Sex

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Part 2. Humans are (Blank) -ogamous: Promiscuity

This is the second part on the evolution of human mating behavior, comparing evidence for promiscuity and pair-bonding in our species. Please see the Introduction here.

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“I’ll be frank. True monogamy is rare. So rare that it is one of the most deviant behaviors in biology.” (Olivia Judson 2002: 153)

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In their best-selling book, Sex at Dawn, Chris Ryan and Cacilda Jethá suggest that there is a good amount of direct and circumstantial evidence that extended monogamy does not come easily for humans, and that this derives at least in part from our fairly promiscuous evolutionary history. (To clarify, they use the term ‘promiscuous’ not in a judgmental way, but merely to convey having multiple sex partners). Their main premise is that rigid monogamy became common only after our ancestors made the shift from hunting and gathering to agriculture. With agriculture came an emphasis on fixed settlements, private property that could be inherited, genetic paternity, and female sexual fidelity. They argue that this stands in contrast to our hunting-gathering past, when sexual relationships were more open and not confined to an exclusive pair-bond.

Bonobo sex. From Lola ya Bonobo

Bonobo sex. From Lola ya Bonobo

 

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Part 1. Humans are (Blank) -ogamous

“(A)s our forebears adopted life on the dangerous ground, pair-bonding became imperative for females and practical for males. And monogamy – the human habit of forming a pair-bond with one individual at a time – evolved.” (Helen Fisher 2004: 131)

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“Several types of evidence suggest our pre-agricultural (prehistoric) ancestors lived in groups where most mature individuals would have had several ongoing sexual relationships at any given time. Though often casual, these relationships were not random or meaningless. Quite the opposite: they reinforced crucial social ties holding these highly interdependent communities together.” (Chris Ryan & Cacilda Jethá 2010: 9-10)

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 “We are not a classic pair-bonded species. We are not a polygamous, tournament species either…. What we are, officially, … is a tragically confused species.” (Robert Sapolsky)

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The above three quotations were selected to illustrate the range of views that exist on the evolution of human sexual and mating behavior. This is not a trivial matter. To primatologist Bernard Chapais: “The central puzzle of human social evolution… is to explain how promiscuity was replaced by the pair bond” (that is, assuming the pair-bond has gained complete ascendancy). But it’s about more than our ancestors’ mating behaviors. Lurking in the background is the notion that our ancestral behavioral patterns impact current ones, via phylogenetic inertia. Additionally, how we view the past is important because, rightly or wrongly, we have a tendency to associate what is natural with what is good (but note well the naturalistic fallacy). For both of these reasons, the past matters.

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On Fatherhood: Proud Primate Papas

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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?

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