CARETAKER THWARTS UNDERTAKER; STUDY FINDS AT-HOME PARENTS LIVE LONGER.

Byline: Alex Roth Daily News Staff Writer

A longevity study released Monday might make sense to anyone with an obnoxious boss but surprise the parent of a typically rambunctious 2-year-old.

Based on studies of apes, monkeys and humans, the research shows that a parent who assumes primary responsibility in child rearing will tend to outlive his or her spouse, California Institute of Technology researchers announced.

But a word of caution for humans: It probably doesn't matter whether a wife goes to work and the husband stays home with the kids. The man pretty much is doomed by genetics, the study suggests.

``Natural selection will evolve mechanisms that protect the caretaking sex relative to the other sex,'' said John Allman, a Caltech biology professor who is lead author of the study, published in this month's Proceedings of the National Academy of Science.

Natural selection has ensured a long life for the primary caregiver simply to ensure the infant's survival, he said.

In a study of 10 primate species, the research shows that the infant's primary caregiver lives ``significantly'' longer than the male. This is true in some species when the male is the caregiver, as evidenced by South America's titi monkeys. Male titis outlive their mates by 20 percent, the researchers said.

Among humans, women's lives are 8 percent to 10 percent longer than men's, according to Allman. His human research was based on Swedish census data, which goes back as far as the 18th century, he said. He noted that women outlived men even in 1780, when childbirth was a leading cause of death among females.

While genetics involved in the child-rearing theory seem the single most logical explanation, other factors may also play a role, Allman said.

``Risk-taking in males and estrogen in females are probably factors, and there may even be a beneficial hormonal or chemical change that occurs through extending care to another,'' Allman said.

Stay-at-home parents also insist the lack of stress has to count for something in the life span department. Given the realities of 9-to-5 employment, stay-at-home parents say, it's nice to know the only childish behavior you have to deal with is your children's.

``I jokingly tell people I plan to live to be 100 years old,'' said Casey Spencer, 46, of Glendale, who runs Dad-to-Dad of Los Angeles, a group of stay-at-home fathers.

Several years ago, Spencer quit his job as a professional photographer to take care of his 3-year-old daughter full-time. His wife is a theme park executive. ``My wife is the high-stress one,'' he said. ``She puts in more hours, she probably has higher blood pressure. I fear that I will outlive her.''

Not that raising a child full-time doesn't have life-shortening annoyances.

``I'm surprised they don't live shorter (than their spouses),'' said Barry Reszel of Libertyville, Ill., who edits the At-Home Dad Handbook.

Reszel was kidding. Sort of.

``I'm glad I don't stay at home,'' said Bernice Stewart, a 46-year-old Woodland Hills secretary who puts her 6-year-old girl in child care. ``If I did I'd probably drop dead in five years.''