How did gravity evolve?

Gravity was the first force to split from the other three fundamental universal forces (these being the electromagnetic, strong nuclear and weak nuclear forces) during the early expansion of the universe - around the end of the Planck epoch - through phase transitions of symmetry breaking. This basically defined the gravitational relationship among the others as we know it today, and hence gravity as a unique force has existed for the entirety of the known universe.

However, beyond that, gravity is at best hazy and at worst unexplainable because of those same definitions and properties. Active research includes gravity and how it works as a major focus, with efforts so far unable to unify it with the other three forces.