00:00We followed chimpanzees around the forest, these are habituated chimpanzees, and collected
00:08fruits from underneath where they were foraging, as well as on the ground.
00:13And we assed them for their alcohol concentrations using a few different methods.
00:18And using that data, combined with long-term data from these decades-long field sites about
00:24chimpanzee feeding, we were able to determine that they consume 14 grams of ethanol per
00:31day on average.
00:33This is from across 21 species of fruits and hundreds of samples.
00:38And did you find that the chimps are actively seeking out the fruit that has the most alcohol
00:42content in it?
00:45This was just an average take on what we were finding as they were consuming fruits.
00:51We weren't able to do a behavioral side to it.
00:55So it's potentially possible that they're targeting higher concentrations, fruits that we weren't
01:02able to find because they're more scarce.
01:06And alternatively, they could be avoiding alcohol by targeting fruits that have very little because
01:12we measured a full spectrum of values.
01:15So tell us about this drunken monkey hypothesis.
01:19The idea that the human appetite for alcohol was inherited from our primate ancestors.
01:24Have there been much evidence of this before your research?
01:28Yes.
01:29So we know that there's alcohol, low concentrations of it in fruits all over the world, but it
01:36was never so systematically studied in relation to one species of seed disperser of animal, in
01:43this case chimpanzees.
01:46So it definitely moves the field forward.
01:50The drunken monkey hypothesis sort of hinges on the idea that our remote ancestors millions
01:57of years ago were consuming fruits in their diet and they were encountering these low level
02:02concentrations of ethanol in a similar way that chimpanzees do today.
02:07And now we found that indeed that is the case.
02:09So you say low level concentrations, but when the chimps consume the fermented fruit, are
02:15they becoming drunk?
02:18So this is the equivalent of say drinking a lager over the course of breakfast, lunch and dinner.
02:25And you're sort of stretching it out over a long period of time.
02:28We tend to think of alcohol in terms of liquid, high concentration kind of doses where you're
02:36able to drink it very quickly.
02:38And in this case, it's more comparable for what the chimpanzees are doing to compare it
02:43to eating very fermented food, say a whole lot of it, but throughout the day.
02:49So you're unlikely to catch much of a buzz in that sense.
02:53But, you know, these are average concentrations.
02:56And when some species of fruit are in season, the chimpanzees kind of binge feed, they really
03:02tank up.
03:03And when that happens, then it very well may get more highly available, the ethanol.
03:11And Alexia, is there a social aspect to foraging for fermented fruit as a troop or as a whoop?
03:18I'm not quite sure what the collective noun is for chimpanzees.
03:21Yes, so they live in different communities.
03:27And actually, in the paper, we talk about this, that they tend to go on patrols and against
03:33or to patrol for neighboring communities.
03:36And these encounters can get deadly.
03:38So scientists try to predict what factors caused them or made them predisposed to going in these
03:45controls.
03:46And they found that it's when there's a large group of chimp, male chimpanzees that are already
03:49together.
03:51And then they found that it's when they're in this fig tree called ficus macuso, they really
03:55love these figs.
03:57And the first part makes sense when there's a lot of male chimps together, they'll go patrolling
04:00the forest.
04:01But why these fruits?
04:03And partly these trees are really big, so a lot of chimps can congregate all at once.
04:08And they tank up.
04:09You know, anecdotally, they eat a lot of fruits so that they get a good caloric ballast and
04:15they have enough sugar in their stomachs to deal with whatever's coming.
04:20And it's tantalizing to think that maybe there's, you know, some effect of some encouragement
04:25from the ethanol component.
