the orange-cherry-almondy scent of the chemical acetophenone with a painful electric shock,

lab rats quickly learned to fear it. Along the way, extra neurons sprouted in their noses

and in the smell-processing center of their brains, making them super-sensitive to the

scent.

This result isn’t shocking. What is surprising is that the rats' pups – and their pups'

pups – were also startled by the smell of acetophenone and had the same extra neurons

as their fathers, despite never having been introduced to either their dads or the fruity

scent before.

But how could the pups have inherited something their fathers learned? Basic genetics tells

us that only DNA gets passed along to offspring; characteristics like memories, scars, or giant

muscles, can’t get passed on since acquiring them doesn’t alter the genetic code. But

it turns out that instilling fear in the rats did trigger genetic changes - not in the DNA

sequence itself, but instead, in how that code was read and used in the rats’ bodies.

In every cell, biological machinery constantly translates DNA into the proteins needed to

carry out vital processes. Chemical switches attached to the DNA turn genes on and off

or up and down, telling the machinery which proteins to produce and in what quantities.

These switches, called “epigenetic tags,” are why a kidney cell looks and acts differently

than a skin or nerve cell, even though the two cells’ DNA is identical.

But the switches in any one cell aren’t set in stone: teaching those rats to fear

that fruity smell switched one of their smell-sensing gene into overdrive. Researchers don’t know

all the places in the rats’ bodies where this switch got flipped, but they know it

happened in one key set of cells: the rats’ sperm cells, which would one day pass along

this tweaked genetic material, making the next generation of rats super-sensitive to

acetophenone.

Rodents aren’t the only creatures demonstrating this weird type of inheritance. In Överkalix,

Sweden, boys who suffered through tough winter famines went onto have super-healthy sons,

with extremely low risks of heart disease and diabetes. And their sons’ sons had the

same excellent health, living an unbelievable 32 years longer, on average, than the grandsons

of boys who hadn’t gone hungry.

To be clear, this does not mean we should start starving our kids for the benefit of

future generations – scientists don’t even know yet exactly which switches the Swedish

famines flipped. While we have been able to connect specific epigenetic changes to health

effects in mice, we’re a long way off from being able to make those connections in humans.

That may sound like a bummer, but it’s mostly because we humans don’t live in the well-controlled

environment of a laboratory. And for that, we should be grateful.