Only by conceiving of evolution as acting upon entire populations rather than individual organisms can we understand eusociality -- the mysterious, seemingly "altruistic" behaviors exhibited by insects who forego reproduction in order to care for a colony's young.
So says Edward O. Wilson, the legendary sociobiologist, environmentalist and entomologist, in an article published in the January issue of Bioscience. Wilson doesn't extrapolate from bugs to people, but his conclusions raise fascinating questions about the evolutionary aspects of non-reproducing humans.
Observed in some species of ants, bees and wasps, eusociality has perplexed researchers unable to explain -- in traditionally evolutionary terms, at least -- how entire insect castes could have evolved not merely to refrain from reproducing, but to care for genetically distant larva.
Wilson discussed eusociality in his 1975 book Sociobiology: The New Synthesis, which jumpstarted the field of modern sociobiology by connecting complex behaviors to evolutionary trends. He explained the phenomenon as one of kin selection: evolution didn't act on individuals, but groups of closely related individuals.
However, says Wilson, new findings make kin selection an incomplete explanation. He points to the emergence of eusociality in insect species that don't possess haplodiploidy, a mechanism of sex selection that makes females more genetically similar to their sisters than their offspring. If kin selection drove eusociality, then it should have emerged primarily in these species. Moreover, most haplodiploid species are not eusocial.
Wilson thinks eusociality evolved as a group-level adaptation for out-competing other insect colonies for food: with some colony members devoted to protecting eggs and larva, others could forage farther abroad. All that's needed to take this evolutionary step is the rise of a gene -- or system of genes -- that makes workers want to stay home and help rather than leave the colony and reproduce elsewhere.
The theory is far from settled. No such allele has been identified, and theoretical biologists haven't been able to model it. Bert Hoelldobler, an Arizona State University entomologist and co-author with Wilson of a recent book on ants, said in an email that his friend "is mistaken when he uses low degree of relatedness in highly advanced eusocial systems as evidence for the insignificance of relatedness for the evolution of eusociality."
All this debate might seem like an academic diversion, but for the incredible success of eusocial species. "While only 2% of known insect species are eusocial," writes Wilson, "these species comprise most of the insect biomass." While one has to be careful in drawing early conclusions and then applying them to people, it's clear that in some ways this cooperative system, so much more subtle than the classically self-centered Darwinian ideal, is extraordinarily successful.
So with all necessary caveats against reductionism and misappropriation, we can ask: should human societies conceive of themselves in terms of group-level selection? Have we already developed aspects of eusociality? And -- just to make matters really interesting -- could non-reproducing humans, such as (most) gays and lesbians, as well as heterosexuals who choose not to have kids, actually be a manifestation of this emergent eusociality?
Citing eusociality in defense of any lifestyle choice, even theoretically, could backfire: it implies a subservience of individual well-being to the greater good. But at least it suggests that certain unorthodox lifestyles might not be so "unnatural" after all.
Insects' 'giant leap' reconstructed by founder of sociobiology [press release]
One Giant Leap: How Insects Achieved Altruism and Colonial Life [BioScience, subscription required]
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