The notion of an "evolving brain" appears to make sense. However, it only makes sense if one assumes that physical time passes.
The fact of the matter is that physical time does not pass. Instead, all spacetime events coexist in parallel with one another: The physical present coexists with the physical past and future.
Let us consider two events: A and B. If event B happens after event A, one can suggest that event B evolved from event A. However, if event B coexists with event A, one cannot regard B as having "evolved" from A.
The 21st century AD human brain coexists with the brains of species that exist in the year 100 million BC. The modern human brain cannot be said to have "evolved" from the brains of animals that exist in the year 100 million BC. In fact, the human brain cannot be said to have evolved from the brain of any organism that exists at any point in history.
A given species does not come into existence by "evolving" from another species. In the "block universe," all physical organisms (past, present, and future) coexist in parallel with one another.
It is true that eggs and chicken both exist today (the two coexist "now"). But that is not the point that I am making.
I am not talking about the coexistence of two present events (e.g., today's eggs and chicken). I am talking about the coexistence of the present with the past!
The commonsense view of physical time is that past and present do not coexist with one another. However, physicists tell us that this commonsense view is wrong. They tell us that past and present really do coexist.
Scientists have conducted experiments with moving atomic clocks. The results of these experiments force us to accept the view that past and present exist "in parallel" rather than "in succession."
You asked: "How did we get here?" This is a meaningful question in Newton's universe (i.e., in a universe in which time passes objectively). However, the question has no meaning in Einstein's universe. (In a four-dimensional world, the present does not "come from the past." The present coexists in parallel with the past.)
Does this mean that in Einstein's universe nothing ever happens? Nothing ever changes? I just cannot get my head around: 'the present coexists with the past'. Does it makes sense to talk about past, present and future when they are all now, in the present? Just trying to understand your ideas.
Many philosophers argue that physical time cannot pass.
Dates (e.g., Jan. 1, Jan. 2, etc.) are simply locations in time. Dates do not move through time. And as we know, time itself does not "move" or "go" anywhere.
It is conceivable that consciousness somehow flows relative to physical time. However, physical time itself cannot flow or pass.
I suggest a model for time flow in my paper "Temporal Passage." The paper can be accessed at the following site(s):
Target Article 61