Remember the tv show Hercules
that presented tales of the adventures of Hercules and Iolaus? Well, they had more interesting adventures than even that good series was capable of showing. According to Plutarch, the fidelity of Iolaus to Hercules (but not vice versa) was so famed that male couples would use him as an example and profess their fidelity to each other at the tomb of Iolaus.
"And as to the loves of Hercules, it is difficult to record them because of their number; but those who think that Iolaus was one of them do to this day worship and honor him, and make their loved ones swear fidelity at his tomb."
- Plutarch, "Eroticus", par. 17
"It is a tradition likewise that Iolaus, who assisted Hercules in his labors and fought at his side, was beloved of him; and Aristotle observes that even in his time lovers plighted their faith at Iolaus' tomb."
- Plutarch, "Life of Pelopidas", Clough translation
Sexual fidelity, however, is such a rare thing. Not just among humans but also other animals. Rare, though, is not the same thing as absent. According to a PubMed
"The Wandering Albatross provides a striking exception to partner infidelity. This albatross is one of the most remarkable animals in the world (Figure 13). These enormous birds, with a wingspan that measures 11 feet, the longest of any bird (one wing is as long as your outstretched arms), mate for life, which is often 6 decades or longer."
I had originally thought that maybe "til death do us part" would have made a lot more sense for humans back when we only lived to our 30s, but this albatross proves that it is natural (for them) even across long lifetimes. A few days ago, news broke about a study that found what seems to be an infidelity gene
that was linked statistically to the strength of the bond that a male (human) feels to his partner. Men without the gene had higher fidelity and higher relationship satisfaction (as reported by their partner). Men with one copy of the gene had lower scores on those attributes. Men with two copies of the gene had even lower scores. The researchers looked at this gene after it was previously found to play a role in the fidelity of male voles (a small rodent).
When talking about the feature in humans, it's much too easy to get caught up in political maneuvering instead of rational inquiry. Since that article, though, I've been pondering what sexual reproductive strategy would be "best" for a species (any species) given a few starting conditions:
- males and females have comparable abilities (no significant disparity in survival skills individually)
- long lifespan (>60 years)
- long child development (>15 years)
- one adult is designated primary caregiver for each child born
- permanent sexual fertility (not annual/seasonal like many animals) across lifespan
- pathogens that can kill "quickly" (<2 years)
Given those simplistic terms, what reproductive strategy yields the highest number of healthy children?
I find that #3 takes precedence. Since child rearing takes so very long, it requires more resources than can reasonably be expected from only one adult. (Let's call that Corollary 3a.) I see some kind of fidelity involved in arranging for these long relationships. Why? If sexual attraction is responsible for creating children, then anyone who creates a child will want to ensure that another adult can be relied upon to continue providing resources. If sexual attraction produced one child, then it can produce another with a different sexual partner, leading to loss of resources to the first child's primary caregiver.
At first, I kept thinking that some form of group fidelity would be an excellent arrangement. If the group remains small, then problems introduced by #6 can still be minimized. Even if one particular partner dies, then the cost of child rearing can still be shared amongst the other available (and committed) adults. Sounds great. But then I realized the complication that appears across generations. The group must continually bring in new members to avoid inbreeding. In return, it must continuously shed old members to other groups. So the pathogen issue comes up again. Unless (cruelty alert) newcomers are quarantined for the 2 years during which pathogens can make their presence apparent.
So I was back to shrinking the group down to only a couple. Pathogen involvement is limited (with fidelity). Except, of course, when one partner dies and the remaining partner looks for a new caregiver to share in child rearing. But at least risk affects only one adult and their children rather than an entire group.
Promiscuity is excellent at avoiding the inbreeding problem (thereby introducing necessary genetic variety) but loses its luster when faced with the pathogen problem. The only way I can get it to "work" is if transmission of genetic material (mating) happens only once and then the receiving partner maintains the genetic material to use slowly across time. Some animals can do that for short periods of time. In this scenario, pathogen exposure (sexually transmitted, anyway) happens only once. If the receiving partner survives, then they can continuously produce offspring from that one encounter. No additional risk necessary. Then finding someone to share resources during child development would likely occur in groups only with other surviving child-producers (since they have proven themselves free of deadly pathogen). It could be the females (like mammals) or the males (like the seahorse), whichever protects the fetus during development.
So that's the best that I can come up with, examining things without involving religious tradition or political propaganda. My 6 starting rules seem to yield 3 possible outcomes that are very good for the stated goal of producing lots of healthy children.
- binary couples with fidelity
- group structure with fidelity and newcomer sequestration
- random promiscuity during sole lifetime encounter, followed by parent-group association
Did I miss something?