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For Father’s Day, Scientific American compiled a series on the biology of fatherhood, including a list of 8 species where males are integral in raising offspring. Included were birds (rheas, emperor penguins), mammals (marmosets, red foxes, wolverines), fish (catfish, sea horses), and even insects (giant water bugs). For some of these species, male parental investment extends to carrying fertilized eggs until they hatch. In others, it entails postnatal protection and/or procurement of food for young offspring.

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Two things stand out. First, although the list didn’t claim to be comprehensive, at just 8 examples, it seemed quite short (they couldn’t make it to ten?). In addition, there’s just something peculiar about highlighting species that exhibit good fathering skills to begin with. Consider how odd it would be to encounter a list of species where mothers care for offspring. In mammals, it seems almost tautological that parenting is associated with motherhood since they alone can gestate and lactate. However, there may be rare exceptions to this, such as lactation in male fruit bats (Kunz and Hosken, 2009), and possibly in Robert De Niro, though this issue remains unresolved. Are species with active fathers the exception to the rule? What good are males, then?

For sexually reproducing species, the minimum contribution of males to offspring is their genetic material, delivered via sperm. In fact, in some animals, males are not even essential in reproduction, and females are capable of parthenogenesis (that is, ‘virgin births’). For a female to bear young that contain only half of her genes, there must be some benefit. The accepted wisdom in biology is that sex likely evolved as a means of generating variation in offspring.

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In asexually reproducing species, variation is acquired through mutations and horizontal gene transfer (Jain et al, 1999), but for the most part offspring are clones of their progenitors. Rather than have offspring that are essentially parental copies, adapted and pigeon-holed into some ultra-specific niche, sexual reproduction serves to hedge one’s bets against unpredictable challenges in the environment, such as potential ecological change. The constant creation of varied offspring seems especially necessary in the fight against infectious disease in order to fight rapidly evolving micro-invaders (aka the ‘Red Queen Hypothesis;’ van Valen, 1973). As Matt Ridley put it, parasites invent new keys; hosts change their locks. By shuffling genes around, two parents can create an array of genetic combinations in their children. If you have siblings, think about how different you look from them. Or, look at the photo below of these two beautiful fraternal twins. Same parents, many possible reproductive outcomes.

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Beyond this, fathers (sometimes) contribute more than genes to their offspring. After all, the name of the game in evolution is not merely to have offspring, but to have offspring who make it to the age of reproduction, who are then capable of having their own offspring. Surely, active parenting increases those odds. Two parents increases them further. However, active fatherhood in mammals seems to be rare. In Sarah Blaffer Hrdy’s words:

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“In the majority of (the 5,400 or so species of mammals), fathers do remarkably little beyond stake out territories, compete with other males, and mate with females… By comparison, males in the order Primates stand out as paragons of nurturing, unusual for how much protection and even direct care of young they provide” (2009: 159).

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Hrdy delineates fathering as direct or indirect (where males are not ‘hands-on,’ but remain nearby to protect offspring from rival males), and obligatory (infants don’t survive without it) or not. Direct paternal care seems to be present in about 40% of primate species, particularly in baboons, titi monkeys, and marmosets. It helps that primate infants, like most mammals, are perceived by parents as ‘cute,’ inducing a nurturing response. Imagine if infants were born large and fully formed, like an adult Will Ferrell, and you can see how that would stifle the desire to care for them. Size constraints necessitate that infants must be tiny, but cuteness and helplessness are signals for attention.

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However, direct care seems to be virtually absent in the great apes, which seems odd since they are our closest relatives, and infant development in apes is slow. Male apes may remain near their offspring, but according to Hrdy they do not hold them or go out of their way to provide them with food. The bombshell that Hrdy drops is that fathering does not exactly come naturally to humans either despite the fact that human infants require the most care of any species on the planet. Some men are fathers; some are dads:

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At the end of the day, we are still left with a perplexing paradox: If men’s investment in children is so important, why hasn’t natural selection produced fathers as single-minded and devoted to child-care as titi monkeys, California mice, or dwarf hamsters?” (p. 162)

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Hrdy (by the way, I recommend her book, if it isn’t obvious) points out how incredibly varied and flexible fathering is in humans. She notes that even in some hunter-gatherer populations the amount of paternal investment in childcare is at least partially dependent on circumstances, including the availability of others, such as the mother’s kin, to act as “alloparents.”

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What we’re left with is a nuanced view of fathering in humans. The bottom line is that human infants and children are highly altricial, and they won’t get very far without parental care. But Hrdy argues that we have an outmoded view of the father’s role in the ‘nuclear family’ as a product of natural selection. Fathers are only part of the equation in raising offspring, and human behavioral flexibility means that parental care can come from many places, including grandparents, older siblings, aunts and uncles, or non-biologically related adoptive parents. To end with one more quote from Hrdy:

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Of course, it takes more than one person to rear a child. However, the studies have not been designed to determine whether that second person needs to be male and a genetic parent… Are there multiple caretaker arrangements that are almost as good, just as good, or even better than two parents? We don’t know, because we are rarely asked” (p. 145).

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Related Posts

On Parenthood (June 7, 2011)

The Power of Love (Apr 3, 2010)

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References

Hrdy SB. 2009. Mothers and Others: The Evolutionary Origins of Mutual Understanding. Belknap. (Link)

Jain R, Rivera MC, Lake JA.1999. Horizontal gene transfer among genomes: The complexity hypothesis. Proc Natl Acad Sci U S A. 96(7): 3801–6. (Link)

Kunz TH, Hosken DJ. 2009. Male lactation: why, why not and is it care? Trends in Ecology & Evolution 24 (2): 80- 5 (Link)

Van Valen L. 1973. A New Evolutionary Law. Evolutionary Theory 1: 1-30.

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