I wonder if Ferengi evolved from some sort of hairless mammalian primate or possibly some form of amphibian. I'm thinking some form of mammal-like amphibian given Ferenginar's exceedingly rainy climate. I'd say more mammalian given their humanoid appearance, but perhaps with some characteristics of amphibians as well.
Maybe not completely hairless. Didn't Grand Nagus Zek have hair growing out of his lobes? Armin Shimerman complained that the first Ferengi to appear were directed to jump around like angry gerbils. The amphibian idea may have some merit, as Kira at least once called Quark a toad.
True, perhaps its a trait of Ferengi as they age that. However I'm thinking something like an amphibian or a mammal that has some form of amphibian characteristics are more or less Ferengi. Maybe the earliest ancestor of the Ferengi is some form of lung-fish or salamander-like creature.
Behaviorally the Ferengi always reminded me of ferrets or cats. Even their diet suggests this. We know the Ferengi do eat small prey--grubs, worms, snails, and so on, but I don't usually hear about their eating larger animals. My theory is that, similar to cats or ferrets, the Ferengi evolved from predators, but NOT apex predators the way humans and presumably Vulcans, Klingons, and Cardassians did (judging from behavior). Their fight-or-flight behavior, their threat displays and distress cries, and so on, and terror of confronting larger opponents while being willing to prey on smaller ones, AND even their contention that they have never engaged in the type of large-scale warfare seen by "apex" species like the ones I mentioned before, all fit with the idea of a non-apex-predator species. And the judgments passed on them by the "apex" species definitely seem like they would stem from such a fundamental disconnect in mindsets. I suspect that something really huge and nasty used to prey on them in their native swamps, but that something either went extinct at a fortuitous point in Ferengi evolution, or instead the Ferengi only began to hold them at bay after learning to control fire, make spear points, and other Stone Age technology. And maybe only truly eliminated this other species as a threat as their technology progressed further into Bronze Age/Iron Age equivalents.
Humans didn't evolve from apex predators though. Surely we only became apex after reaching the 'modern human' stage? All of which are very human qualities too.
I would think our ancestors were apex predators before hitting the homo sapiens sapiens stage, though. Whereas I don't imagine the Ferengi making that evolutionary leap. Perhaps their biology has yet to adapt to the new facts of life on their world.