Comic Strips

I can’t think of any species where this is true

Humans, as we're the ones with advanced social organizational structures.

But you could go more broadly if you liked. From apes to ants, complex stigmas are an expensive and dubiously beneficial social construct. Keeping things simple is less expensive and more efficient for any large organization.

Can you explain why you think the default state of nature is equality though?

The short of it is that it takes more effort to discriminate from a bureaucratic perspective. Any system that is gender or color blind necessarily has fewer rules, exceptions, and contradictions. If you have a toll booth on a road and you collect a fee for passage, a flat fee is easier to implement than a complex gradient based on nebulously defined characteristics.

In a pure state of (human) nature, absent the economic surpluses of an industrial state, discriminatory practices are limited by their material costs. You only get to Victorian Era states of hierarchy and social sorting when you enjoy the kind of social surplus that can afford a professional class dedicated to policing and punishing people who are out of line. And - even then - this kind of discrimination is primarily enforced at the highest social scales. The neglected underclass and the rural counties aren't dedicated resources to preempt miscegenation, to segregate the genders, or to enforce exotic codes of conduct common among the urban aristocracy.