If you write enough columns, you begin to repeat yourself. And one of the facts that I’m continually forced to write when I cover nature documentaries is that humans and higher primates share more than 98 percent of their DNA. I’m not sure I want to share that much of anything with anyone. But it’s a fact that bears repeating. You and me and the average orangutan: We’re very, very, close.

Tonight’s “Nova” (7 p.m., PBS, check local listings), “Ape Genius,” offers a primate variation on the annoying old question: “If you’re so smart, how come you’re not rich?” If chimps, great apes, orangutans and bonobos have the building blocks of human intelligence, why haven’t they moved out of the trees and into the subdivision next door? What missing link are they missing?

The first half of this fascinating “Nova” makes the case that primates are very smart. We’re shown chimps and apes using tools and employing cooperative hunting strategies to hunt down smaller prey. Given their ability to imitate, use tools and work together, some argue that primates even have the rudiments of a culture.

In other tests, primates are shown to be smarter and learn faster than human 3-year-olds. Others demonstrate remarkable skill with words, letters and numbers.

The program’s second half demonstrates key human traits that primates don’t share and how some subtle variations may make all the difference. Apes show a strong tendency to imitate and to learn but absolutely no inclination to teach or to assume that other primates are capable of learning.

Unlike humans, or even dogs, apes don’t respond at all to pointing and seem incapable of comprehending a shared learning experience. One ape or chimp may learn to use a tool, but when he or she dies, that skill may be lost for generations or forever.

For reasons still not fully understood, primates don’t have the ability to create a body of shared knowledge to pass on to future generations.

Like most studies of primates, or any other animals, this provocative hour ends up being more about what makes us human than about what separates us from our hirsute cousins.

¢ For those of you who stopped paying attention, “The Janice Dickinson Modeling Agency” has ended its third season. The brash former supermodel moves on with a new show that is actually an old show imported from England called “Janice & Abbey” (10 p.m., Oxygen).

The Abbey involved is Abbey Clancy, the runner-up to the winner of Britain’s version of “Top Model.” Got that? Still care? You’re way ahead of me.

¢ “Frontline: Rules of Engagement” (8 p.m., PBS, check local listings) recalls the story of Haditha, Iraq, where more than two dozen civilians were killed in 2005. Interviews with civilians, military brass and survivors demonstrate that the story was far more complicated than first reported, when words like “war crimes” were used and eight Marines were charged with murder. Four have seen charges dropped, and for those still standing trial, the charges have been reduced from murder to manslaughter.

Tonight’s other highlights

¢ The 12 male talents sing to survive on “American Idol” (7 p.m., Fox).

¢ Mike travels to New York and learns if you can clean it there, you can clean it anywhere on “Dirty Jobs” (8 p.m., Discovery).

¢ Alex doubts therapy really works on “In Treatment” (8:30 p.m., HBO).

¢ Doubts about the Cheyenne regime fester on “Jericho” (9 p.m., CBS).