'People respond to incentives.' So says the cornerstone of economics. But there's nothing unusual about people in this regard.
I realized this when I finally got Lucius to use his catflap by applying basic economics. First, I reduced the cost of using it by wedging it open. Then, I raised the opportunity cost of his preferred alternative to using the catflap - meowing at me to open a door - by going out for several hours on a visit to Cromford. And - most importantly I suspect - I gave him a high-powered incentive to use the flap, in the form of a bowl of tuna on the other side of it.
And this worked. I returned from Cromford to an empty bowl.
Lucius, then, responds to incentives.
In truth, though, such responses are common in the animal kingdom. This paper shows that

Standard price theory does a remarkably good job of describing capuchin purchasing behavior; capuchin monkeys react rationally to both price and wealth shocks.

Another demonstrates (pdf) that the income-leisure trade-offs of pigeons are in many respects similar to those of humans. There's evidence (pdf) that squirrels respond to the risk of theft of food by hiding their food stores better. And Leonard Green and colleagues have found that rats and pigeons discount (pdf) the future in a similar way to humans.
In terms of responses to incentives, there is, therefore, nothing unique about humans. From an economist's point of view, Gulshan Khan seems correct to say that 'there is no separate object, entity, or being called 'man''.
This raises some tricky philosophical issues, such as:
1. Response to incentives is no evidence of high intelligence. It can be seen not just in primates and cats but in supposedly 'lower' animals too.
2. What's the link between response to incentives and conscious agency? If the two are linked, then the fact that animals respond to incentives is evidence that they are conscious beings like us - in which case the argument for animal rights is surely strengthened.
However, the two might not be linked. Sunflowers turn themselves towards the sun, apparently responding to incentives, but no-one attributes consciousness to them. If we take this line, though, human economic behaviour is no evidence that humans have free will.
3. Given that economic behaviour is common in the animal kingdom, what - if anything - makes humans unique? It's too glib to say that humans have a sense of morality that sometimes can over-ride incentives - as, for example, when people choose to behave well even when incentives dictate otherwise. If we define morality as other-regarding behaviour, we would have to say that social creatures such as ants and bees display more of it than humans.
Instead, here's a possibility. What makes humans unique is that we are an admixture. We are neither wholly pro-social like ants or bees, nor wholly selfishly amoral. And we are neither herd animals nor solitary ones such as cats. In other words, the distinctiveness of humans lies in the fact that our behaviour is to some (large?) degree unpredictable.