Stick Insects Figured Out How to Ditch Males. It Took Only 8,000 Years

About 8,000 years ago, two species of Mediterranean stick insect hybridized, and something unusual happened to the offspring: they found a way to keep reproducing without ever fully committing to sex again. What followed was one of the stranger documented journeys in evolutionary biology.

Researchers studying the stick insect genus Bacillus traced the reproductive histories of more than 500 wild-caught individuals from Sicily, mainland Italy and France, and found that all hybrid lineages share a single origin roughly 8,000 years ago.

The first stop after hybridization wasn't parthenogenesis outright. It was something called hybridogenesis, a mode of reproduction in which one parent's chromosomes are transmitted clonally while the other set is eliminated and reintroduced each generation through mating. Think of it as parasitizing the males of the paternal species for their sperm while discarding everything they actually contribute. The males do not appear to have been consulted.

From there, the ancestral hybrid lineage diversified further: hybridogenesis gave rise to full parthenogenesis, and then, twice independently, to triploid lineages carrying three distinct genomes.

The team recreated this trajectory in laboratory crosses, where each step demonstrably prepared the conditions for the next. Given that Bacillus stick insects have a one-year generation time, those lab crosses took years to complete.

The findings suggest that losing sex isn't necessarily an evolutionary dead end; a single genomic disruption can act as a catalyst for diversification rather than a ceiling.

The insects have been running this male-free experiment for 8,000 years. The results are in.

Read the full story at Phys.org, June 1, 2026

Hot Take:The conventional wisdom says ditching sex is a dead end. These stick insects have been making the conventional wisdom look slow since before agriculture existed.