March 12, 2011

Human natural societies flexible and not primarily built on genetic kinship

Understanding hunter-gatherer societies is important because we are after all just paleolithic peoples dumped into Market Street. Our flexibility allows us to deal with this strange unnatural reality with some ease but this is not the context in which we evolved, not at all.

New research in this ancestral reality of us, embodied in a variety of surviving hunter-gatherer groups, provides some interesting results:


Abstract

Contemporary humans exhibit spectacular biological success derived from cumulative culture and cooperation. The origins of these traits may be related to our ancestral group structure. Because humans lived as foragers for 95% of our species’ history, we analyzed co-residence patterns among 32 present-day foraging societies (total n = 5067 individuals, mean experienced band size = 28.2 adults). We found that hunter-gatherers display a unique social structure where (i) either sex may disperse or remain in their natal group, (ii) adult brothers and sisters often co-reside, and (iii) most individuals in residential groups are genetically unrelated. These patterns produce large interaction networks of unrelated adults and suggest that inclusive fitness cannot explain extensive cooperation in hunter-gatherer bands. However, large social networks may help to explain why humans evolved capacities for social learning that resulted in cumulative culture. 

A news article is also available at Science Daily.

What may seem a bit unexpected is how this social structure is not at all like any related primate group. Our closest relatives live in individual units (orangutans), in single-male dominated harems (gorillas), in patrilocal promiscuous communities (chimpanzees) and in matrilocal even more promiscuous ones (bonobos). 

Instead humans form bands, typically of some 28 individuals, which are neither patrilocal nor matrilocal, and end up including people who are mostly not even closely related to each other. There it goes genetic egoism down the toilet!

This structure actually seems to integrate wider networks of relationships beyond the band, which (from other sources) is typically so flexible that it loses and gains members very frequently. Probably what this implies is ethnic (tribal) networks as main unit, however not even these are closed to strangers, not at all.

The research included some 5000 people from the following nations: Gunwinggu (Australia), Labrador Inuit, Apache, Ache (America), Mbuti, Aka (Africa), Agta and Vedda (Asia).


Update (Mar 17): Blackbird, who runs some interesting blogs on non-human animals you may want to check, mentions that our Pan sp. cousins, both chimpanzees and bonobos, may not be as gender biased as we used to think in regards on who moves and who lives in the established community. The following paper addresses this matter a bit and also includes an interesting analysis of haploid genetics among bonobos (all of which live in D.R. Congo):

Jonas Erikson et al, Y-chromosome analysis confirms highly sex-biased dispersal and suggests a low male effective population size in bonobos (Pan paniscus). Molecular Ecology 2006. [doi: 10.1111/j.1365-294X.2006.02845.x]

He (Blackbird) suggests, and he may be right I'd say, that this ambiguity of locality is similar to what Hills observes for Homo sapiens and may therefore be a shared pattern among the super-genus.  

4 comments:

  1. A cool study! I am glad you covered it. I also liked Chapais News and Views, in which he draws attention to two consequences of predominant monogamy: recognition of patrilineal lines (kids know who their dad is, dad knows who his kids are) and also the inclusion of the "in laws" in your relation system. You care about your in laws because they have the same interest in your kin be your own kids (your parents in law) or your nephews/nieces (your sisters/brothers in law. I don't think kin selection disappears, but instead, that kin selection can work in different ways.

    ReplyDelete
  2. I think it works in a much looser. After all, when you work for people in your wider community it is also for people in your wider kinship circle and most of your genes are in them anyhow (and they are going to work for other people who also have most of your own genes).

    After all maybe you are 50% your dad and 50% your mum, but your dad and your mum also share a lot of that 50%, even if they are not apparently related, just because they are both humans and because they are (typically) of the same community, which share ancestors at many layers in a chaotic way.

    The difference between working for your closes kind and working for a random other human is not that big, anyhow. In both cases you are investing in your own genetic future, maybe marginally more in the first case but not radically more.

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  3. I forgot, bonobos, line chimps, are also predominantly patrilocal, see
    http://www.eva.mpg.de/primat/pdf/ErikssonbonoboY2006.pdf

    But, I quote from the same paper:
    "But female migration is not ubiquitous in chimpanzees, as females also sometimes remain and
    reproduce in their natal group (Goodall 1986; Boesch &
    Boesch-Achermann 2000)."
    so there might be in both chimpanzees and bonobos that the origins of human pattern - more balanced pattern of patrilocality and matrilocality are found.

    ReplyDelete
  4. Very interesting paper, Blackbird. It really suggests that there is more ambiguity in the migration patterns of genders within our Pan sp. cousins (both species), much as is suggested by Hill for humans.

    Very much worth a mention. Thanks.

    ReplyDelete

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