From 1971 to 1985, primatologists Biruté Galdikas and Rod Brindamour released more than 90 rehabilitated orangutans into the wilds of Borneo. Most of the great apes—which live in just two places, Borneo and Sumatra—had been confiscated from the illegal pet trade. At the time, orangutans were considered a single species. But today, via advances in genetics and morphological studies, they are considered two separate species, with at least three reproductively distinct subspecies. Now, new research has shown that those early rewildings have transformed local populations—for better and for worse. To find out whether the wrong types of orangutans had been accidentally released scientists analyzed 44 years of data from an orangutan rehabilitation site at Borneo’s Camp Leakey. Using fecal samples, they also studied the genetics of the camp’s current ape population. They found that two reintroduced females were not from the local subspecies, and had since given birth to at least 22 hybrid offspring (shown above). Rani, one of the two, has a large family with at least 14 descendants. The researchers say they may be the lucky beneficiaries of something called “hybrid vigor,” which occasionally takes hold when two distinct populations breed. But Siswoyo has had few offspring, many of whom suffer from various health issues. Those ailments could be caused by “outbreeding depression,” the result of mixing genetically distinct populations. The scientists estimate that nine males from these mixed-species unions have carried their “cocktail” of genes into the wilds of Tanjung Puting National Park—with unknown repercussions. This may be but the tip of the iceberg, given the number of reintroduced orangutans, the researchers write in today’s Scientific Reports. And they warn that other wildlife sanctuaries may be inadvertently doing the same thing—and ultimately harming the health and genetic viability of threatened wild populations.