Old men chasing young women: A good thing

It turns out that older men chasing younger women contributes to human longevity and the survival of the species, according to new findings by researchers at Stanford and the University of California-Santa Barbara.

Evolutionary theory says that individuals should die of old age when their reproductive lives are complete, generally by age 55 in humans, according to demographer Cedric Puleston, a doctoral candidate in biological sciences at Stanford. But the fatherhood of a small number of older men is enough to postpone the date with death because natural selection fights life-shortening mutations until the species is finished reproducing.

“Rod Stewart and David Letterman having babies in their 50s and 60s provide no benefit for their personal survival, but the pattern [of reproducing at a later age] has an effect on the population as a whole,” Puleston said. “It’s advantageous to the species if these people stick around. By increasing the survival of men you have a spillover effect on women because men pass their genes to children of both sexes.”

“Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan,” was published Aug. 29 in the online journal Public Library of Science ONE. Shripad Tuljapurkar, the Morrison Professor of Population Studies at Stanford; Puleston; and Michael Gurven, an assistant professor of anthropology at UCSB, co-authored the study in an effort to understand why humans don’t die when female reproduction ends.

Human ability to scale the so-called “wall of death”—surviving beyond the reproductive years—has been a center of scientific controversy for more than 50 years, Puleston said. “The central question is: Why should a species that stops reproducing by some age stick around afterward?” he said. “Evolutionary theory predicts that, over time, harmful mutations that decrease survival will arise in the population and will remain invisible to natural selection after reproduction ends.” However, in hunter-gatherer societies, which likely represent early human demographic conditions and mating patterns, one-third of people live beyond 55 years, past the reproductive lifespan for women. Furthermore, life expectancy in today’s industrialized countries is 75 to 85 years, with mortality increasing gradually, not abruptly, following female menopause.

Grandmother hypothesis

In 1966, William Hamilton, a British evolutionary biologist, worked out the mathematics describing the “wall of death.” Since then, the most popular explanation for why humans don’t die by age 55 has been termed the “grandmother hypothesis,” which suggests that women enhance the survival of their children and grandchildren by living long enough to care for them and “increasing the success of their genes,” Puleston said. However, Hamilton’s work has been difficult to express as a mathematical and genetic argument explaining why people live into old age.

Unlike previous research on human reproduction, this study—for the first time—includes data on males, a tweak that allowed the researchers to begin answering the “wall of death” question by matching it to human mortality patterns. According to Puleston, earlier studies looked only at women, because scientists can reproduce good datasets for humans entirely based on information related to female fertility and survival rates.

“Men’s fertility is contingent on women’s fertility—you have to figure out how they match up. We care about reproduction because that is a currency by which force of selection is counted. If we have not accounted for the entire pattern of reproduction, we may be missing something that’s important to evolution.”

Men and longevity

In the paper, the researchers analyzed “a general two-sex model to show that selection favors survival for as long as men reproduce.” The scientists presented a “range of data showing that males much older than 50 years have substantial realized fertility through matings with younger females, a pattern that was likely typical among early humans.” As a result, Puleston said, older male fertility helps to select against damaging cell mutations in humans who have passed the age of female menopause, consequently eliminating the “wall of death.”

“Our analysis shows that old-age male fertility allows evolution to breach Hamilton’s wall of death and predicts a gradual rise in mortality after the age of female menopause without relying on ‘grandmother’ effects or economic optimality,” the researchers say in the paper.

The scientists compiled longevity and fertility data from two hunter-gatherer groups, the Dobe !Kung of the Kalahari and the Ache of Paraguay, one of the most isolated populations in the world. They also looked at the forager-farmer Yanomamo of Brazil and Venezuela, and the Tsimane, an indigenous group in Bolivia. “They’re living a lifestyle that our ancestors lived and their fertility patterns are probably most consistent with our ancestors,” Puleston said about the four groups. The study also looked at several farming villages in Gambia and, for comparison, a group of modern Canadians.

In the less developed, traditional societies, males were as much as 5-to-15 years older than their female partners. In the United States and Europe, the age spread was about two years. “It’s a universal pattern that in typical marriages men are older than women,” Puleston said. “The age gaps vary by culture, but in every group we looked at men start [being reproductive] later. At the end of reproduction, male fertility rates taper off gradually, as opposed to the fairly sharp decline in female fertility by menopause.”

Despite small differences based on marriage traditions, all women and most men in the six groups stopped having children by their 50s, the researchers found. But some men, particularly high-status males, continued to reproduce into their 70s. The paper noted that the age gap is most pronounced in societies that favor polygyny, where a man takes several wives, and in gerontocracies, where older men monopolize access to reproductive women. The authors also cite genetic and anthropological evidence that early humans were probably polygynous as well.

Older male fertility also exists in societies supporting serial monogamy, because men are more likely to remarry than women. “For these reasons, we argue that realized male fertility was substantial at ages well past female menopause for much of human history and the result is reflected in the mortality patterns of modern populations,” the authors say. “We conclude that deleterious mutations acting after the age of female menopause are selected against … solely as a result of the matings between older males and younger females.”

According to Puleston, the “grandmother hypothesis” may be true, but the real pattern of male fertility extends beyond this explanation. “The key question is: Does the population have a greater growth rate if men are reproducing at a later age? The answer is ‘yes.’ The age of last reproduction gets pushed into the 60s and 70s if you add men to the analysis. Hamilton’s approach was right, but in a species where males and females have different reproductive patterns, you need a two-sex model. You can’t correctly estimate the force of selection if you leave men out of the picture. As a man myself, it’s gratifying to know that men do matter.”

Grants from the U.S. National Institute on Aging supported this study.

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1,793 Responses to “Old men chasing young women: A good thing”

  1. Thank you for this very helpful article. I have found it quite useful.

    March 20, 2012 at 11:31 am Reply
  2. Leslie #

    Guys over 35 have less perfect sperm and so they can produce less healthy offspring. So it would be a disadvantage for a younger woman to be with an older man.

    February 21, 2012 at 1:47 pm Reply
    • ana #

      The title of this site makes me sick. I’m so glad I’ve decided to become a lesbian.

      February 27, 2012 at 5:06 am Reply
      • funki #

        old men are chasing lesbians. Ah Ah Ah Ah Ah! Hee Hee Hee Hee Hee!

        March 6, 2012 at 1:11 am Reply
      • adriandrummond #

        You decided nothing., You were born a lesbian.

        March 14, 2012 at 7:58 am Reply
    • Jon #

      I thought it was only lower sperm count, not the condition of the cells themselves. It’s not las if older men produce mutants you know. I am 41 and would like to have more children, I am in the financial position to provide for them.

      I understand my role in evolution as a protector and provider, and I greatly appreciate womens’ roles as childbearers, mothers, pillars of emotional support for both men and children. I don’t think women should feel like this is demeaning. You should know that being a man isn’t as empowering in someways as you might think. A man’s life can be very demanding, and women in fact have much control over men; more than you probably realize. I have often felt controlled by women and their sexuality, but I am not bitter about it. In the right environment men and women can be mutual benefactors for each other.

      May 13, 2012 at 2:25 am Reply
  3. Novoline Spiele #

    Thx Great Post,I enjoyed the Blog.

    January 25, 2012 at 6:44 am Reply
  4. mj #

    As long as you feel young and enthusiastic,age hardly matters.One should persue his passion with full vigour and courage if u mean it.

    January 17, 2012 at 1:37 am Reply
  5. Drop the royal ‘we’ and get cracking?” What exactly do you mean by that?

    Wouldn’t mind having an explanation that was at least a paragraph long.

    By “we” I meant people in general, not a “royal we”.

    December 22, 2011 at 12:10 am Reply
  6. Custom written term papers #

    Amusing, but lots of interesting text in the post.

    http://www.e-termpapers.com/

    December 15, 2011 at 12:24 am Reply
  7. naughty #

    yes. old men chasing young girls, they are dating..but in reality the young girls are writing the particular and exact “date” to escape with the property and jewels. When the old ones wake up they come to know about the truth, the realisation. They open their eyes really. .She says, “Damn”. ..Want another negative comment, i told you when you were sleeping, now you want another one? Get it, “Close the door”. Old says, “i believed you the chick, …She says, “thats what i wanted”.. am not a green chick.. my huntingcontinues…wait, call for me…yes darling, pass the address..switch off. She says, my bank balance is increasing. :)

    December 13, 2011 at 9:55 pm Reply
  8. Jane #

    It was an interestingly enough article. I don’t judge a book by its covers and have nothing against older men dating younger women, Nor the other way around. Anyway, i found a web site that has interesting information about male breeding and their preferences.
    It’s true that all men like younger women, but not because they breed better, but because they’re beautiful and willing.

    December 9, 2011 at 5:20 am Reply

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