Why have humans evolved conciousness?

I don't think you can ever ask or answer for that matter WHY questions in biology. The only answer there is: because it works. Asking why questions implies that there was a reason, and reason cannot exist alone by itself. Reason is held by someone or something. And reason is something that doesn't exist, it is something we created and use for our own purposes and we cannot attribute it to anything else having one. Now, if you asked "how?", that's an answer biology was created for.

There could have been many outcomes to everything in biology but this is the one that appeared and works. This doesn't mean that it is some sort of theoretical or practically optimum, but the law of this universe is survive long enough to improve if needed.

I know that this is an opinion, but it's as close to the answer that you can get. If someone gives an answer to the WHY question, you could never prove it, or you could find evidence for all the possible reasons. And we can't also tap into the reasons of the universe because our intellect and modes of expression are way lower than the universe has.

Animals are not self aware, sentience is the quality of placing yourself in time and space, and the capability of introspection. We humans know we exist, we know we live in a universe, we ponder what's the meaning of life, where we came from and how we came to exist, where we go after we die, animals don't, they act by instinct and have different levels of intelligence, their behavior is written in their DNA code, but they aren't self-aware, this is the basic trait that separates us from animals.

Concerning how we became self-aware, that will depend on your beliefs (another trait of our advanced intelligence), but those who believe in evolution pretty much agree that we developed sentience because our brains developed much further than that of any other species, our advanced cortex and cognitive system gave us this ability. Different religions also have different accounts to our origin and history, in the proto-Indo-European cosmology for example, we are descendant of aliens, called pleiadians or nordic aliens, they came to earth through a portal in the sun, and brought their seed to our planet and gave origin to us, all our knowledge and manifestation of our humanity, like science, art... come from them.

Why did humans/animals evolve to become self-aware of their own thoughts.

Answer is pretty simple. Most mammals are self aware... it is just a matter of degree. It is a lot more advance in humans, but it is there in animals. like pride of Lioness hunting... setting up an ambush together... which means a lion can predict what zebra will do in a situation. And what other lioness will do.

And why have it? The answer is simple... being aware of you own thought, is basically being able to prediction the thoughts of others. And this is pretty useful.

We have the example of lioness pride ambush hunting. It requires a degree of self awareness in order to communicate and in heat of the chase predict what the other members of your pride will do and what will the prey animal will do.

Being alpha (wolf, lion, chimp, elephant, hyena, meerkats) is great. There are many biological benefit (first to eat, drink and have babies). However for a there to be an alpha, there must first be a group to be alpha over. And when there is a group, there is a beta, and while beta might not be able to beat you individually, beta might team up with delta..to remove you.

So as you can see, living in groups quickly leads to complications. And if you can understand others, you can use others to benefit yourself. Much selection pressure there for to evolve consciousness.

This is really a philosophy question because for now, we have no clue how consciousness works. But other answers have correctly noted that we know it's closely related to our ability to learn, reason and remember.

There are some attempts to explain it though - you could now the famous TED talk about the illusion of consciousness by the philosopher Daniel Dennet. By evolutionary means, we can mainly study the concept of self.

One of the simple philosophies trying to explain consciousness is panpsychism. Panpsychism is virtually a part of hinduism and buddhism and says that everything has some degree of consciousness and our mind is one of the emergences of unity of many little conscious things.

Probably density of cortical columns. I tested this on a mouse recently, it was aware I was trying to help it and actually walked calmly into the jar. Released it but did wonder if it will make an appearance again one day.

Perhaps in this case, neural nets are not complicated enough unless the connectivity threshold is in a critical range. This is apparently why we are one of only three intelligent species on this planet, sharing this with dolphins and African Grey parrots. Four if you count octopi.

I speculated a while back based on my knowledge that connectivity modulators like psilocin, xenon and other compounds could be used to trace the actual neural connections responsible. This has been linked to Orch-OR and other QC like phenomena, also allowing for strong AI to be developed by synchronizing classical processors with a quantum link using entangled photons.

Natural selection doesn't select for the type of consciousness. It selects for brains that work for its purposes. The brain I think is like a Conway's game of life. It theoretically can pull off all kinds of tasks, and that can be explained just by the laws of physics acting on the brain.

The question of how the brain creates consciousness is an entirely different question maybe a philosophical one. I have aspergers. I sometimes do some abstract thinking. I sometimes sort of feeling like I'm conceiving of an object with properties that most intuitive theories prove cannot exist. They would say it's just my brain inventing the sentence "This object has those properties" and they're probably right. However, I sometimes actually have a small bit of feel for thinking in one and would feel like I'm conceiving of a real object which is distinct from its formalization which people would see if they looked at an image of my brain. I think we then decide to define consciousness according to the way the brain is in that kind of way.