What are the chances that your dad isn’t your father?

How confident are you that the man you call dad is really your biological father? If you believe some of the most commonly-quoted figures, you could be forgiven for not being very confident at all. But how accurate are those figures?

Questions of paternity are built over the deepest well of human insecurity, for children searching to know who they are, for fathers wanting to know whose kids they are raising and for mothers uncertain about the strength of the bonds holding their families together.

I consulted on an episode of SBS’s Tales of the Unexpected documentary series, “Who’s Your Daddy?” (screening this Sunday April 20) which looks at the issue in some detail.

The program explores the question of paternity certainty, combining three moving tales – each involving a DNA paternity test – with a poll of sexual behaviour in Australia and the US and an exposition of why uncertain paternity presents such a sensitive issue.

One of the three?

How many children are the genetic offspring of someone other than the guy who thinks he is the father?


If you have read, heard or watched anything on this question, you will have encountered many estimates, from 9% to more than 30%. The idea that almost one in three people might be the result of what we biologists rather matter-of-factly call “extra-pair copulations” titillates and horrifies in equal measure.

These estimates surprise most people when they first hear them. So much so that the numbers tend to stick in our minds. But do these numbers bear any truth?

The problem with most data on paternity is the near impossibility of obtaining an unbiased sample. A paternity clinic, for example, is a bad place from which to estimate the rate of misattributed paternity. Many clients are there because at least one party isn’t convinced.

Likewise, any study recruiting families – however randomly – might have more success recruiting mothers who harbour no doubts about their children’s paternity.

Questionable figures

Swinburne University sociologist Michael Gilding, who also appears in the SBS program, has thoroughly researched the origins of the popular belief that 10% to 30% of paternities are misattributed.

He traced the source of the high estimate – 30% – to the transcript of a symposium held in 1972 in which British gynaecologist and obstetrician Dr Elliot Philipp mentioned an estimate from a small sample of parents.

This brief conversation took on a life of its own, despite the fact that Dr Philipp never published the findings of his study. As a result, his precise tests and his population sample were never identified.

Of the many studies that have attempted to estimate the rate of misattributed paternity, the higher estimates have tended to grab headlines, whereas more modest estimates sink without trace.

In whose interest?

Prof Gilding implicates two groups for inflating the public perception of misattributed paternity rates: evolutionary psychologists and fathers’ rights groups.

Evolutionary psychologists, according to Gilding, are so invested in their ideas about the nuanced mating decisions women make that they overestimate how often women mate outside their long-term relationships. My impression is that this may be an accurate assessment of some headline-grabbing research but not universally true of the field.

Fathers’ rights groups represent men negotiating the heartbreak of family break-up. Some such groups also host strident activists propelled by a conviction that the law and society have been utterly corrupted by feminism, gynocentrism and misandry.

The blogs and forums of this netherworld amplify any finding, however flimsy, implying that women are rampantly promiscuous or cynical swindlers looking to part men from their hard-earned cash or dupe them into caring for kids that don’t bear their DNA.

They call this “paternity fraud” and some claim it “worse than rape”.

You won’t find on their websites a critical analysis of the sampling methods or techniques used to estimate paternity misattribution rates, just titanium-reinforced convictions that 25% to 30% of children are being raised or supported by the “wrong” guy.

Why does it matter?

In the ever-dynamic game of sexual relations, the one factor that has always weighed decisively in the favour of womankind is the secure knowledge that she is the mother of her children. According to an old aphorism: “Maternity is a matter of fact, whereas paternity is a matter of opinion.” At least it used to be.

Paternity testing now much easier and cheaper.

Fast-moving developments in molecular biology make paternity testing faster, cheaper and more accurate than ever before. Analysis of foetal DNA in the mother’s blood enable paternity assignment as early as eight weeks into a pregnancy.

Interweaving strands of evolutionary research suggests that paternity confidence forms part of the glue bonding men to their children and to the women who bore them. Undermine that confidence and men invest less readily in the subsistence and safety of their families, and become more likely to abscond.

That is not to say that all men are calculating Darwinian cynics. Many men make magnificent fathers to children that do not bear their DNA. But men get immoderately touchy about paternity. Insecurity over paternity has tectonically shaped much that is least admirable about male behaviour and twisted societies.

But knowledge about paternity can be empowering. It can reassure an uncertain father. It can vindicate an impugned mother or assist her in a paternity suit. And it can help a child understand who they are and where they come from.

What’s the answer?

So how many children are sired by someone other than “Dad”?

Population-wide random-sample DNA testing remains financially and ethically unviable. But to understand some of the behaviours that might lead to paternity misattribution, the SBS documentary producers commissioned Roy Morgan Research to poll samples of Australian and American women.

They asked a number of questions including whether they had conceived a child at a time when they had multiple sexual partners? I was surprised that no more than 2% of women admitted to this.

That suggests a low rate of misattributed paternity; but note the data are presented per woman, not per child. The poll does suggest that mating with multiple men around the time of conception is neither rampant nor pathologically rare.

These results marry comfortably with DNA estimates of misattributed paternity from samples that cross a broad range of societies which suggest the rate is between 1% and 3%, and with Prof Gilding’s estimate of between 0.7% and 2%.

The number of children whose biological father isn’t their social dad is probably far smaller than you’ve been led to believe, although the 30% figure seems to be a zombie-statistic that refuses to die.

But even a 1% rate of misattributed paternity still adds up to millions of individual children, world-wide, each part of an interesting, sometimes tenuous and often heart-breaking story.

The Conversation

Rob Brooks receives funding from the Australian Research Council. He consulted, without remuneration, with the production company (Cordell Jigsaw Zapruder) on the design of the paternity poll and the content of the show, and appears in the program mentioned here.

This article was originally published on The Conversation.
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Have you got the balls to be a good dad?

Dads are important. Pardon the motherhood statement about … fatherhood. Just sometimes, even self-evident things need to be said. All else being equal, fathers who are involved in their children’s upbringing directly improve those children’s survival, health, social and educational development.

Jay-Z rhapsodises about becoming a dad, in Glory (featuring his daughter, Blue Ivy Carter)

Now for the second self-evident proposition: some dads are better than others. A great many dads lavish as much love and care on their children as those kids’ mothers do. And many dads do more. Fathers make all sorts of deep, selfless, sacrifices to meet their children’s needs.

But fathers vary enormously in how involved they are an in the ways they care. According to Anthropologist Sarah Blaffer Hrdy, the contributions that fathers make to child caring and to the family vary dramatically among and within cultures. Far more dramatically, in fact, than the contributions mothers make.

What makes the difference, then, between a superdad and a low-investing or even absentee dad? What distinguishes a guy who raps lovingly about “the child he had with the child from Destiny’s Child” from the papa who was a rolling stone?

The Temptations – sweet moves and even sweeter suits, in a 1972 performance of Papa Was a Rolling Stone

Paternal trade-offs

Tempted as some might be to vilify low-investing men, evolutionary analysis usually seeks first to understand behaviour rather than to judge it. Evolutionary theory certainly can illuminate why fathers don’t all invest equally. And an intriguing study, published today, supports the idea of a biological continuum between high and low-investing fathers.

The key comes from life-history theory, which concerns itself with the economics of how organisms acquire resources and spend them on growth, reproduction, survival and other vital but costly activities. For example, just as one cannot spend the same dollar on rent and food, so one cannot spend the same kilojoule of energy on making sperm and on fighting off an infection. Different adaptive priorities trade-off with one another, just as different spending priorities trade-off within a household budget.

Most men lack the time, money and energy to be both sexually prolific and high-investing fathers at the same time. For some time, life-history theorists have postulated a trade-off between parental investment and mating effort – the investment a man makes in finding, courting and mating with new partners.

No surprises there. Men who spend all their time, money and effort chasing new women are more likely to neglect or even abandon the children they already have. But how does this trade-off arise? Variation in testosterone among men, seems to be right in the middle of this issue:

On top of all this correlative evidence, experimental manipulation in a bird (the Lapland Longspur) reveals that testosterone supplementation directly increases a male’s investment in courtship singing. This comes at the expense, however, of his effort attending the chicks.

Gone Daddy Gone. The Violent Femmes, who, incidentally, take all their equipment on the bus.

Testicle size

The size of a male’s testes also correlates with investment in mating. Species in which females tend only to mate with one male in a given breeding cycle tend to have smaller testes than those in which sperm has to compete with that from other males for the chance to fertilise the same egg. Big testes equals more sperm equals more tickets in the great sperm lottery.

Within species, some evidence suggests that males with larger testes mate with more females and do so more often than less testicularly spectacular males. Large testes take energy to maintain. They also present a vulnerable liability, favouring compactness. Perhaps men whose bodies are biologically geared to invest in courting and mating with new mates might make the risky investment in larger testes, but those aiming for caring monogamy act to minimise their testicular liability?

In a 1995 book, Mark Bellis claimed that testes size was associated with sexual strategies in men. However, Leigh Simmons and colleagues at UWA found no such evidence in a 2004 paper. With this in mind, Jennifer S. Mascaro, Patrick D. Hackett and James K. Rilling from Emory University set out to test the relationship between testicular size, testosterone and men’s parenting effort.

Kurt Cobain’s father issues get a serious airing on Serve the Servants

The Paternal Brain

Mascaro and her collaborators recruited 70 fathers, each with a child aged 1 or 2, and each of whom were living with the child and the child’s mother. The easy part was measuring male testes and plasma testosterone levels. They also administered comprehensive questionnaires to establish which parenting tasks each father performed, from the routine (bathing baby, attend child during the night) to the less common (taking the child to medical appointments).

Anyone who has parented alongside another knows that people don’t always accurately estimate their contribution to the work of caring. So the researchers asked the mens’ partners about who-did-what in the child-care department. Mums and dads actually agreed reasonably well on the division of labour.

And in a welcome development, the team used Functional Magnetic Resonance Imaging (fMRI) to explore brain activity in order to refine the picture of male parental investment. They observed how men responded to pictures of their own child, an unknown child and an unknown adult. And they used a variety of images, capturing a neutral expression, a happy or a sad face for each subject.

High testosterone levels and large testes were each, independently, associated with lower paternal caregiving. The authors interpret this as showing that high T and big testes result in lower paternal engagement. Especially since neither the number of hours men worked nor the amount they earned were correlated with testes size or with testosterone. It’s not as if men switched from one form of investment to another.

I’m no neuroscientist, so I won’t judge the quality of the evidence from that part of the study, but the claims are certainly promising. Fathers with small testes displayed more of the brain activity typically associated with nurturing when viewing pictures of their own child. Especially when the picture showed their child with a happy or sad, rather than neutral, expression. These same fathers were also better dads; at least they were more involved in caring for their infants.

Pearl Jam, in their prime, explore the nuances of paternity in Alive

Dads: born and made

Nowhere in Mascaro’s paper, in this column, or in the surrounding discussion I have seen, has anybody suggested the links are deterministic. Testosterone and testicle volume together only explained 21 percent of the variation in paternal caring. If you’ve got big (but healthy) testicles, that doesn’t make you a bad dad. If you’re low-T you may or may not be a good father, super responsive to your child’s emotional state. So, fathers, I shouldn’t have to say this, but don’t take today’s news personally.

The important point is that we’re starting to come to terms with the complex interplay between biology and social behaviour involved in the all-important business of being a good father.

Collectively, these results provide the most direct support to date that the biology of human males reflects a trade-off between mating and parenting effort.

I wouldn’t disagree with this conclusion. I’m amazed at how neatly the results uphold the prediction and the consistency of four lines of evidence: anatomic, hormonal, neuroscientific and social. This paper gives quite a firm idea of the way in which the trade-off works. And it begins to bridge several traditions of study to build a useful model of how biology and social factors interact to shape behaviour.

But why do men vary so much? I expect an avalanche of interesting research on this question. We do know that human life-histories vary from “fast” to “slow”. Living fast involves early puberty and becoming a parent relatively young. It can be triggered by poverty, inequality, childhood neglect and, interestingly, father absence. Which can create a self-reinforcing cycle. Breaking that cycle involves lots of parental investment, both in nurturing and providing for material needs.

One obvious place in which to begin involves longitudinal studies to explore how the associations form between parental care, testicle size and testosterone. There are some exciting hints that low T men become better fathers, but do better fathers also experience a bigger drop in T? And how do testes wax and wane when men have kids. We don’t really know much at all about whether and how testes size changes over men’s lifetimes.

These many related areas of science remain quite some way off tying the complex mish-mash of factors that shape life-histories to the mating-parenting trade-off. But I believe research in this area has immense capacity to improve the lives of everybody involved.

I’ve enjoyed assembling videos of songs associated with fatherhood. Of course there are many, many more. Please Tweet me @Brooks_Rob with any good suggestions you want to share. Use #DadSongs.

Here are a few extras.

For Saffers of a certain vintage – Just Jinger, Father & Farther

Little Man, by Tom Waits

Father’s Day, by Weddings, Parties, Anything

And talking about testicles:

Down one end of the continuum in almost every respect, we find AC/DC

Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

The Conversation

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In the name of the father: the links between religion and paternity

Religion and sex have had a complicated relationship since the very beginning. Adam & Eve, 1504. Albrecht Dürer

Religious leaders and holy texts share deep preoccupations with sex and reproduction. From Islamic purdah to Jewish menstrual purity laws, to Vatican neuroses about everything from contraception to masturbating nuns, it isn’t difficult to see in all major religions a masculine obsession with reproductive control.


But how did religion and reproduction become so entangled? Perhaps it’s just a hangover from a simpler time, near the genesis of religious beliefs, when sex and reproduction were more straitened. Or maybe societies do better with strong – apparently divine – rules and laws about marriage, fidelity and paternity.

Or perhaps religions arose as a way for the powerful and the anointed to control the reproductive lives of others – particularly for men to control women’s sexual behaviour and reproduction.

We may never get to the bottom of all these questions, but new research suggests religious practices can very effectively assure paternity – the aspect of reproduction that undoubtedly causes men most anxiety (especially in the post-Viagra era). Continue reading In the name of the father: the links between religion and paternity