The social brain hypothesis and crows

The social brain hypothesis posits that one of the reasons large brains developed is to allow us to live well in large social groups. With a large brain we could remember more people, allowing us to live in larger groups. These allowed us to search a larger area for food/defend a larger territory/provided more mating opportunities etc.; resulting in selection for a large brain. The feedback loop between the brain size and group size ensued, resulting in our large brains.

Whilst the social brain hypothesis has been thoroughly studied in primates, there are also many lesser known non-primate examples. Perhaps the most surprising of these is the Corvids (crows, jays, ravens and jackdaws). Whilst most people know that crows are very smart animals, few are aware of just how clever they are. In fact, they’re considered the most intelligence bird group (aside from some parrots) with a brain as big as a chimps’ (once body size is taken into account, obviously it isn’t literally as big as a chimps’).

The relationship between brain size and group size in primates

The most obvious example of Corvid intelligence is their use of tools. Crows make hooks from twigs, which they then use to “fish” for insects. They also alter the tips of other sticks to create barbed spears, which they stab into piles of leaves to skewere unsuspecting insects (I guess crows must really hate insects). But their tool-based intelligence does not end there.

Crow tool use

When presented with unfamiliar material, such as wire, they are able to work out that these can also be turned into tools (and so do that). This suggests that they understand why the tools are effective (because of their shape) and are not just blindly repeating innate or learned actions. They can also use tools to solve new problems on the first try, without any trial and error, suggesting they can think into the future and imagine the solution to these challenges.

Another fairly well known example of Corvid intelligence is their ability to mentally time travel. Many species of crow store food for later, but will dig up their caches not in the order they were buried but in the order they will decay (i.e. insects before nuts). In one test they were given two new kinds of food, which they buried and then retrieved randomly. However, when they were taught that one kind of food decayed quicker they adapted their behaviour and started retrieving that kind first, again demonstrating how flexible and innovative their behaviour can be (alas the research I’ve read does not explain how they were taught this, but I like to think it was done in a little crow-classroom with a crow-teacher writing on a crow-chalkboard).

Finally, we have their Machiavellian intelligence. Not many people know about this, but it is fascinating nonetheless. As I just said, crows like to bury food for later. However, this means that another crow can watch others, learn where they bury their food, then steal it later on. Other crows have realised this, so if they bury food whilst being watched by another crow they will soon return, dig up the food, then bury it another location where nobody else can see them! Again, this is a flexible, learnt behaviour. Only crows which have stolen someone else’s food (or seen theirs get stolen) will move it around.

look at him, you can just tell he’s plotting world domination

As that last example illustrates, most Corvids do have very complex interactions with others in their group so they may be under the influence of the social brain hypothesis. Larger brains allow them to live in larger groups (which is beneficail) and to do so without having their food stolen by others. So it may well be that the same forces which are driving our evolution are also influencing how the crows evolve. Rise of the Planet of the Corvids anyone?

Regardless of whether Hitchcock’s The Birds soon becomes factually accurate, I find these examples of “human” evolution in other animals fascinating, and I hope you also find some comfort in that fact as your doom circles over head, cawing.

Emery, N. J., & Clayton, N. S. (2004). The mentality of crows: convergent evolution of intelligence in corvids and apes. science, 306(5703), 1903-1907.

15 thoughts on “The social brain hypothesis and crows

  1. Pingback: The social brain hypothesis and crows « EvoAnth « Colin's mind

  2. What do you think of the idea that our intelligence is more for winning arguments with people than finding the truth? Basically, that we have evolved to battle more with our minds than our fists.

      • Look at the way people argue and debate. It seems they’re more interested in winning than arriving at the truth and will often lie and distort facts to do so.

        • Such debates are a relatively recent development in our history and would likely not have been a major factor influencing our evolution 1 or 2 million years ago, when our brain was enlarging.

          • Yeah, this wouldn’t be what started the evolution of our intelligence but it may be one selection pressure that emerged once we got pretty smart -once we developed big brains, we began using them to fight.

  3. Crows used to kind of creep me out due to their intelligence, but over time I’ve come to be fascinated by them. One minor negative: in urban environments, they seem to be driving out other species.

      • Quite honestly, there are some days when I’d hold the door open for them. They almost certainly couldn’t do a worse job.

        I’ve always loved the WG Sebald line, “Men and animals regard each other across a gulf of mutual incomprehension.” That gulf is incomprehensible enough with something close incredibly close (emotionally bonded) to humans as dogs.

        With crows…. the gulf must truly be incomprehensible. I always wonder what they’re “thinking” as they sit there, lined up on a roof peak, glaring down at me. I suspect they are wishing I was much, much lighter.

        • The fascinating thing is that they’re not mammals. Mammals share a fairly similar brain structure, so even though we can’t really understand them there is at least a bit of common ground. Birds have a different brain structure, so are yet another step removed from us. People talk about the difficulty we’d have holding conversation with a lion when a crow would be much more alien.

          • Fascinating and part of what makes them a little creepy/scary. It’s like intelligent lizards (which I consider birds pretty close to).

            Last week I happened to watch the PBS NOVA episode (from a couple years back) about crows. One experiment, tried for the first time, to require three distinct stages of tool use. First the crow had to haul up a short stick dangling from a string. Then it had to use the short stick to fish a longer stick out of a small cage. Then it could use the longer stick to retrieve a small piece of meat from another container.

            It did it with dispatch. Eerie as heck to watch, though.

          • I think that’s the case with any instance of advanced animal tool use. When I first saw capuchin monkeys using rocks to crack nuts it blew my mind (and freaked me out a little bit). After all, they’re monkeys! They’re not meant to be as intelligent as apes, yet here they are doing something only before documented in chimps and humans.

  4. Pingback: Bird brains? Crows remember your face | Tim Batchelder.com

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