The world is full of causes and effects. The wind blows and the trees sway. The wind blowing causes the tree to sway. The wind is the causative agent. Now biologically there is a strong adaptive reason for being able to recognize causative agents. If you're a monkey and a tree branch moves it is useful to be able to tell if the branch moved due to wind or if the branch moved due to a snake or other predator.
Humans are really good at finding causative agents. We'll even make them up. Most myths deal with trying to provide causative agents for effects where we couldn't see what caused the effect. Where did the wind come from? Wind is an effect, effects have causes, and causes have agents. In ancient times, humans didn't understand high pressure systems and would make up myths about what caused the wind. And so we end up with Aeolus the ruler of the winds in Greek mythology (as one example).
This is an example of what some scientists would call a hidden causative agent. And humans are the only creatures known to employ them. Maybe. I recently read about a paper where some scientists were studying whether a species of crow had a concept of a hidden causative agent.
The scientists had a structure where the crows were able to sit and observe a stick. When a person went behind a curtain the stick would move around and prevent the crow from accessing some food. The crows understood this reasonably well. There was a cause and effect, with the human as the expected causative agent. So far so good.
The scientists actually hadn't had the human behind the curtain cause the stick to move, that was actually done by someone else the crow never saw. So next the scientists had the human not go behind the curtain, and then the stick moved. Thus the causative agent became hidden. This meant that the crow had to try to figure out what caused the stick to move.
So the crows were observed to see how they responded. If they believed there was a hidden agent, then they would remain wary about the stick moving even when there was no human behind the curtain. And this is what they observed.
Actually what they observed was that if the crow saw that the human had left from behind the curtain, they wouldn't inspect the stick too much. If they didn't see a human depart from behind the curtain then they would do much more inspection of the stick before they'd return to doing what they'd been doing before. In other words when they couldn't see a human leave from behind the curtain, they'd try to look behind the curtain.
Is this another sign of intelligence of crows? Perhaps. That seems to be one of the results that these scientists take from the experiment. If it is a sign, it's one that most of us should work to apply in our own lives. When you don't know the cause, well, try to look behind the curtain. After all, Toto did.
(To read more about this check out this blog post. )