The economics of hunter-gatherers...

Today, a presentation by Dr. Kim Hill, a rather prolific contributor to the evolutionary behavioral ecology end of anthropology, covered some basic concepts behind the resource sharing in hunter-gatherer tribes.  The crib notes of which can be summed as such:

1. Within most bands, food sharing is both universal and something people make an effort at by producing more than they need, even when the food mass is easily controllable (like fruit collection).
2. Food sharing both covers day-to-day variation in hunting returns and loss of hunting returns during disability/injury.
3. The net resources generated (calories obtained - calories consumed) are positive for adult single males, grandparents, and young married pairs very early in their reproductive history.  During the most reproductive period (30-54), most families have a net loss of resources.
4. Most hunter-gatherer families are cooperative breeders, supplementing their resource needs indirectly through food sharing within the band and by utilizing family "helpers" within the family in the form of:
1. Temporarily single men/women.  (Either pre-marriage adults, between marriage adults, or grandparents) OR
2. Non-reproductive males.

One of my classmates, a graduate student wondered why single men would support other people, considering they typically are the source of greatest surplus resources.  Dr. Hill suggested kin selection could be at work--the kids of their siblings have their genes--the potential that effort is advertising for marriage partners, and that some males simply aren't that attractive to mates.  The discussion also went toward a possible utility--in conjunction with kin selection--for male homosexuality as well the fact single males on their own have no safety net.  A single injury or run of bad luck and they would starve to death.

My suggestion--only partially tongue in cheek--was adultery and "shadow polyandry".  Essentially, cheater males trade on both kin selection and the chance at fathering children surreptitiously.  This way, their contribution has indirect fitness returns as well as the potential for direct fitness returns.

For example, consider the single male--interested in survival--has the following options:

• Be a husband.  The benefit--primarily--is "unrestricted access" to a woman and some degree of acknowledged paternity.  In the short term, this probably ramps up his paternity certainty a bit, depending on the wife's willingness to cheat.  Long-term, this means a better chance at having adult children to provide for him if he's old or disabled as well as more direct fitness.  The cost is primary responsibility for providing for his family. 
• Be a helper.  The primary benefit of being a helper is indirect fitness at about 50% of the value to his sibling(s)*.  Additional benefit can be accessed if being a helper offers an advantage later like mate access or additional help after mating.  The cost is primarily opportunity cost for having his own family, but that depends on mate availability.
• Be a cheating helper.  This hybrid strategy would entail the baseline (indirect) benefits for the helper strategy, but add the chance adding some direct fitness benefit through cuckolding another man.  The cost would depend on getting caught and social consequences (if any).  The incentive to employ this strategy would be (temporary) access to a mate he might not otherwise gain permanent access to.

However, it does take two to tango, so to speak.  What would be in it for the woman? 

The greatest advantage might be accessing continued needed assistance, either directly--if she chose, say, her brother-in-law--or indirectly through keeping and maintaining rapport with other single males.  Additionally, she could use it to access healthy genes from a male that's unable/unwilling to be a husband.  Finally, if she gets pregnant from such a liaison, she creates more variability in her offspring's genes which can translate into better immune function or increased variation in ability or attractiveness.

This is predicated on the fact her fertility risk isn't obvious at the time.  Otherwise, it removes part of the incentive for males to cheat.  Of course, this is true for humans and unlike the chimpanzee.  By having concealed ovulation, women have the opportunity to ply such a strategy and compel males to adapt to it, creating flexibility in the system and bringing more female choice into the reproduction equation...

...which is probably why one of the more interesting differences between chimpanzees and humans is the evolution of more information in the human Y-chromosome.  In this model, it pays to be slightly different for males.

Of course, how to test the idea...

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* - Fitness is estimated as the percentage of one's genes in the next generation.  For a parent, this relatedness is .5 because only half of the parent's genes are passed.  Between siblings, the assumption is also that they share about .5 relatedness because of random assortment of chromosomes.  These are multiplicative, so a sibling's children would have a relatedness of .25 (.5 x .5).