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Altruism needs selfish genes to evolve after all

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    Altruism needs selfish genes to evolve after all * Updated 16:23 30 May 2008 * NewScientist.com news service * Daniele Fanelli It s a problem that has been
    Message 1 of 1 , May 30, 2008
      Altruism needs selfish genes to evolve after all

      * Updated 16:23 30 May 2008
      * NewScientist.com news service
      * Daniele Fanelli

      It's a problem that has been debated ever since Darwin: how have
      hundreds of species of insects and other animals evolved altruistic
      helpers that give up their own reproduction for the sake of others?

      Recently, the orthodox explanation – that they favour their own genes
      indirectly by helping their kin – has been fiercely challenged by
      Edward O Wilson, one of the most prominent evolutionary biologists of
      our time.

      But now a research team led by William Hughes, of Leeds University,
      UK, claims to have falsified Wilson's predictions, showing that
      genetic relatedness is really the key.

      At the core of the dispute is the theory of kin selection, formalised
      in the 1960s by William Hamilton, accepted by the vast majority of
      modern biologists and defended by Richard Dawkins. According to
      Hamilton's rule, apparent acts of altruism – foregoing reproduction
      to help others, say – are actually self-serving, because they benefit
      the altruist's genes.

      Wilson broke with this view, proposing that altruism evolved because
      it benefits groups, rather than genes. For such "group selection" to
      take place, he argued, animals don't need to be closely related, they
      only need to stick together and cooperate.
      Multiple males

      He argues that this is more likely to occur when individuals tend to
      remain in the nest they are born from. So the high relatedness
      observed in ants, bees and wasps – so-called eusocial species that
      have a queen and sterile workers – is a consequence, not a cause, of
      altruism.

      If Wilson is right, then there should be no correlation between the
      degree of genetic relatedness within insect colonies and the level of
      social cooperation they show.

      To test this, Hughes and colleagues looked at a behaviour that has
      fundamental consequences for colony kin structure – polyandry, which
      occurs when females mate with more than one male. This enhances
      female fitness by producing more variable offspring and is a common
      behaviour throughout the animal kingdom.

      "Birds, reptiles, flies, butterflies, beetles – pretty much all
      species that have been looked at show some level of polyandry," says
      Hughes.
      Ancestral monandry

      Hughes and colleagues looked at the levels of polyandry in 267
      species of eusocial ants, bees and wasps. The last common ancestor of
      these insects was solitary, and eusociality evolved independently on
      eight different occasions. By looking at how the species are related
      to each other over evolutionary time, the team could reconstruct the
      ancestral condition – monandry or polyandry – in each case.

      The team found the ancestral condition was invariably monandry. And
      the same applies to termites, shrimps, ambrosia beetles and most
      other eusocial organisms.

      "[In species excluding ants, bees and wasps] the data is much more
      limited, but it points in the same direction," says Hughes. "You
      always have ancestral monandry when eusociality evolves." In other
      words, close genetic relatedness is crucial to the evolution of
      altruism.

      Eventually, once eusociality is evolved and established, insect
      queens start reaping the benefits of multiple mating, which has
      evolved several times as a secondary condition, says Hughes.
      'Cut and dry'

      Intriguingly, very high levels of polyandry are only observed in
      species where helpers have entirely lost the ability to reproduce,
      becoming permanently sterile castes. Again, this is exactly what kin-
      selection theory predicts, because only when eusociality has become
      irreversible, and workers have no other option but to help, can the
      leash of genetic relatedness loosen.

      Hughes contents that these results would seem to settle the
      longstanding debate revived by Wilson.

      "Wilson predicted that high relatedness evolves after eusociality. We
      show that it is ancestral. It's pretty cut and dry, really," says
      Hughes.

      Wilson, however, does not agree that the debate has been resolved so
      cleanly.

      "Hughes and colleagues did not prove the correlation of eusociality
      and ancestral monogamy, because they have no data on the many lines
      that did not evolve eusociality," he says.

      "And they failed to mention other published explanations of multiple
      insemination in the later stages of eusociality. The weight of
      evidence favors the new explanation of close kinship as a consequence
      of eusociality, as laid out in my BioScience article."

      Hughes accepts that there is much more to altruism than simple
      genetic benefits.

      "It is good to be challenged about our hypotheses," says Hughes,
      "Hamiton's equations have three components in them but we have become
      very focused on relatedness. [Wilson] has done us a service in
      drawing attention back to ecological benefits and other components."

      Journal reference: Science (DOI: 10.1126/science.1156108)
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