While in Sausalito Sunday, I watched as a sailboat race and a blimp glided over San Francisco Bay on the afternoon breezes.

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The lettering on the side of the blimp was difficult to read at a distance until I photographed the air ship, using a zoom lens. And even after studying the photograph, I wasn’t sure what was being promoted.

What was I to make of “23andMe.com personal genetics”? Or the slogan on the blimp’s nose: “Join the Research Revolution”?

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So I checked online. Turns out 23andMe.com is selling $399 “at-home DNA tests.” You supposedly can learn about everything from your risks of inherited ailments to your maternal and paternal ancestry, along with where on the globe where your strain of DNA is usually found.

Back in 1903, the remains of a man who had died approximately 9,000 years ago were found in Gough’s Cave in Cheddar Gorge, Somerset, England. For much of the next 93 years, “Cheddar Man,” as the remains came to be known, resided quietly in London’s Natural History Museum.

In 1944, however, the significance of DNA came to be understood, and in 1996, a researcher from Oxford University used one of Cheddar Man’s molars to check the old guy’s DNA. The researcher then had the bright idea to take DNA samples from 20 residents in the village of Cheddar, which is not far from the cave.

Apparently some families in southwest England really stay put — not just for generations but for millennia. Two Cheddar schoolchildren had exact DNA matches with Cheddar Man, and a teacher had a close match.

While many traits may be inherited from our ancestors via DNA, others can be passed down in unexpected ways. Here’s an example of a domestic accident that has affected four generations of my extended family.

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My mother Edith Mitchell, née Vokes, born in 1906, sits on the lap of her mother Harriet Vokes, née Wheeler, in Oshawa, Ontario, Canada.

Mom as a girl002_1When my grandmother was a girl in Canada back around 1880, she was slicing food in the kitchen one day when the knife slipped and cut deeply into a finger.

Bleeding profusely, she had to be rushed to a doctor.

The injury was sufficiently traumatic that when my mother (left) grew old enough to help in the kitchen, Grandmother repeatedly described the accident in warning my mother to be careful with kitchen knives.

I never met grandmother Vokes. She died in 1925, more than 18 years before I was born.

Mom with me c. 1945003_1 Mom emigrated to the United States in 1930, and my parents were living half a block from the Marina Green in San Francisco when I was born in 1943. As a result, many of my parents’ early photos of me were shot beside San Francisco Bay.

When I grew old enough to start helping Mom in the kitchen, she was so fixated on the danger of kitchen knives that she told me over and over how her own mother had injured herself by not cutting correctly.

The warning was drummed into my head to where even today at 65, whenever I slice food, I remember a finger’s getting cut — despite its happening 130 years ago in a foreign country to a person I never met.

100_2870_2_1_1When my stepdaughter Shaili Zappa, 16, was visiting from Guatemala last month, I told her this story and she was intrigued. (Photo of Shaili and me by Ana Gonzalez)

On Sunday, Shaili emailed me from Central America: “Every time I chop carrots, I remember the story!”

Think about it. A girl in Canada cut a finger with a kitchen knife during the 19th century, and although we are now in the 21st century, her direct and indirect descendants in the United States and Guatemala continue to wince. To my mind, that’s as remarkable as DNA.