Human (September 27 post), Mirroring People (September 18 post), and The First Word (August 31 post) all stress the social nature of the human species as something unique to homo sapiens. Marco Iaccoboni, as we saw in Mirroring People, believes that not enough weight is given to our social nature and too much consideration is given to our individuality. But what of other species? We know that other primates are social, although not to the extent of the human species. But there are other species who are even more socially organized than the human species. Meet the social insects --- bees, wasps, ants, termites --- who have established a diverse array of social communities, some of which have suppressed nearly all individuality.
Holldobler and Wilson's The Superorganism does not specifically address the big three areas of human inquiry -- the very large, the very small, and the human mind -- that I described in the August 31st post, but the book is devoted to that other question I mentioned: what is life? The subject-matter of The Superorganism is not entirely divorced from the books in the preceding posts. One of the links between each of the books reviewed in earlier posts is the subject of information and communication. The largest chapter of this beautiful book exhaustively summarizes what we know about communication within the species of the social insects --- not at the level of electrons and quarks and bosons that Seth Lloyd focused on --- but at the level of chemical compounds and the sensory capabilities of these insects: pheromones secreted to lay a trail for colony ants to follow leaders from the nest to food sources and back; odors of hydrocarbons that confirm the queen is present in the colony that shut down the reproductive capabilities of female workers so that only the queen becomes the source of eggs; odors of hydrocarbons that enable ants to distinguish members of their own colony from outsiders. There is also the suggestion, not inconsistent with Christine Keneally's statement in The First Word that human language is believed to have emerged from human motor skills, that insect communication may have emerged from the insect's motor skills.
But information is not the big idea in Superorganism. Information and communication among individual insects and competing groups of insects is just a significant piece of the evidence that supports the big idea in this book: multilevel natural selection. Since Richard Dawkins originally published The Selfish Gene in 1976, a debate has raged whether natural selection operates on genes, as advanced by Dawkins, or whether it operates on the individual organism (phenotype) --- the carrier of a collection of genes, or whether it operates on groups such as related kin, or more broadly communities or colonies. The advocates for each view were said to promote gene selection, individual selection, kin selection, or group selection respectively. Charles Darwin, because he lacked an understanding of Mendellian genetics, DNA and RNA, essentially propounded a view of individual selection, although he acknowledged, as Holldobler and Wilson note, that the altruistic behavior of the insect colony appeared to be an exception. Holldobler and Wilson join an emerging view that declares, "It's all of the above," and hence the nom "multilevel selection." The early advocates for multilevel selection, David Sloan Wilson and and Elliot Sober, refer to it as "a unified theory of natural selection that operates on a nested hierarchy of units." While declaring that "all selection is multilevel," Holldobler and Wilson acknowledge that the ultimate unit of evolution is the gene (or a group of alleles of interacting genes). Even Dawkins concedes, however, that the fate of a gene can be tied to the fate of other genes within the same phenotype, so the lines over the unit of natural selection have blurred as the debate ensues.
The unique case of the social insects posed a question for Darwin because he was bothered by the question of how the worker group of ants and other social insects could evolve if they were sterile and left no offspring. Holldobler and Wilson explain the principle of eusociality --- the care of offspring of a reproductive group by a worker group --- and the gem in this 500 page book is the presentation of a model, supported by some evidence, how the most advanced eusocial insects such as bees and leafcutter ants evolved their cohesive social organization of altruistic individuals over millions of years. While difficult for the lay person such as myself to follow on the first presentation, the theory is advanced by this sentence: "Altruism and eusociality are thus evidently born from the appearance of a phenotypically flexible eusocial allele (or ensemble of such alleles) in a progressive provisioning mother and between-group selection acting on emergent group traits, socially binding in nature and sufficiently powerful to overbalance the dissolutive effects of individual direct (within group) selection." Translation: at the gene selection level, traits are favored to enhance the survival of eggs or larvae by promoting social relationships that become strong enough (ie. that eliminate or minimize conflict within the group) to offset threats from competing social groups (other colonies or species) or the environment. This development was evolutionarily enabled because the alleles within the genes of the individual insects were flexible enough to activate this solution for survival. Finally, "when ecological and genetic factors advance a society to near the upper extreme of the superorganism continuum, subsequent selection may result in the complete loss of costly physiological structures involved in within-group competition" and "the capacity for 'selfishness' [becomes] insignificant because the underlying organs (for example, ovaries) important for within-group competition degenerate or become completely lost." For these unique groups of insects, the authors find that the colony is essentially an organism (phenotype), which they call a "superorganism." Borrowing a term from Dawkins, the authors conclude that the eusocial insect colony effectively becomes a target of natural selection because it is a coherent 'extended phenotype' of genes within colony members.
Importantly, the eusocial insects who form "superorganisms" are a very tiny percentage of the entire landscape of all species. They comprise only 15 species of more than 2600 species of insects. There is one species of vertebrates --- naked mole rats --- who fit this classification. However powerful the evidence for the superorganism is and the multilevel selection model, the truth remains that the critical unit of evolution is the gene. As the fictional character quoted in Richard Powers' Generosity says (see November 30 post), "Genes don't code for traits." Genes do code for chemical stimuli and sensory organs. This is not lost on Holldobler and Wilson who write, "Decision by decision, the insect responds to those stimuli to which its sensory and nervous systems are programmed to respond. These stimuli compose the highly filtered sensory world of the caste to which it belongs." And the science of evolutionary development, which posits that genes may not be expressed until a later developmental stage of life, undoubtedly has a role in explaining how insects "learn" altruistic behavior. Holldobler and Wilson provide evidence for this model as well in explaining that there are some species of female worker ants with ovaries in the nest that are simply suppressed by specific chemical recognition that a fertile egg-laying queen is in the nest, and when the queen dies, a worker ant's reproductive capabilities can be reactivated for the survival of the group.
If the reader of this book is, like me, learning about the social insects for the first time, there is a sense of awe in just how much we know about ants, bees, wasps, and termites. The quantum of information provided by the authors in support of their model, particularly about the ants, can be overwhelming at time. The authors' discussion of genetic social evolution and sociogenesis is delivered early in chapters 2 and 3, and the evidence follows for seven more chapters over 430 pages. After reaching the end of the book, go back and read chapters 2 and 3 again and the enormous amount of detailed evidence will come together.