On Nov. 22, 1965, a despondent, mentally ill woman named Maggie Young took her four daughters, one by one, into the bathtub of her Hawaii home and drowned them. The oldest was 5; the youngest, just eight months.

Then she yanked her 8-year-old son from school, brought him home and killed him the same way. She placed all the bodies, wet and nude, on twin beds  the girls on one, the boy alone on another.

Young immediately confessed, and after she was found unfit to stand trial, was committed to a state hospital. About six months later, she escaped to a chicken shed on the hospital grounds and hanged herself.

Andrea Yates was born that same year.

As we all know by now, her tale is eerily resonant: Five children. Similar ages. Overwhelmed, psychotic mother. Bathtub drownings. Beds turned into mortuary tables.

The outcome, however, is not. Thirty-five years ago, psychiatrists determined that Maggie Young was “diseased and deranged” and unable to participate in the legal process. In Houston last week, jurors took only a few hours to find Yates guilty of capital murder and Friday quickly sentenced her to life in prison without parole for at least 40 years.

What have we learned in the intervening decades? Only that our justice system is biased and inconsistent in the conflicting way it treats those who are sick enough  or evil enough  to kill their own children. Especially if the murderers are mothers.

Given the uncompromising severity of Texas law, and the Hobson’s choice between death or life behind bars, the jurors did their job well. They wisely spared Yates the fate of the two other Texas women who sit on death row for killing their children.

But there’s little sense of closure or satisfaction here. Andrea Yates deserves treatment along with punishment. Her trial offered a glimpse into a complicated, gruesome landscape, a dark corner of human behavior that has always existed, always defies explanation, and never ceases to horrify.

This is not a pretty topic. Women commit about half of all parental murders in the United States. That revelation alone gives me the chills; the details invite nightmares.

A mother killing her child is nature upended, a reversal of instinct, a violent challenge to the natural order of things. That so many of these crimes are highly physical  drowning, shaking, strangulation, beating  intensifies our repulsion. The very hands that nursed and soothed can batter and kill.

“We expect that women are going to be super-protectors and men are going to, well, provide,” says Cheryl Meyer, psychology professor at Wright State University in Ohio and co-author of “Mothers Who Kill Their Children.”

And when women harm rather than protect, we declare that they must be very ill  depressed, isolated, psychotic, abused. “Perhaps it comforts us to believe that anyone who violates the sacred mother-child bond is simply crazy; it would be unimaginable if these mothers were making rational criminal choices,” writes Dahlia Lithwick for Slate.com.

This concept is codified in Britain through the Infanticide Act of 1922, which applies to all women who kill their children within the first 12 months of life. Based on the belief  there’s little scientific evidence  that these killings are all due to post-partum depression, the law has virtually decriminalized them.

America doesn’t work that way, and I don’t imagine that it ever will. As the Andrea Yates case shows, we are far more conflicted about the sources of blame and responsibility for these horrendous crimes.

Juries are generally loath to hand down murder convictions for mothers accused of killing their own children. Men who do so are much more likely to be sentenced to prison or executed and much less likely to use mental illness as a mitigating circumstance (or an excuse).

And yet there are at least eight women convicted of that crime and awaiting execution in Texas, California, Florida and Arizona. A ninth is in Pennsylvania: Michelle Sue Tharp of Burgettstown was sentenced to death in 2000 for the murder of her 7-year-old daughter. Tharp starved the child to death, then dumped her emaciated body on a rural road in West Virginia.

But if women who kill are treated more leniently in some states, they are often held to a higher standard when their partner did the killing. In her book, Meyer identified women who were convicted and sentenced to jail even if they weren’t home when the crime occurred.

The Illinois Supreme Court, for instance, upheld murder convictions of two women whose boyfriends killed their children, charging that because the women allowed the abuse to occur they were responsible for the deaths. One of the women wasn’t present when the child was killed; the other couldn’t see the signs of abuse because she was legally blind. No matter. Thirty to 60 years in jail.

Compare that with the treatment of Andrea Yates’ husband, Russell, who knew of his wife’s mental illness, knew she was suicidal, knew she shouldn’t have had another baby and had to know that she shouldn’t be left alone without support. He was not charged.

Andrea Yates failed her children. Russell Yates failed her. Their village  family, church, friends, neighbors  failed them both.

And our system of justice too often fails to recognize the inconsistencies and biases with which we treat this most horrific of crimes.

 Jane R. Eisner is a columnist for Philadelphia Inquirer. Her e-mail address is jeisner@phillynews.com.