Insect Societies, Superorganisms and the Ratchet of Life's Complexity
In our century of data-driven biology it is not always appreciated that biology has an encompassing theory of adaptation. In terms of what Darwin actually explained rather than conjectured, "The Origin of Adaptation" would have been a better title of his seminal book than "The Origin of Species". However, the theory of adaptation could not be completed until the key mechanism of inheritance became integrated in evolutionary theory during the early 20th century. The insight that genetics is particulate (binary) rather than some unspecified blending process spurred all modern developments in molecular biology. It also led to a new 'gene's eye' view of adaptation, which focuses on how genes maximize their representation in future generations by inducing small cumulative changes that promote their success in competition with alternative variants at the same chromosomal loci.
William D. Hamilton and George C. Williams independently established the 'gene's eye' view of adaptation in the 1960s. Hamilton's version, known as inclusive fitness or kin selection theory, became most influential because it explained reproductive altruism as a consequence of the expression of selfish genes (a metaphor coined by Richard Dawkins). The logic is summarized in Hamilton's rule, a simple inequality saying that any gene inducing reproductive altruism (helping someone else to reproduce) would spread if brs > cro. Here, cro is the gene-level opportunity-cost of not having offspring to which one is related by ro, and brs is the benefit in gene copies passed on to future generations via the offspring of siblings (or lesser kin) to which one is related by rs. Inclusive fitness theory makes many testable predictions of what social traits should have (or not have) evolved, which have been confirmed by empirical research with very high consistency.
Social insects have been prominent test beds for inclusive fitness theory because their workers remain often or always unmated, which leads to forms of sterility that only make sense if relatives benefit. Workers of insect societies are only conditionally unmated, but permanent unmatedness (Darwin's neuters) can make massive superorganismal colonies evolve. After introducing some general natural history, I will highlight the awesome social adaptations of fungus-farming leafcutter ants. I will then show that their superorganismal colonies are also frightening anomalies, because all individual agency ('freedom') that we normally associate with societies has been lost. Finally, I will discuss the most likely causal mechanisms that have induced evolutionary transitions from society to superorganism, including the close analogies with reproductive altruism among cells that gave rise to multicellular organisms.