Here’s one of my favorite science jokes. How do we know that diarrhea is hereditary? It’s in the jeans.

My warped sense of humor aside, what we thought we knew about genetics is changing, thanks to a bunch of New Zealand rabbits.

In 1978, some researchers wanted to study the effects of a high-fat diet on the heart.

They planned to check the blood cholesterol level, blood pressure, and heart rate of a group of test subjects, feed them a high-fat diet for a number of months, then check again to see what changes had occurred. Rather than ruin the health of a group of people, they ordered some male New Zealand white rabbits to experiment on.

When it comes to heart disease, the effects of diet on this breed of rabbit is similar to that of humans. Also, these rabbits were nearly identical genetically, so they were suitable test subjects.

The researchers expected that after several months on a high-fat diet, all the rabbits would have about the same increased levels of blood cholesterol, blood pressure, and heart rates.

After months on the high-fat diet, the rabbits were checked by the researchers. Most of the rabbits showed exactly what was expected: adverse effects from the diet. Most, but not all. Some of the rabbits had much better outcomes than the rest. By much better, I mean 60 percent better. These had lower blood cholesterol, lower blood pressure, and lower heart rate than their fellow bunnies.

The researchers were perplexed. Perhaps there was something wrong with the way they’d set up the study. They double checked everything. Yes, the rabbits were genetically very similar. Yes, the food they received was exactly the same. If there was no differences in the rabbits or the food, what did that leave?

The only possibility they could think of was the researchers themselves.

Checking which researcher had fed which rabbits, they found that the rabbits with better health outcomes had been fed by the same person. Each day while feeding her assigned rabbits, the woman hadn’t just given them food, she had talked to them, petted them, held them, and snuggled them, showing them kind affection.

The study was supposed to be about the effects of a high-fat diet on heart health, but this situation was too intriguing to ignore.

The researchers repeated the experiment with a new set of rabbits. Again, all were genetically similar. And again, all received the same high-fat diet. But some were talked to, held, and petted. After several months, the group that received kind interactions had significantly better test results than the others. The findings were so conclusive, a paper about the experiment was published in Science magazine.

In 2019, a doctor named Kelli Harding wrote a book called The Rabbit Effect, taking her title from that 1978 experiment. She makes a powerful case for the health benefits that can result from positive human interactions.

Kindness, it seems, is more important than what’s in the genes.

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