What were the differences between the chimps that got the drugs and those that didn’t?
There were some differences in…behaviors like regurgitation and re-ingestion, and to a lesser degree, body rocking and other stereotypic movements. It seemed to improve social play in these animals, which is very nice to observe.
In the comparison group, abnormal behaviors even increased over time. So it’s very likely that the combination of behavioral treatment and medication had a good effect. But because it was started almost simultaneously, it’s really difficult to disentangle the effect of the diet change, the environmental enrichment, and the medication.
That’s interesting, because if you were going to do a proper study on this, you would try to isolate different treatments.
That’s right, you would control that. But if you have a human patient, you don’t start psychotherapy first, and then if it doesn’t work, pull in medication later, so it’s more a very practical approach.
Is this a treatment you would suggest for all those hundreds of other former laboratory chimps dealing with similar issues?
No. Some individuals with similar histories or a similar background are more resilient and do not develop abnormalities to such an extent. So I think you always have to take into account individual differences in vulnerability. With regard to the five hundred or so chimpanzees in captivity worldwide, the decision whether to give them medication has to be made individually.
You mentioned in your 2006 paper that apes might help us understand human mental illness. Can you talk a little bit about what apes have contributed to your field?
Difficult, difficult question. It seems to corroborate findings [in humans] suggesting that the combination of early traumatization and adverse experiences throughout the life span produce psychopathological syndromes.
Also, I find it interesting to see that relatively simple interventions like dietary change and environmental enrichment plus medication produce such profound improvements. My guess is this wouldn’t be the case in a human who grew up under similar circumstances. So the amazing conclusion could be that we as humans are still more vulnerable to adversity than even chimps are.
Why might that be?
It could be that when the human lineage split from the chimpanzee lineage, there were some genes selected in ourselves that make us more flexible behaviorally. We can certainly adapt to a greater range of environmental circumstances than chimpanzees can. That’s why we populated the globe and not chimps. But on the other hand, this could perhaps come at a cost. And the cost is perhaps increased susceptibility for psychological disturbances.
What do you think is going to happen to all the currently captive chimps?
Hopefully they will be retired to good sanctuaries, and in case they have pervasive behavioral problems, they should receive proper treatment. But because they can become 50 or perhaps even 60 years old, I think the problem will be around for at least another couple of decades.
What’s the next step for this project in the Netherlands?
The next step is to put others on medication—those that were in the comparison group—and see if it works as well as in the first intervention group. Maybe it’s a model for other sanctuaries, but this is something I don’t know.
Do you hope to influence the way that chimps are cared for in general?
I’m skeptical. It’s my hope, of course, but in light of the reservation people have about medication in general, and perhaps more specifically treatment of nonhuman primates, I have my doubts that it has much influence. But who knows?