Queen ants, bees, and wasps are so busy giving birth that they don't have time to raise their offspring. To compensate, the queens fill their colonies with daughters who serve as caregivers, like the worker ants pictured above. These designer offspring are a consequence of a reproductive quirk known as haplodiploidy, in which unfertilized eggs develop as males and fertilized eggs become females. Now, zoologists in the United Kingdom suggest that haplodiploidy helped complex societies among insects evolve. The researchers created a mathematical model showing that if daughters are more likely than sons to help raise offspring, insect mothers will produce more daughters. As the daughters fill the colony, it becomes less important for individual females to reproduce, creating an evolutionary incentive for them to raise their siblings. Over time, the mix of rarer males, female helpers, and a queen mother leads to a hierarchical society, the researchers theorize in the current issue of The American Naturalist. The idea has yet to be tested in a lab, but its logic "is beautifully simple and transparent," says Jacobus J. Boomsma, an evolutionary biologist at the University of Copenhagen who was not involved with the study.
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