“The pug,” wrote the late humorist Margo Kaufman, “is living proof that God has a sense of humor.” But the folks at “Explorer” (7 p.m., National Geographic) may beg to differ.

The hour-long documentary “Science of Dogs” argues that many of the traits we associate with our four-legged companions have come about not through divine design but through careful breeding and inbreeding. Dogs, it seems, are not just man’s best friends, but man’s own science project. Like orchid cultivators, dog breeders use genetics and eugenics to arrive at particular canine attributes.

It’s remarkable to note that every dog breed, from the tiny Chihuahua to the Great Dane, descend from wolves. But it’s mind-boggling to note that all domesticated dogs share more than 99.8 percent of their DNA. A small change in a single gene is responsible for the difference in size between the biggest dog and the smallest.

Traits peculiar to dog genetics explain the rapid evolutionary changes in canines. It’s one thing to go from wolf to poodle in a few thousand years. But many dog breeds have emerged in just the past two centuries.

“Science” looks at the Dogo Argentino, a breed designed over the past 25 years for the single purpose of hunting down wild boars. A Soviet expert mated several breeds of hunting dogs with wild jackals to arrive at the Sulimov, a trainable bomb-sniffer without compare. Its sensitive nose can detect 12 different chemical compounds used in explosives.

Of course, all of this genetic tinkering has had some side effects. The pressure to maintain breed standards established in the Victorian era has resulted in a shallow gene pool for some particular dog varieties. The gene responsible for a Dalmatian’s unique coat has been linked to a mutation causing deafness. One purebred dog in four has some kind of genetic disorder.

“Science” also shows how thousands of years of human-canine interaction have changed the very nature of dogs. In one experiment after another, wolves try to solve problems by themselves or with their wolf pack. Given the same obstacle, a dog will quickly turn to its human master, or pack leader, for help. Questions remain about the origins of the deep affection between humans and dogs. Are dogs bred to love us? Or is that explained by a higher power?

Tonight’s other highlights

¢ Cat Deeley hosts the final four on “So You Think You Can Dance” (7 p.m., Fox).

¢ The final six make jokes on “Last Comic Standing” (8 p.m., NBC).

¢ “NASCAR in Primetime” (8 p.m., ABC) offers a look at the preparation for a race and conversations with several drivers.

¢ Viewers come up with new urban legends to debunk on “MythBusters” (8 p.m., Discovery).

¢ Scheduled on “Dateline” (9 p.m., NBC): the search for a vanished polo player.

¢ The group discovers they are under watch on “The Nine” (9 p.m., ABC).

¢ “Taboo: Signs of Identity” (9 p.m., National Geographic) looks at cultures and subcultures around the world that use branding, scaring and beatings as rites of passage and initiation.

¢ The girl from the restaurant (Gina Gershon) lingers in Tommy’s mind on “Rescue Me” (9 p.m., FX).

¢ A burger with a difference on “Top Chef” (9 p.m., Bravo).

¢ Posh real estate becomes the backdrop for petulant self-involvement on “Newport Harbor: The Real Orange County” (9:30 p.m., MTV).

¢ The quarterback job seems up for grabs on “Hard Knocks: Training Camp with the Kansas City Chiefs” (9 p.m., HBO).