Sorry to bring this up on a weekend devoted to celebrating mothers, but you know all the things that have been wrong with young people for the past half-century? Mom’s fault.


I’ve reached this conclusion after an exhaustive study of an inadvertent historical record that has been left to us: the decades’ worth of sitcom mothers who have been caught on tape, as it were, giving dubious advice to children present and past.


At the start of this research, which consisted of watching whatever shows happened to be on TVLand-like channels in recent weeks or are in my DVD collection, I expected that modern-day mothers would be revealed to be shockingly lax, and they were. What I didn’t expect was to learn that their mothers, and their mothers’ mothers, were similarly irresponsible. And just as scientists have traced human lineage back to a mitochondrial Eve, the decline of motherhood can be traced to a single sitcom moment and a single sitcom matriarch. A momochondrial Margaret.


But let’s begin in the present. We all know instinctively that, though there are probably exceptions, in general kids today are immoral, nihilistic dunderheads. If American children are being outdone by young scholars in other countries, you need look no further than Mom to know why. Specifically, you need look no further than a recent episode of the ABC sitcom “Last Man Standing.”


Vanessa Baxter (Nancy Travis), the mother in the family, is playing Scrabble with two of her daughters when one of them tries to play T-H-A-N-G. “That’s not a word,” Vanessa says. The child who made the play stands by her “thang,” and the other child invites Vanessa to go look it up.


“Where’s the dictionary?” Vanessa asks.


“Upstairs,” she is told. To which this lax mom responds, “Fine; it’s a word.”


Mothers, it seems, can’t even be bothered to climb a flight of stairs in the interest of instilling good grammar in their offspring. No wonder American children are being outperformed academically all over the globe.


Why are our young people spending their time sexting instead of studying? Because for years Mom has been setting an appalling moral example. Take a 2006 episode of the CBS sitcom “Still Standing” called “Still Sweet.”


The family teenager wants a Sweet 16 party and is looking through a magazine with her mother, Judy (Jami Gertz), for dresses. They come across one that Judy describes as “just the kind of slutty thing Paris Hilton would wear.” Then she adds, “And I have just the shoes.”


From this we can conclude that mothers are responsible for the epidemic of scantily clad young people in the land. But where specifically did these kids lose their sense of modesty? Perhaps in a bar. Was that Lorelai (Lauren Graham) telling all sorts of lies to get her under-age daughter into an alcohol-serving establishment in a 2001 episode of “Gilmore Girls”? Yes, it was.


The line of questionable mothering extends into the last century, with ABC’s “Roseanne” perhaps the standout for its 221 episodes’ worth of turpitude. Let’s parse one small example, “Lovers’ Lane,” from the first season, in 1988. Roseanne (Roseanne Barr) has extorted information about her older daughter’s love interest from her younger daughter, Darlene. The child pleads with Mom not to tell big sister the source of the information.


“Oh, Honey, you know I’m smarter than that,” Roseanne tells Darlene. “I’ll just hold it over your head for the rest of your life.” How did all those manipulative bond traders and mortgage writers who destroyed the economy in 2008 become so unprincipled? In 1988, they, like Darlene, were impressionable kids, learning by example.


“Sure,” you’re thinking, “but that was the ’80s, a time of unrestrained wickedness. Go back a little further and you’ll hit the golden age of mothering: Carol Brady, Laura Petrie, Harriet Nelson. And June Cleaver! You can’t fault June Cleaver, can you?”


Actually, yes, I can. Look at “Beaver and Chuey,” a 1958 episode of “Leave It to Beaver.” Eddie Haskell has played a trick on the Beaver, and the Beav’s older brother is rushing out the door to exact revenge.


“Wally,” says June (Barbara Billingsley), “where are you going?”


He replies, “I’m going to go over and slug Eddie.”


To which this seminal, peerless mother says: “Wally! That’s no way to talk. This is Sunday.”


Wally grasps the moral relativism of the coming age instantly. He considers his mother’s input, then tells her, “Oh, yeah; I’ll wait till tomorrow and slug him in the cafeteria.”