Here at the Grail we have previously written about the idea that microscopic parasites might manipulate the behaviour of their macroscopic hosts, as well as posting videos such as this fascinating TED talk on the topic. In particular, the brain parasite toxoplasma gondii, which has been shown to actually ‘rewire’ the fear-related sections of the brains of its rodent hosts, changing their behaviour in order to make it more likely they will be eaten by felines. The reason? Toxo needs the gut of a cat to reproduce.
There is some evidence that Toxo also changes the brains of other species it inhabits, including humans, but this has largely been thought to be an indirect effect of a behaviour that is aimed specifically at affecting only rodents. But a new experiment run with chimpanzees may make us reconsider that assumption:
Clémence Poirotte, an evolutionary biologist at the Center for Functional and Evolutionary Ecology in Montpellier, France, wondered if our understanding of Toxoplasma might be limited by the paltry number of species in which its manipulations had been studied. She and her colleagues decided to focus on chimpanzees, running an experiment on 33 apes at a primate research center in Gabon, nine of which had Toxoplasma infections.
Instead of testing the reactions of chimpanzees to the odor of house cats, Ms. Poirotte and her colleagues turned to leopards, their natural predators. A veterinarian at a Gabon zoo supplied them with leopard urine, and they poured drops of it on the fence enclosing the space in which the chimpanzees lived.
Stepping back from the fence, the scientists observed the apes to see how they responded. They also ran the same experiment with urine from three species that are not chimpanzees’ natural predators: humans, lions and tigers.
The researchers found that the Toxo-infected chimpanzees were not as alarmed by the scent of the leopard urine as the non-infected chimps, suggesting they may have developed the same recklessness observed in Toxo-infected rodents. Being primates, like us, this could mean that Toxo also affects our behaviour.
While there is much more research required before it is confirmed, “it certainly suggests that Toxo’s behavioral effects in humans may be less of an irrelevant dead end than was always assumed,” said biologist Dr. Robert Sapolsky said.