Scientists working out of Simon Fraser University in British Columbia, Canada, have discovered an evolutionary oddity: a thriving genus of stick insects that have somehow survived 1.5 million years without having sex, reports

The stick bugs, which include several species from the genus Timema that are native to the western United States, are believed to have experienced the longest asexual period for an insect. The discovery could rewrite our understanding of the evolution of sexual reproduction.

The researchers were able to determine the last point in time the insect lines engaged in sex by utilizing a series of genetic analyses. They found that five Timema species (T. douglasi, T. monikensis, T. shepardi, T. tahoe and T. genevievae) have reproduced using only asexual reproduction for more than 500,000 years, while T. tahoe and T. genevievae were the record-breakers: they each reproduced asexually for well more than 1 million years.

How the stick insects have managed to avoid extinction after such a long period of celibacy is still largely a mystery. Although asexual reproduction can be highly efficient, sexual reproduction is typically a better evolutionary strategy in the long term because it adapts a population much quicker to environmental changes.

"Many genetic and ecological mechanisms have been suggested that could result in disadvantages of clonal reproduction. One common expectation of these mechanisms is that reproductive advantages gained by new clonal lineages will be quickly eroded over time," explained Tanja Schwander, co-author of the study.

The fact that asexuality in these stick insects has persisted over such a long period of time is therefore evidence that asexuality may not always result in the rapid extinction of a lineage. In other words, scientists may have overestimated the real value of sex.

At the very least, the findings complicate our traditional theories about the evolution of various reproductive forms.