We can inherit a lot from our parents hair, and eye color, height.

But we can't inherit everything.

Because some biological traits are acquired during our lifetime.

The only way to transmit biological information between generations is in the letters of our DNA.

But what if it's not that simple?

What if our environment and our experiences can be passed on to our children and grandchildren?

Inheritance is turning out to be much weirder than we think.

[music playing] Every cell in your body holds an incredible six feet of DNA, the same six feet of DNA, each holding identical genetic instructions.

Yet when skin cells regenerate every day the new ones somehow know to become skin cells, not bone or muscle.

Something beyond just DNA influences their destiny.

This is what scientists call epigenetics, differences in traits that aren't due to changes in the DNA sequence.

When it's wrapped up inside the cell tiny chemical flags on the DNA, or the proteins it's coiled around, signal the cell to turn certain genes on or off.

So they make just the right machinery to do their job.

Now these chemical flags are rewritten every day as organisms adapt to new environments.

But scientists are seeing something strange.

Some of these changes can be passed on to the next generation.

Mice fed high fat diets get fat, unsurprisingly, thanks to changes in the chemical flags on their DNA.

But female children of these obese mice-- even though they were taken away and raised by normal sized mothers-- still ended up 20% fatter than mice from skinny parents.

In another example, male nice trained to fear a fruity odor passed sensitivity to this smell onto their children and grandchildren, even though their offspring had never been exposed to it.

If this sounds a lot like what that guy Lamarck was talking about, well you're not wrong.

Before Darwin many scientists thought acquired traits could be passed on.

But natural selection proved that wrong.

But even so, scientists have since seen cases in species from flowers to fruit flies where traits are passed on to children and grandchildren without changing the DNA sequence.

There's just one catch.

This shouldn't be possible.

Just hours after an embryo is conceived it's chemical flags are erased.

So all the cell types in the new body can be built from a blank slate.

And cells destined to become sperm and eggs get erased a second time.

At least that's what scientists thought.

For epigenetic inheritance to work some flags must sneak through without be reset.

This strange inheritance might even happen in humans.

During the Dutch famine at the end of World War II children undernourished in the womb still carried epigenetic changes more than 60 years later.

And since these changes happened in the womb, they could have a huge effect on our health as adults.

In Overkalix, Sweden, boys who would live through good harvests had sons and grandsons with higher rates of diabetes and heart disease.

While boys who had lived through winter famines had healthier grandsons.

They lived an average of 32 years longer.

Strangely, girls who had lived through swings of feast and famine had granddaughters with higher rates of heart disease.

That's confusing.

But human lives aren't easily controlled lab studies.

And that's why some scientists doubt this new kind of inheritance.

Epigenetic changes can definitely happen between one or two generations, but for a trait to have an effect on evolution it has to endure for dozens of generations.

When a baby is developing the cells that will make a grandchild are already present and can be exposed to the same environment as the grandmother.

That's not inheritance as much as super-duper early exposure.

For epigenetic changes to be truly inherited they have to be rewritten in every generation.

We have to see them in great-grandchildren and beyond.

And that's just not clear yet.

Even so, the vast majority of traits that make us who we are in our DNA.

And it's tough to totally rule out genetic changes or other factors, even in the cases that we've seen.

That's the problem with studying complex animals whose lives are the products of thousands of genes in trillions of cells.

There's a lot going on here.

But since many of our diseases are linked to stress, and diet, or environment it wouldn't be totally surprising to find out that our bodies are affected in ways that we didn't know about.

Epigenetics is a young science.

And it's reminding us that we have a lot to learn about what makes us who we are.

Stay curious.