For more than 60 years, evolutionary biologists have debated whether a unique genetic system found in ants, bees and wasps helps explain one of nature's most remarkable innovations: eusociality, a form of social organization in which colonies divide reproductive labor between queens and workers.
A new study from Arizona State University challenges the idea that genetics alone is responsible.
Published in Current Biology , the research shows that while eusociality appears to evolve more frequently in insects with a haplodiploid genetic system, that pattern is almost entirely driven by a single group — the stinging wasps, bees and ants known as the aculeate Hymenoptera. Across insects more broadly, haplodiploidy by itself does not predict the evolution of eusociality.
The findings suggest that the repeated evolution of complex insect societies is more likely explained by traits unique to particular evolutionary lineages, rather than by chromosome inheritance alone.
"People have been discussing this hypothesis for about 60 years," said Sachin Suresh , a PhD student in the School of Life Sciences at Arizona State University and lead author of the study. "There were many theoretical predictions, but formal comparative tests across insects have been surprisingly rare."
Eusociality represents one of the highest levels of social organization found in nature. Eusocial species live in colonies with overlapping generations, cooperate to care for young and divide reproduction so that only one or a few individuals reproduce while the rest function as workers. Ants are universally eusocial, as are honey bees and some wasps, while the behavior has evolved only rarely in other insects such as termites, thrips, aphids and a few beetles.
For decades, one leading explanation has centered on haplodiploidy, a genetic system in which females develop from fertilized eggs and carry two sets of chromosomes, while males develop from unfertilized eggs and carry only one. Because sisters can be more closely related to one another than to their own offspring under this system, evolutionary theory proposed that helping raise siblings could be more advantageous than reproducing independently.
Although the hypothesis has shaped generations of evolutionary research and appears widely in biology textbooks, it had rarely been tested with large-scale empirical data.
To evaluate the idea, Suresh and senior author Timothy Linksvayer compiled social behavior and genetic information for tens of thousands of insect species and mapped those traits onto two of the largest available species-level insect family trees. They then used phylogenetic comparative methods to estimate how often eusociality evolved under different genetic systems.
At first glance, the results seemed to support the long-standing hypothesis: transitions to eusociality occurred more often in haplodiploid insects. But a closer analysis revealed that nearly all of that signal came from a single branch of the insect family tree.
"When we formally tested it, we found there is no real association between the genetic determination system and eusociality," Suresh said. "It has more to do with environmental factors and the life-history traits of insects."
Once the researchers accounted for the exceptional evolutionary history of the aculeate Hymenoptera, haplodiploid insects outside that group showed rates of eusocial evolution comparable to those of diploid insects.
The study also helps reconcile recent research that has questioned the role of haplodiploidy. By analyzing nearly 69,000 insect species across the full breadth of insect diversity, the ASU team demonstrated that apparent links between genetics and eusociality reflect lineage-specific evolutionary history rather than a universal biological rule.
Instead, the findings point researchers toward other factors that may have enabled the repeated evolution of insect societies within ants, bees and wasps. Traits such as stingers, specialized nesting behaviors and other aspects of their biology may have created conditions that favored the evolution of cooperative colonies.
The work provides one of the most comprehensive empirical tests to date of a foundational idea in evolutionary biology and underscores the importance of testing long-standing theories with large comparative datasets.
Current Biology
Data/statistical analysis
Animals
Haplodiploidy alone does not predict the evolution of eusociality
3-Aug-2026
The authors declare no competing interests.