Free to Be You and Me never explicitly said that on the level of internal organs we’re all interchangeable, but to my mind it was implied.

So I set out to investigate Ms. Yamada’s assertion. Over the next few weeks, I asked Japanese students on our Tokyo campus if there were any differences between their intestines and mine. In a notebook, I jotted down the responses:

“Yes. Japanese intestines are longer.”

“Japanese intestines are much longer.”

“Never heard that.”

“Japanese intestines are exactly 1.5 times longer.”

“Who told you that?”

These initial answers were statistically similar to those I eventually gathered from a total of 120 students. Overall, 65 percent believed that Japanese intestines were longer. I heard the suspiciously precise “1.5” four times.

A junior on the men’s soccer team told me that because Japanese intestines are longer—sorry, there’s no delicate way to translate this—Japanese people excrete a higher volume of feces. The Japanese were so prolific in this way, he said, that one reason the Allies were victorious in World War II was that it was easy to spot hidden Japanese troops simply by searching for extra-high piles of human dung.

To be fair, he cautioned that he wasn’t 100% sure if that last part was true.

Thirty-five percent of the Japanese students I asked had never heard of the intestinal difference. But when I encountered students who said their intestines were indeed longer, I always asked if they knew why.

“We Japanese were traditionally an agricultural people,” one male explained. “Our ancestors didn’t eat much meat, so we evolved a longer intestine to digest the vegetables. You know, like how cows need multiple stomachs to digest roughage.”

I heard that answer a lot. There was something about it that seemed plausible, but I also detected an air of superiority in it. It positioned outsiders as carnivores—aggressive, lion-like hunters who were lazy most of the time (digesting meat). The Japanese, on the other hand, were grazers, always chewing, always working. Maybe I was just sensitive: Japan’s economic success had a way of making you feel inferior back then.

Certainly, though, the “agricultural people” explanation had holes. First of all, the identity of modern Japanese people’s ancestors is the great unanswered question of Japanese archaeology. (Much evidence points to the politically unwelcome conclusion that they came from the Korean peninsula.)

Second, although many non-Japanese eat a lot of meat, our ancestors—is it even possible to generalize about “our” ancestors?—probably ate less. And then there’s the idea that intestinal length varies inversely in proportion to carnivorousness, and that changes take place over just a few generations.

Or faster: One woman I spoke to hypothesized that when Japanese exchange students returned from a year living (and eating) in the United States, they would find that their intestines had shrunk.

Luckily I got involved with other things, and for a few years I didn’t think much about Japanese intestines.