A Savannah chimp eating a bush baby she caught with a spear
Chimps are the only species of great ape (except for us) that hunts and kills mammals. Sometimes even with spears. However, this makes up a relatively small part of their diet (some estimates put it at only 3%), so it is widely believed that the primary reason they hunt isn’t for food. The groups which hunt together are typically all males, so it has long been thought that it might actually be a social activity with all the men of the troupe bonding over the murder of another animal. But soon to be published research argues that we’ve underestimated the dietary importance of meat in the chimp diet.
The paper in question – creatively titled “Why do chimpanzees hunt?” – notes that although meat makes up a small amount of the food eaten overall, in the day to day life of a chimp its actually a significant lump. Obtaining the same number of calories through eating insects or fruit can take hours longer, so meat is really efficient. Plus it contains a bunch of nutrients not found in the plants which make up a large part of their diet, and is available year round (unlike the insects they often use to supplement their diet). In short, a lot of meat can be obtained really quickly whenever it is needed. It’s a really good back-up option.
But if meat is important for the diet, why do the males hunt in groups? Surely this decreases the amount of meat each individual gets. The female chimps who hunt with spears do it by themselves, perhaps the men simply have to catch up to the huge intellectual advance that is “being alone.” However, the authors have another idea: meat scraps.
A chimp hunting by themselves has a relatively low rate of success. Even when looking at the spear wielding ladies they were only seen successfully killing their prey a couple of times. Working as a group increases your chance of success, so in the long run it pays off. You might get less from each individual kill, but there are more successful hunts overall so it balances out. It would be interesting if someone who knew how computer models work would simulate this strategy to see if it is actually viable. Artem I’m looking at you.
This has some fairly interesting implications for human evolution, which is really the only reason anyone bothers looking at chimps in the first place. Screw understanding the world, how does it impact meeeeee! Our ancestors appear to have been hunting from 2.5 million years ago, and doing so on a much larger scale than chimps by 1.8 million years ago. If this meat scraps idea has any merit (Artem, still looking at you), then this would suggest our ancestors would have to be working in groups. Groups probably larger (given what they’re hunting) and more common (given the amount they’re hunting) than what chimp are doing.
Around this time our brains also began to get bigger. A popular explanation for this is that it is connected to our social lives, with bigger groups putting a strain on our memory (having to remember who is who and how they’re connected and do we like them) so driving us to evolve bigger and better brains. Could it be that the main driver from these large groups in the first place was hunting? Hunting forced us to live in big groups which made our brains get bigger which made us be awesome?
If so lets hope the chimps don’t start eating more than 3% meat. They’re strong, innovative creatures and if their brain begins to get bigger, Dawn of the Planet of the Apes (a film I’m really looking forward to) might become more accurate than we’d like.
Reference
Tennie, C., O’Malley, R. C., & Gilby, I. C. (2014). Why do chimpanzees hunt? Considering the benefits and costs of acquiring and consuming vertebrate versus invertebrate prey. Journal of Human Evolution