Which sounds less improbable to you?
1. The cosmos came into existence by a process we don’t entirely understand just yet, but we think that in the first few moments of its emergence most of the laws of physics and matter we consider de rigeur now were somehow coalesced into a reasonably predictable set of steady states. Following those simple rules all the heavier elements past hydrogen fused in the hearts of ancient stars, and some of those elements coalesced into compounds which developed a means to remain internally coherent and, eventually, a way to replicate their patterns with a reasonable degree of verisimilitude. However, the processes involved in that replication were so complex that occasional errors crept in, some of which caused replication failure but most of which had no apparent effect — until the setting changed somehow, forcing certain erroneous patterns into a state of greater success at replication. After several million years of such errors and successes, eventually some of the universe’s elements developed an emergent property called consciousness, contingent entirely upon a niche position in an otherwise entirely-reactive and nonstochastic field. Of course, this current understanding could well change with further iterations of discovery and refinement; science is a lot like a calculus approach to a limit, always working toward complete understanding but always bafflingly, tantalizingly just falling short — which is frustrating to many, but beautiful to some.
— or —
2. God did it. Now eat the cracker, drink the wine and stop asking so many questions