>> When the food gets tough ...

the tough get chewing ...

and often with teeth adapted through evolution to handle the demanding cuisine.

That's the finding of scientists from George Washington University and the National Institute of Standards and Technology

who report that different types of apes use these special teeth to chew foods

that become the fare when their usual staples are scarce.

>> Chimpanzees, gorillas, and orangutans all prefer the same foods, and these foods are soft ripe fruits.

But they don't actually have similar tooth morphology.

They have some significant differences in their teeth.

Based on observations in the wild, we had some ideas as to why this might be, but we really had to come to NIST

and do some experiments here to gather the data necessary to support those ideas.

>> For chimps, gorillas and orangutans ...

the usual daily menu means fruit.

But sometimes fruit is in short supply ...

and that's when apes have to look for what scientists call "fallback foods."

Gorillas go for leaves and tree bark ...

while orangutans opt for nuts and seeds.

Chimpanzees simply hit the road to gather the fruit they can't find at home.

Constantino and his team of anthropologists hypothesized that gorillas have evolved broader back teeth for the purpose

of chewing leaves and bark, which are soft but fibery tough.

Orangutans ...

on the other hand ...

would have developed molars with thicker enamel to withstand the stress of crunching hard seeds.

>> It makes sense if you think about it because when times are hard, that's when your survival tools are most important.

If you don't have the teeth that are able to chew through your fallback foods, then you're not going to be able to survive

until a period when you can get those easier-to-access foods.

And if you can't survive through that period, then you obviously can't pass on your genes to the next generation.

>> To test these ideas ...

the GWU researchers asked James Lee, a NIST materials expert, for help.

>> In our laboratory, we perform fracture experiments on human teeth, and from these experiments,

we develop models that can be applied to other animals.

We thought this technique could shed some light on how primate teeth may have formed.

>> The NIST data support the GWU hypothesis that apes developed their special teeth for fallback foods.

In addition ...

the researchers say they may have evidence showing that fallback foods have influenced the form of ape jaws and skulls.

And their results could have important implications for the apes of today.

>> [Sound of apes] So, if humanity is serious about protecting apes, and conserving them,

then we need to protect not only the fruit trees that these animals rely on for most of the year, but also the fallback foods

that they rely when times are particularly tough.

Our research shows just how important and influential these fallback foods are.

Apes have evolved over millions of years the tools needed to access these foods,

but they still have to be able to find these foods in the first place.

[Silence]