Mr. Hawthorne went on gamely. “Learned behavior, no. But a lot of behavior is hereditary,” he said.

While he does acknowledge that when it comes to such highly trainable creatures as dogs, it’s pretty difficult to know where nature ends and nurture begins, he said that in the case of his dogs, the ambiguities have nothing on the essential Missy-ness of the clones.

Image HOWLING TIME Mira, left, and MissyToo appear to be a tough audience for Lou Hawthorne, who had them cloned from the DNA of his mothers dog. Credit... Heidi Schumann for The New York Times

“The girls love to run after each other,” he said pointing at the dogs in the distance. “You see the speed and athleticism? That’s part of what made me want to do this. There are dogs that are faster on a straightaway, but I’d never seen a dog make turns like this until Missy.”

Mr. Hawthorne sees himself as a cultivator of prodigious talent  from the clones to his team of scientists in South Korea to his 8-year-old son, Skye, who had accompanied him and the dogs on the hike. Skye is in third grade but is already studying high school algebra. Mr. Hawthorne brought along a notebook with a handful of quadratic-equation problems, in case his son got restless.

Last spring, Skye completed a science project, “Cloning Grandma’s Dog” that included a behavioral comparison chart. Among other findings, the study concluded that Mira shares Missy’s fondness for broccoli and “lots of snuggles”  both dogs scored five out of five points in these categories, in addition to the one for “likes long walks.” (“Most dogs do,” Skye noted under “comments.”) Two key matters of variance were “Jumps into cars” (“Clone still learning which car is ours”) and “Hates camera flash” (“Clone did not respond to standard flash”).

Ultimately, Skye determined that Mira looked a lot like Missy but that their behavior was only 77 percent similar. “But that was April,” Mr. Hawthorne said. “I think they’re a lot more similar now.”

LIVING with a clone, Mr. Hawthorne claims, is a lot like living with the original dog. “It’s totally as if I’ve got Missy in my house, once you get over the ‘wow’ factor,” he said. He and Mira and Skye inhabit a two-story “1950s futurist house” built into a hill in Mill Valley (Mr. Hawthorne is divorced and shares custody of his son with his ex-wife  “an excellent genetic donor, by the way,” he said of her). At night, he said, Mira “puts Skye to bed,” which means she walks with him to his room and ascends the stairs of his loft bed with him, waiting to be told “Good night” before she leaves. Mira is an outdoor dog, as Missy was, and sleeps on the front steps.

And who says goodnight to Mira’s fellow clone, MissyToo? Mr. Hawthorne gave her to his mother, Joan Hawthorne, who still misses the original Missy. But she has yet to take a liking to Missy’s progeny, and the dog has lived primarily with paid “handlers” in the Mill Valley pied-à-terre of her longtime companion, John Sperling.