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.

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Every cell in your body holds an incredible 6 feet (1.8 m) of DNA. The same 6 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.

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 mice trained to fear a fruity odor passed sensitivity to this smell

on to 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, its 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 being reset.

This strange inheritance might even happen in humans. During the Dutch famine at the

end of WWII, children undernourished in the womb still carried epigenetic changes more

than 60 years later. And since these changes happen in the womb, they could have a huge

effect on our health as adults. In Överkalix, Sweden, boys who lived through

good harvests had sons and grandsons with higher rates of diabetes and heart disease,

while boys who lived through winter famines had healthier grandsons - they lived an average

of 32 years longer. Strangely, girls who 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’s developing, the cells that will make a grandchild are already present,

and can be exposed to 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’d 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 are written in our DNA

and it’s tough to totally rule out genetic changes or other factors even in the cases

we’ve seen. That’s the problem with studying complex animals whose lives are the product

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, diet, or environment, it wouldn’t

be totally surprising to find out our bodies are affected in ways we didn’t know about.

Epigenetics is a young science, and it’s reminding us we have a lot to learn about

what makes us who we are.

Stay curious.

Hey guys, so epignetics, pretty cool. And pretty weird. We just touched the tip of the

iceberg of this really interesting new field, and if you want to dig in deeper, there's

a ton of great links down in the description for you to check out. You know what else is

awesome? Physics! Crash Course Physics just launched last week, it's hosted by Dr. Shini

Somara, and like all of the Crash Courses, you're gonna love it. So head on over and

dig in. Stay curious!