E Pluribus Unum: GBE Virtual Collection on the Evolution of Sociality

Evolution is sometimes construed as a “selfish” process, as selection favors individual reproductive success. However, benefiting your kin can also enhance evolutionary fitness by promoting the survival and reproduction of genetically related individuals. Sociality—broadly defined by Rubenstein and Abbot (2017) as the occurrence of cooperative group living—has evolved repeatedly across the tree of life; yet, how can the complex behavioral and life-history changes required for cooperative living arise from information encoded in a genome?

Insects are ideal models to study the evolution of sociality. From subsocial earwigs or beetles in which parents provide care to their offspring, to the complex eusocial colonies of bees, ants, and termites with reproductive division of labor and cooperative brood care, the diversity of social strategies in insects is remarkable. But how does such a complex suite of traits evolve? In a new Review article in Genome Biology and Evolution, Barkdull and Moreau (2026) review the genomic causes and consequences of sociality in insects; to further draw attention to this key topic in evolutionary biology, GBE releases its newest virtual collection on the “Evolution of Sociality” where we highlight some of our most recent research on this topic across species.

Historically, this field has focused heavily on the evolution of eusocial hymenopterans (bees, wasps, ants, and kin; Fig. 1). In these species, females develop from fertilized diploid eggs, while males do so from unfertilized haploid eggs. This observation has led earlier studies to hypothesize that this system of sex determination, known as haplodiploidy, could be a necessary genomic pathway toward eusociality. After all, the higher relatedness among sisters in haplodiploid species (when compared to diploids) should promote kin selection. Megan Barkdull (Fig. 2)—Assistant Curator of Entomology at the Natural History Museum of Los Angeles County and first author of the new GBE Review—explains that new statistical approaches focusing on the phylogenetic distribution of haplodiploidy and eusociality show this is not necessarily the case. “Eusociality can, and has evolved, in non-haplodiploid lineages like termites and some ambrosia beetles; at the same time, many origins of eusociality are found in the Hymenoptera, a clade with just a single origin of haplodiploidy,” Barkdull elucidates.

Fig. 1.

Harvester ant workers (Pogonomyrmex sp.) entering and leaving their nest. Credit: Megan Barkdull.

Fig. 2.

GBE Author Spotlight: Megan Barkdull. Dr. Megan Barkdull is an assistant curator in the Entomology Department at the Natural History Museum of Los Angeles County. Her research combines genomics, fieldwork, and museum collections to better understand the evolutionary and developmental basis of complex traits in insects, with a particular focus on worker plasticity in ants. She is also passionate about using collections-based outreach and community science to broaden participation in biodiversity research.

Much less is known about the genes and molecular pathways that are associated with the rise of sociality. Barkdull and Moreau (2026) review genomic and gene expression studies showing how selection on genes linked to multiple biological functions, including growth or sensory and cognitive capacity, may facilitate the evolution of sociality. Isolating these genomic signatures can, however, be particularly challenging due to the deep evolutionary history of this phenotype in many social taxa. For Barkdull, however, the large diversity in strategies found among social insects may help to overcome some of these limitations: “Comparing very closely related solitary and social groups is an approach which mitigates the risk of important evolutionary processes being obscured by millions of years of evolutionary divergence,” she says, adding that “Socially polymorphic and facultatively social lineages are excellent study systems for this kind of approach.”

In evidence of the depth and breadth of this field, we have pulled together a virtual collection to exemplify how researchers are leveraging the diversity in social strategies among insects. Ploessl and Jones (2026) investigated the evolution of transcription factor motifs in 42 bee species that differed in social strategy, finding that motif expansion following the gain of sociality was more frequent than motif loss following evolutionary reversion to solitary strategies. Favreau et al. (2023) analyzed brain gene expression data of six species of bees and wasps with rudimentary social organization systems, uncovering a core set of genes consistently associated with social phenotypes in these species. In another facultatively social hymenopteran, the small carpenter bee, Huisken and Rehan (2023) found that gene expression patterns associated with foraging behavior can change depending on each individual's reproductive role and social environment within a group.

Such findings illustrate how differences in social behavior can be associated with changes in gene expression. More broadly, environmentally responsive changes in gene expression may contribute to phenotypic plasticity by allowing individuals with the same genome to develop different phenotypes depending on their social context. In eusocial insects, this plasticity may underlie the development of distinct castes with highly divergent phenotypes and reproductive roles. “When attempting to understand how genomes have evolved to generate sociality, it is critical that researchers ask questions about the evolution of non-coding gene regulatory sequences, moving beyond the focus on protein-coding genes that has historically predominated in the field,” says Barkdull, emphasizing the role of gene regulation.

Sociality is a byproduct of the genome's expression, but Barkdull and Moreau (2026) contend that sociality as a life-history trait also drives genome evolution. “Sociality results in profound changes to how populations are organized, including a reduction in the proportion of individuals who are capable of reproduction and a shift toward longer-lived reproductive lives,” Barkdull mentions, then pointing out that “the most important consequence of these social traits is likely a reduction in effective population sizes, which results in stronger genetic drift and weaker selection.” In a 2023 article in GBE, Barkdull and Moreau themselves analyzed 22 ant genomes to find footprints of changes in mode of selection associated with shifts in reproductive division of labor and worker polymorphism (Barkdull and Moreau 2023).

Looking forward, opportunities abound to explore the evolution of sociality, in insects and beyond. As alluded to in another GBE Review earlier this year by Brenman-Suttner and Zayed (2026), ongoing advances in phylogenetics and gene expression approaches have opened the door for a better understanding of key social traits such as behavioral plasticity or caste differentiation. These methodological advances must be paired with conceptual changes in how researchers approach the field: “It will be key to ask questions that disaggregate the individual component traits that make up sociality, including aggregation, sibling care, or reproductive skew,” says Barkdull.