental biologist at the Hospital for Sick Children in Toronto, gives us a new review of what's been happening to revive the importance of the environment in shaping human development.(1) He makes the following points:

1) The human endocrine system is closely regulated by the brain, a neuroendocrine regulation that governs physiological regulatory mechanisms essential for life: metabolism, immune responses, and organ function. One of the key questions in current developmental biology and medicine is how stress and environmental adaptation impact this regulation to produce harm to body and mind.

2) The current new view is that a switch from protection to damage occurs when certain people (fetuses, children, or adults) have particular vulnerabilities to adverse environmental conditions.

3) The general idea is that various environmental stresses during life--such as childhood abuse, neglect, poverty, and poor nutrition--are associated with the emergence of mental and physical illness--such as anxiety, mood disorders, poor impulse control, psychosis, and drug abuse--and increased risk of common metabolic and cardiovascular diseases in later life.

Weaver summarizes our current molecular understanding of how early environment influences brain development--an influence that persists through life. He highlights recent evidence from animal studies suggesting that early maternal postnatal care establishes varied and stable individual types (phenotypes) in offspring. The mechanism is apparently epigenetic modifications of genes expressed in the brain, modifications that shape the response to stress of the neuroendocrine system and behavior throughout life.

What this is all about in plain language is a revision of the simplistic idea that there is no blank slate at all and that human individual destiny is determined by inherited genes. Too many people love the idea of genetic destiny for political reasons: it justifies nepotism and socioeconomic inequalities. In fact, in our frontal lobes, the most important parts of the human brain, the parts most recently formed by Darwinian evolution, it takes twelve or even fifteen years after birth to get the wiring done--and how you get wired up depends greatly on where you are and what's around you and the daily stresses of your existence. Truly, no matter the gene-hawking in newspapers and magazines, the idea of genetic destiny needs to be put in a trashcan with a secure cover.

Note (1): Weaver, I. C. (2009). Shaping adult phenotypes through early life environments. Birth Defects Res C Embryo Today. Dec;87(4):314-26.