Not that long ago, delaying motherhood to pursue a career or an education was viewed with skepticism or scorn, if not outright hostility. Concerned grandmothers were likely to take an ambitious daughter aside and insinuate that, if she put off babies for her work or an advanced degree, her ovaries might just shrivel up. In the early part of this century, physicians agitated that delaying motherhood could lead to all sorts of nervous ailments, including false or hysteric pregnancies. Teddy Roosevelt singled out mothers of big families as the ultimate role models for young women, claiming in one address that any woman who balked at having children was a “criminal against the race” and an “object of contemptuous abhorrence.” Women can heave a collective sigh of relief that societal mores about late motherhood have changed, thanks largely to the feminist movement. Still, some gray-haired mothers who find themselves panting after toddlers may still wonder what shape they will be in by the time their kids finally grow up. They may recall hearing that young mothers pass through pregnancy and the postpartum period with their bodies unscathed, while their older counterparts face a higher incidence of varicose veins, high blood pressure, gestational diabetes and other complications. But the assumption that early motherhood is better for your body is not necessarily true, according to a series of recent studies on aging and reproduction. These studies suggest that it behooves women to do what growing numbers of them are doing anyway—have children late and infrequently. Researchers examining twelve centuries of genealogical records have discovered a clear tradeoff between early childbearing and longevity. One recent study showed that women who delay having children until their 30s and 40s, and then have only one or two, are more likely to live into their 80s, 90s and beyond. Female longevity, it appears, is linked to the number of children a woman has and her age at the birth of her first child. Another study showed that centenarians are four times more likely than the general population to have had their first child in their 40s. To any mother who has struggled through sleepless nights or other vagaries of motherhood, the link between number of children and life span seems intuitively obvious. We only have so much energy and each child obviously requires a substantial investment of this scarce commodity. That life span should be correlated to age at first birth seems less intuitive, however. Researchers are careful to point out that older mothers do not necessarily live longer just because they have fewer kids. Indeed, the precise reasons for the importance of age are far from clear. One possible explanation is that if a woman is able to have children relatively late in life, she is clearly one of the genetic elect. The ability to have kids after a certain age may simply be a marker for longevity, as late pregnancy implies late menopause, which in turn implies the delayed onset of age-related disease such as Alzheimer’s, heart disease and stroke. It is also plausible that the timing of first pregnancy resets, or at least interferes with, a woman’s biological clock. Setting a biological timepiece ticking sooner could trigger early menopause while winding it up late in life could delay menopause and rejuvenate middle-aged mothers. Sadly, for men, one of the sacred tenets of evolutionary psychology—that men are naturally more promiscuous in order to propagate the species—may also be a recipe for a shortened life span. Married men with decreased fecundity live longer, and their longevity is in fact correlated to that of their spouse. And those men who invest heavily in reproduction while they are young can expect, on average, shorter lives.