(Image: Philip Harris)
AS PhD research projects go, Brian Wisenden’s was enviable: wading knee-deep in shallow streams in the Costa Rican tropical dry forest, watching baby fish darting through the crystal clear waters. By recording their growth and numbers, he hoped to get an insight into their risks of being eaten.
Instead, he witnessed something odd. Many broods were increasing in numbers, not decreasing, as they were picked off by predators. In these groups, some of the fry were smaller than others, suggesting they weren’t siblings. Wisenden had accidentally discovered that the fish, called convict cichlids, adopt each other’s offspring. Why would they do that, he wondered?
In the human realm, we think of adoption as a good and selfless act. But in nature, its presence is puzzling. Taking on the burden of rearing offspring to which they have no genetic link would seem to reduce an animal’s chances of survival or at least provide no gain, meaning it couldn’t have evolved via natural selection. Yet adoption is surprisingly common in the wild. As Wisenden and others start to understand why, they are finding that animals adopt for all sorts of reasons. In some cases, the practice is far from benign, with disturbingly dark underpinnings. But in others it can have remarkable benefits, not just for adoptees but also for foster parents and even their natural offspring.
“Adoption can have disturbingly dark underpinnings”
Nuclear families are a rarity in nature: many parents simply abandon their offspring to their fate. Where parenting does occur, it takes myriad forms. In some cases childcare falls on individuals who aren’t the parents