Diets rich in red meat, seafood, and vegetables leave different chemical signals in fossil remains, which scientists measure to reveal details of what they ate.

How can we know what Kennewick Man ate?

Perhaps the most intriguing and puzzling finding about Kennewick Man was that he had a diet very rich in seafood—evidence perhaps that he lived a coastal life despite being buried in present-day Washington.

There were no fossil fish bones or fishing equipment found near him when he was discovered, so how can it be possible to tell what a man who lived 8,500 years ago, ate?

The answer comes from the power of atoms. And the knowledge that we are what we eat.

Atoms from the foods we consume become the building blocks for our cells, tissues and organs, and the atoms of carbon, nitrogen and oxygen—which make up a huge part of our body chemistry—come in slightly different forms called isotopes. Nitrogen, can for example nitrogen exist as ¹⁵N or ¹⁴N.

These two nitrogen isotopes appear equally likely in the flesh of animals, but only ¹⁴N is found in plants. This difference means that it's possible to spot the vegan in a room full of meat eaters, simply by measuring the nitrogen content of a hair sample.

This same principle can also distinguish where most of the carbon in our bodies comes from. ¹²C is found mostly from starchy foods in land, while ¹³C dominates inside marine animals.

Kennewick Man had a very high ¹³C count, and a low ¹⁵N count, which together suggest he ate relatively little meat, and lots and lots of seafood.

It's possible this marine diet reflects the idea that people colonizing North America were living coastal lives, navigating by boats, and coming in-land when needed.