New Study Challenges Long-held Beliefs on Insect Eusociality

Research from Arizona State University suggests that the complex social structure known as eusociality in insects, traditionally linked to haplodiploid genetics, may be influenced more by biological traits than by genetic inheritance alone. This finding, published in Current Biology, has emerged from over six decades of debate among evolutionary biologists regarding the factors that drive eusociality.

Eusociality, seen as one of the most advanced forms of social organization, includes species such as ants, honey bees, and some wasps that form cooperative colonies with overlapping generations and shared reproductive responsibilities. However, the phenomenon has rarely appeared in other insect groups.

For many years, researchers believed haplodiploidy—a genetic system wherein females are diploid, developing from fertilized eggs, and males are haploid, developing from unfertilized eggs—was a key factor in the evolutionary success of eusociality among ants, bees, and wasps. This system allows sisters to be more closely related to each other than to their own offspring, leading to theories that females might gain greater evolutionary advantages by assisting their sisters rather than reproducing independently.

Sachin Suresh, a PhD student in the School of Life Sciences at ASU and lead author of the study, noted, “People have been discussing this hypothesis for about 60 years. There were many theoretical predictions, but formal comparative tests across insects have been surprisingly rare.”

Reassessing the Role of Genetics

Suresh and senior author Timothy Linksvayer conducted a large-scale analysis of social behavior and genetics across tens of thousands of insect species. Utilizing phylogenetic comparative methods, they explored the frequency of eusociality evolution relative to different genetic systems. Initial results seemed to support the connection between haplodiploidy and increased eusociality. However, deeper investigation revealed that this association was predominantly driven by the aculeate Hymenoptera, which encompasses stinging wasps, bees, and ants.

After accounting for the evolutionary history of this group, the researchers discovered that haplodiploid insects outside of Hymenoptera exhibited eusociality at rates comparable to those of diploid insects. “When we formally tested it, we found there is no real association between the genetic determination system and eusociality,” Suresh stated. “It has more to do with environmental factors and the life-history traits of insects.”

Insights from 69,000 Insect Species

By examining nearly 69,000 insect species, the study indicates that the previously assumed link between haplodiploidy and eusociality is largely an artifact of lineage-specific evolutionary history, rather than a universal biological principle. This new perspective shifts focus toward other factors—such as stingers, specialized nesting behaviors, and additional biological characteristics—that may have facilitated the repeated evolution of eusociality in certain insect groups.

The research delivers one of the most comprehensive empirical tests of a foundational theory in evolutionary biology, emphasizing the importance of large comparative datasets in re-evaluating long-standing scientific ideas.