Pigs that glow in the dark, chickens that grow without feathers,

and even goats that produce spider silk proteins.

But what really gets people riled up are genetically modified foods.

The prospect of eating somebody's science project turns the stomach

of those who aspire to eat so-called "whole" or "natural" foods.

But what does "genetically modified" mean anyways?

And how are those foods created?

To answer those questions we need to go back in time about 10,000 years.

That's when people first started domesticating animals

and cultivating plants for food.

By picking organisms with desirable traits and mating them together

over and over again, people were able to mold species

to meet their dietary needs.

The classic example is corn, which started out as a tropical grass

called Teosinthe with small, nearly inedible kernels.

Over thousands of years, ancient farmers in Mexico transformed the grass

into the delicious, starchy treat we like to eat today.

We now know those ancient farmers were manipulating

the DNA of the Teosinte plant.

As few as five changes to it's genome,

the long strands of DNA that encode for proteins

create the dramatic differences we see between Teosinthe

and corn.

Scientists call this process "artificial selection,"

and it's made all kinds of unappetising plants edible,

from wheat to rice to almonds and bananas.

What's different about modern genetically modified foods

is the speed and precision with which we can make changes.

Now, instead of selectively breeding for traits,

we can go directly to the DNA responsible, snip it out

and transplant it into newly developing plants and animals.

If these snippets come from the same species, scientists call the new

organism "cisgenic."

"Cis" means "the same."

But if the DNA comes from a completely different plant or animal,

scientists call the new organism "transgenic."

"Trans" means to cross.

Those florescent pigs, they glow green because they contain

a gene from a luminescent jellyfish.

And in the last 20 years, we've begun to see the food equivalent.

Corn that makes bacterial toxins poisonous to pests,

tomatoes that make the antifreeze proteins from fish,

and even cows that produce human milk.

So you may be wondering if this overt kind of manipulation is safe.

Well all of the GM foods currently on the market have been

thoroughly tested.

But the verdict is still out on some of the more exotic

transgenic pairings.

Personally, I'm waiting for a tomato that I can cut in the dark.

For Scientific American's Instant Egg Head,

I'm Eric Olson.