In the cartoon Dilbert doesn't really provide rational evidence for his claim either.

That doesn't mean he doesn't have any.

In this case there clear rational evidence that evolution evolved human's to try to show their high status by debating. There's little rational evidence that evolution gave people the goal of finding truth.

If the only point of debating was status, people would evolve not to listen to what anyone else says. Furthermore, the results of debates and human reasoning (flawed as it is) is correlated with truth; if this wasn't the case, we'd still be on the savannah getting chased by lions.